Differential relational memory impairment in temporal lobe epilepsy

OBJECTIVE

Temporal lobe epilepsy (TLE) is typically associated with pathology of the hippocampus, a key structure involved in relational memory, including episodic, semantic, and spatial memory processes. While it is widely accepted that TLE-associated hippocampal alterations underlie memory deficits, it remains unclear whether impairments relate to a specific cognitive domain or multiple ones.

METHODS

We administered a recently validated task paradigm to evaluate episodic, semantic, and spatial memory in 24 pharmacoresistant TLE patients and 50 age- and sex-matched healthy controls. We carried out two-way analyses of variance to identify memory deficits in individuals with TLE relative to controls across different relational memory domains, and used partial least squares correlation to identify factors contributing to variations in relational memory performance across both cohorts.

RESULTS

Compared to controls, TLE patients showed marked impairments in episodic and spatial memory, with mixed findings in semantic memory. Even when additionally controlling for age, sex, and overall cognitive function, between-group differences persisted along episodic and spatial domains. Moreover, age, diagnostic group, and hippocampal volume were all associated with relational memory behavioral phenotypes.

SIGNIFICANCE

Our behavioral findings show graded deficits across relational memory domains in people with TLE, which provides further insights into the complex pattern of cognitive impairment in the condition.

Graded and sharp transitions in semantic function in left temporal lobe

Recent work has focussed on how patterns of functional change within the temporal lobe relate to whole-brain dimensions of intrinsic connectivity variation (Margulies et al., 2016). We examined two such 'connectivity gradients' reflecting the separation of (i) unimodal versus heteromodal and (ii) visual versus auditory-motor cortex, examining visually presented verbal associative and feature judgments, plus picture-based context and emotion generation. Functional responses along the first dimension sometimes showed graded change between modality-tuned and heteromodal cortex (in the verbal matching task), and other times showed sharp functional transitions, with deactivation at the extremes and activation in the middle of this gradient (internal generation). The second gradient revealed more visual than auditory-motor activation, regardless of content (associative, feature, context, emotion) or task process (matching/generation). We also uncovered subtle differences across each gradient for content type, which predominantly manifested as differences in relative magnitude of activation or deactivation.

Volumetric analysis of hippocampal subregions and subfields in left and right semantic dementia

Two variants of semantic dementia are recognized based on the laterality of temporal lobe involvement: a left-predominant variant associated with verbal knowledge impairment and a right-predominant variant associated with behavioural changes and non-verbal knowledge loss. This cross-sectional clinicoradiologic study aimed to assess whole hippocampal, subregion, and/or subfield volume loss in semantic dementia versus controls and across its variants. Thirty-five semantic dementia participants and 15 controls from the Neurodegenerative Research Group at Mayo Clinic who had completed 3.0-T volumetric magnetic resonance imaging and 18F-fluorodeoxyglucose-positron emission tomography were included. Classification as left-predominant (n = 25) or right-predominant (n = 10) variant was based on temporal lobe hypometabolism. Volumes of hippocampal subregions (head, body, and tail) and subfields (parasubiculum, presubiculum, subiculum, cornu ammonis 1, cornu ammonis 3, cornu ammonis 4, dentate gyrus, molecular layer, hippocampal-amygdaloid transition area, and fimbria) were obtained using FreeSurfer 7. Subfield volumes were measured separately from head and body subregions. We fit linear mixed-effects models using log-transformed whole hippocampal/subregion/subfield volumes as dependent variables; age, sex, total intracranial volume, hemisphere and a group-by-hemisphere interaction as fixed effects; and subregion/subfield nested within hemisphere as a random effect. Significant results (P < 0.05) are hereby reported. At the whole hippocampal level, the dominant (predominantly involved) hemisphere of both variants showed 23-27% smaller volumes than controls. The non-dominant (less involved) hemisphere of the right-predominant variant also showed volume loss versus controls and the left-predominant variant. At the subregional level, both variants showed 17-28% smaller dominant hemisphere head, body, and tail than controls, with the right-predominant variant also showing 8-12% smaller non-dominant hemisphere head than controls and left-predominant variant. At the subfield level, the left-predominant variant showed 12-36% smaller volumes across all dominant hemisphere subfields and 14-15% smaller non-dominant hemisphere parasubiculum, presubiculum (head and body), subiculum (head) and hippocampal-amygdaloid transition area than controls. The right-predominant variant showed 16-49% smaller volumes across all dominant hemisphere subfields and 14-22% smaller parasubiculum, presubiculum, subiculum, cornu ammonis 3, hippocampal-amygdaloid transition area (all from the head) and fimbria of non-dominant hemisphere versus controls. Comparison of dominant hemispheres showed 16-29% smaller volumes of the parasubiculum, presubiculum (head) and fimbria in the right-predominant than left-predominant variant; comparison of non-dominant hemispheres showed 12-15% smaller cornu ammonis 3, cornu ammonis 4, dentate gyrus, hippocampal-amygdaloid transition area (all from the head) and cornu ammonis 1, cornu ammonis 3 and cornu ammonis 4 (all from the body) in the right-predominant variant. All hippocampal subregion/subfield volumes are affected in semantic dementia, although some are more affected in both dominant and non-dominant hemispheres of the right-predominant than the left-predominant variant by the time of presentation. Involvement of hippocampal structures is apparently more subregion dependent than subfield dependent, indicating possible superiority of subregion volumes as disease biomarkers.

Age differences in the neural processing of semantics, within and beyond the core semantic network

Aging is associated with functional activation changes in domain-specific regions and large-scale brain networks. This preregistered Functional magnetic resonance imaging (fMRI) study investigated these effects within the domain of semantic cognition. Participants completed 1 nonsemantic and 2 semantic tasks. We found no age differences in semantic activation in core semantic regions. However, the right inferior frontal gyrus showed difficulty-related increases in both age groups. This suggests that age-related upregulation of this area may be a compensatory response to increased processing demands. At a network level, older people showed more engagement in the default mode network and less in the executive multiple-demand network, aligning with older people's greater knowledge reserves and executive declines. In contrast, activation was age-invariant in semantic control regions. Finally, older adults showed reduced demand-related modulation of multiple-demand network activation in the nonsemantic task but not the semantic tasks. These findings provide a new perspective on the neural basis of semantic cognition in aging, suggesting that preserved function in specialized semantic networks may help to maintain semantic cognition in later life.

Semantic knowledge of social interactions is mediated by the hedonic evaluation system in the brain

Attaching semantic meaning to sensory information received from both inside and outside our bodies is a fundamental function of the human brain. The theory of Controlled Semantic Cognition (CSC) proposes that the formation of semantic knowledge relies on connections between spatially distributed modality-specific spoke-nodes, and a modality-general hub in the anterior temporal lobes (ATLs). This theory can also be applied to social semantic knowledge, though certain domain-specific spoke-nodes may make a disproportionate contribution to the understanding of social concepts. The ATLs have strong connections with spoke-node structures such as the subgenual ACC (sgACC) and the orbitofrontal cortex (OFC) that play an important role in predicting the hedonic value of stimuli. We hypothesized that in addition to the ATL semantic hub, a social semantic task would also require input from hedonic evaluation structures. We used voxel based morphometry (VBM) to examine structural brain-behavior relationships in 152 patients with neurodegeneration (Alzheimer's disease [N = 12], corticobasal syndrome (N = 18], progressive supranuclear palsy [N = 13], behavioral variant frontotemporal dementia [N = 56], and primary progressive aphasia (PPA) [N = 53]) using the Social Interaction Vocabulary Task (SIVT). This task measures the ability to correctly match a social term (e.g. "gossiping") with a visual depiction of that social interaction. As predicted, VBM showed that worse SIVT scores corresponded with volume loss in bilateral ATL semantic hub regions, but also in the sgACC, OFC, caudate and putamen (pFWE <0.05). These results support the CSC model of a hub-and-spoke organization of social semantic knowledge with the ATL as a domain-general semantic hub, and ventromedial and striatal structures as domain specific spoke-nodes. Importantly, these results suggest that correct comprehension of social semantic concepts requires emotional 'tagging' of a concept by the evaluation system, and that the social deficits observed in some neurodegenerative disease syndromes may be caused by the break-down of this mechanism.

Common brain activation and connectivity patterns supporting the generation of creative uses and creative metaphors

Recent studies and reviews suggest that creative thinking is at least partly a domain-general cognitive ability, dependent on consistent patterns of brain activity including co-activation of the executive control and default mode networks. However, the degree to which the generation of ideas in different creative tasks relies on common brain activity remains unknown. In this fMRI study, participants were asked to generate creative ideas in both a uses generation task and a metaphor production task. Whole-brain analysis showed that generation of creative uses (relative to conventional uses) activated the bilateral inferior frontal gyrus (IFG), medial prefrontal cortex, left supplementary motor area, left angular gyrus (AG), left thalamus, and bilateral cerebellum posterior lobe. The generation of creative metaphors (relative to conventional metaphors) activated dorsal medial prefrontal cortex (dmPFC) and left AG. Importantly, regions active in both creative use and creative metaphor generation included the dmPFC and left AG. Psycho-physiological interactions analysis showed that the left AG was positively connected to the right precentral gyrus, and the dmPFC to the left IFG in both creative tasks. Our findings provide evidence that the generation of creative ideas relies on a core creative network related to remote semantic association-making and conceptual integration, offering new insight into the domain-general mechanisms underlying creative thinking.

Baseline Conceptual-Semantic Impairment Predicts Longitudinal Treatment Effects for Anomia in Primary Progressive Aphasia and Alzheimer's Disease

Background

An individual's diagnostic subtype may fail to predict the efficacy of a given type of treatment for anomia. Classification by conceptual-semantic impairment may be more informative.

Aims

This study examined the effects of conceptual-semantic impairment and diagnostic subtype on anomia treatment effects in primary progressive aphasia (PPA) and Alzheimer's disease (AD).

Methods & Procedures

At baseline, the picture and word versions of the Pyramids and Palm Trees and Kissing and Dancing tests were used to measure conceptual-semantic processing. Based on norming that was conducted with unimpaired older adults, participants were classified as being impaired on both the picture and word versions (i.e., modality-general conceptual-semantic impairment), the picture version (Objects or Actions) only (i.e., visual-conceptual impairment), the word version (Nouns or Verbs) only (i.e., lexical-semantic impairment), or neither the picture nor the word version (i.e., no impairment). Following baseline testing, a lexical treatment and a semantic treatment were administered to all participants. The treatment stimuli consisted of nouns and verbs that were consistently named correctly at baseline (Prophylaxis items) and/or nouns and verbs that were consistently named incorrectly at baseline (Remediation items). Naming accuracy was measured at baseline, and it was measured at three, seven, eleven, fourteen, eighteen, and twenty-one months.

Outcomes & Results

Compared to baseline naming performance, lexical and semantic treatments both improved naming accuracy for treated Remediation nouns and verbs. For Prophylaxis items, lexical treatment was effective for both nouns and verbs, and semantic treatment was effective for verbs, but the pattern of results was different for nouns -- the effect of semantic treatment was initially nonsignificant or marginally significant, but it was significant beginning at 11 Months, suggesting that the effects of prophylactic semantic treatment may become more apparent as the disorder progresses. Furthermore, the interaction between baseline Conceptual-Semantic Impairment and the Treatment Condition (Lexical vs. Semantic) was significant for verb Prophylaxis items at 3 and 18 Months, and it was significant for noun Prophylaxis items at 14 and 18 Months.

Conclusions

The pattern of results suggested that individuals who have modality-general conceptual-semantic impairment at baseline are more likely to benefit from lexical treatment, while individuals who have unimpaired conceptual-semantic processing at baseline are more likely to benefit from semantic treatment as the disorder progresses. In contrast to conceptual-semantic impairment, diagnostic subtype did not typically predict the treatment effects.

Critical role of the ventral temporal lobe in naming

OBJECTIVE

Lexical retrieval deficits are characteristic of a variety of different neurological disorders. However, the exact substrates responsible for this are not known. We studied a large cohort of patients undergoing surgery in the dominant temporal lobe for medically intractable epilepsy (n = 95) to localize brain regions that were associated with anomia.

METHODS

We performed a multivariate voxel-based lesion-symptom mapping analysis to correlate surgical lesions within the temporal lobe with changes in naming ability. Additionally, we used a surface-based mixed-effects multilevel analysis to estimate group-level broadband gamma activity during naming across a subset of patients with electrocorticographic recordings and integrated these results with lesion-deficit findings.

RESULTS

We observed that ventral temporal regions, centered around the middle fusiform gyrus, were significantly associated with a decline in naming. Furthermore, we found that the ventral aspect of temporal lobectomies was linearly correlated to a decline in naming, with a clinically significant decline occurring once the resection extended 6 cm from the anterior tip of the temporal lobe on the ventral surface. On electrocorticography, the majority of these cortical regions were functionally active following visual processing. These loci coincide with the sites of susceptibility artifacts during echoplanar imaging, which may explain why this region has been previously underappreciated as the locus responsible for postoperative naming deficits.

SIGNIFICANCE

Taken together, these data highlight the crucial contribution of the ventral temporal cortex in naming and its important role in the pathophysiology of anomia following temporal lobe resections. As such, surgical strategies should attempt to preserve this region to mitigate postoperative language deficits.

Temporopolar regions of the human brain

Following prolonged neglect during the formative decades of behavioural neurology, the temporopolar region has become a site of vibrant research on the neurobiology of cognition and conduct. This turnaround can be attributed to increasing recognition of neurodegenerative diseases that target temporopolar regions for peak destruction. The resultant syndromes include behavioural dementia, associative agnosia, semantic forms of primary progressive aphasia and semantic dementia. Clinicopathological correlations show that object naming and word comprehension are critically dependent on the language-dominant (usually left) temporopolar region, whereas behavioural control and non-verbal object recognition display a more bilateral representation with a rightward bias. Neuroanatomical experiments in macaques and neuroimaging in humans show that the temporoparietal region sits at the confluence of auditory, visual and limbic streams of processing at the downstream (deep) pole of the 'what' pathway. The functional neuroanatomy of this region revolves around three axes, an anterograde horizontal axis from unimodal to heteromodal and paralimbic cortex; a radial axis where visual (ventral), auditory (dorsal) and paralimbic (medial) territories encircle temporopolar cortex and display hemispheric asymmetry; and a vertical depth-of-processing axis for the associative elaboration of words, objects and interoceptive states. One function of this neural matrix is to support the transformation of object and word representations from unimodal percepts to multimodal concepts. The underlying process is likely to start at canonical gateways that successively lead to generic (superordinate), specific (basic) and unique levels of recognition. A first sign of left temporopolar dysfunction takes the form of taxonomic blurring where boundaries among categories are preserved but not boundaries among exemplars of a category. Semantic paraphasias and coordinate errors in word-picture verification tests are consequences of this phenomenon. Eventually, boundaries among categories are also blurred and comprehension impairments become more profound. The medial temporopolar region belongs to the amygdalocentric component of the limbic system and stands to integrate exteroceptive information with interoceptive states underlying social interactions. Review of the pertinent literature shows that word comprehension and conduct impairments caused by temporopolar strokes and temporal lobectomy are far less severe than those seen in temporopolar atrophies. One explanation for this unexpected discrepancy invokes the miswiring of residual temporopolar neurons during the many years of indolently progressive neurodegeneration. According to this hypothesis, the temporopolar regions become not only dysfunctional but also sources of aberrant outputs that interfere with the function of areas elsewhere in the language and paralimbic networks, a juxtaposition not seen in lobectomy or stroke.

Specific disruption of the ventral anterior temporo-frontal network reveals key implications for language comprehension and cognition

Recent investigations have raised the question of the role of the anterior lateral temporal cortex in language processing (ventral language network). Here we present the language and overall cognitive performance of a rare male patient with chronic middle cerebral artery cerebrovascular accident with a well-documented lesion restricted to the anterior temporal cortex and its connections via the extreme capsule with the pars triangularis of the inferior frontal gyrus (i.e. Broca’s region). The performance of this unique patient is compared with that of two chronic middle cerebral artery cerebrovascular accident male patients with damage to the classic dorsal posterior temporo-parietal language system. Diffusion tensor imaging is used to reconstruct the relevant white matter tracts of the three patients, which are also compared with those of 10 healthy individuals. The patient with the anterior temporo-frontal lesion presents with flawless and fluent speech, but selective impairment in accessing lexico-semantic information, in sharp contrast to the impairments in speech, sentence comprehension and repetition observed after lesions to the classic dorsal language system. The present results underline the contribution of the ventral language stream in lexico-semantic processing and higher cognitive functions, such as active selective controlled retrieval.

Neuropsychological profiling and clinical DTI of three stroke patients highlight the importance of the ventral language system in normal language comprehension and cognition.

Enhanced positive emotional reactivity in frontotemporal dementia reflects left-lateralized atrophy in the temporal and frontal lobes

In frontotemporal dementia (FTD), left-lateralized atrophy patterns have been associated with elevations in certain positive emotions. Here, we investigated whether positive emotional reactivity was enhanced in semantic variant primary progressive aphasia (svPPA), an FTD syndrome that targets the left anterior temporal lobe. Sixty-one participants (16 people with svPPA, 24 people with behavioral variant FTD, and 21 healthy controls) viewed six 90-sec trials that were comprised of a series of photographs; each trial was designed to elicit a specific positive emotion, negative emotion, or no emotion. Participants rated their positive emotional experience after each trial, and their smiling behavior was coded with the Facial Action Coding System. Results indicated that positive emotional experience and smiling were elevated in svPPA in response to numerous affective and non-affective stimuli. Voxel-based morphometry analyses revealed that greater positive emotional experience and greater smiling in the patients were both associated with smaller gray matter volume in the left superior temporal gyrus (pFWE < .05), among other left-lateralized frontotemporal regions. Whereas enhanced positive emotional experience related to atrophy in middle superior temporal gyrus and structures that promote cognitive control and emotion regulation, heightened smiling related to atrophy in posterior superior temporal gyrus and structures that support motor control. Our results suggest positive emotional reactivity is elevated in svPPA and offer new evidence that atrophy in left-lateralized emotion-relevant systems relates to enhanced positive emotions in FTD.

Neuropathological fingerprints of survival, atrophy and language in primary progressive aphasia

Primary progressive aphasia is a neurodegenerative disease that selectively impairs language without equivalent impairment of speech, memory or comportment. In 118 consecutive autopsies on patients with primary progressive aphasia, primary diagnosis was Alzheimer's disease neuropathological changes (ADNC) in 42%, corticobasal degeneration or progressive supranuclear palsy neuropathology in 24%, Pick's disease neuropathology in 10%, transactive response DNA binding proteinopathy type A [TDP(A)] in 10%, TDP(C) in 11% and infrequent entities in 3%. Survival was longest in TDP(C) (13.2 ± 2.6 years) and shortest in TDP(A) (7.1 ± 2.4 years). A subset of 68 right-handed participants entered longitudinal investigations. They were classified as logopenic, agrammatic/non-fluent or semantic by quantitative algorithms. Each variant had a preferred but not invariant neuropathological correlate. Seventy-seven per cent of logopenics had ADNC, 56% of agrammatics had corticobasal degeneration/progressive supranuclear palsy or Pick's disease and 89% of semantics had TDP(C). Word comprehension impairments had strong predictive power for determining underlying neuropathology positively for TDP(C) and negatively for ADNC. Cortical atrophy was smallest in corticobasal degeneration/progressive supranuclear palsy and largest in TDP(A). Atrophy encompassed posterior frontal but not temporoparietal cortex in corticobasal degeneration/progressive supranuclear palsy, anterior temporal but not frontoparietal cortex in TDP(C), temporofrontal but not parietal cortex in Pick's disease and all three lobes with ADNC or TDP(A). There were individual deviations from these group patterns, accounting for less frequent clinicopathologic associations. The one common denominator was progressive asymmetric atrophy overwhelmingly favouring the left hemisphere language network. Comparisons of ADNC in typical amnestic versus atypical aphasic dementia and of TDP in type A versus type C revealed fundamental biological and clinical differences, suggesting that members of each pair may constitute distinct clinicopathologic entities despite identical downstream proteinopathies. Individual TDP(C) participants with unilateral left temporal atrophy displayed word comprehension impairments without additional object recognition deficits, helping to dissociate semantic primary progressive aphasia from semantic dementia. When common and uncommon associations were considered in the set of 68 participants, one neuropathology was found to cause multiple clinical subtypes, and one subtype of primary progressive aphasia to be caused by multiple neuropathologies, but with different probabilities. Occasionally, expected clinical manifestations of atrophy sites were absent, probably reflecting individual peculiarities of language organization. The hemispheric asymmetry of neurodegeneration and resultant language impairment in primary progressive aphasia reflect complex interactions among the cellular affinities of the degenerative disease, the constitutive biology of language cortex, familial or developmental vulnerabilities of this network and potential idiosyncrasies of functional anatomy in the affected individual.

White matter abnormalities associated with ADHD outcomes in adulthood

It remains unclear if previously reported structural abnormalities in children with ADHD are present in adulthood regardless of clinical outcome. In this study, we examined the extent to which focal-rather than diffuse-abnormalities in fiber collinearity of 18 major white matter tracts could distinguish 126 adults with rigorously diagnosed childhood ADHD (ADHD; mean age [SD] = 34.3 [3.6] years; F/M = 12/114) from 58 adults without ADHD histories (non-ADHD; mean age [SD] = 33.9 [4.1] years; F/M = 5/53) and if any of these abnormalities were greater for those with persisting ADHD symptomatology. To this end, a tract profile approach was used. After accounting for age, sex, handedness, and comorbidities, a MANCOVA revealed a main effect of group (ADHD < non-ADHD; F_[18,155] = 2.1; p = 0.007) on fractional anisotropy (FA, a measure of fiber collinearity and/or integrity), in focal portions of white matter tracts involved in visuospatial processing and memory (i.e., anterior portion of the left inferior longitudinal fasciculus, and middle portion of the left and right cingulum angular bundle). Only abnormalities in the anterior portion of the left inferior longitudinal fasciculus distinguished probands with persisting versus desisting ADHD symptomatology, suggesting that abnormalities in the cingulum angular bundle might reflect "scarring" effects of childhood ADHD. To our knowledge, this is the first study using a tract profile approach to identify focal or widespread structural abnormalities in adults with ADHD rigorously diagnosed in childhood.

Transcranial Direct Current Stimulation Over the Right Anterior Temporal Lobe Does Not Modulate False Recognition

Non-invasive transcranial direct current stimulation (tDCS) over the left anterior temporal lobe (ATL) has been shown to cause a reduction in the rate of false memories with semantically related words. Such a reduction seems to be specific to false memories induced by the study of associative lists, but is not observed when the studied lists are categorical in nature. These findings are interpreted as evidence that the left ATL functions as an integration hub that is crucial for the binding of semantic information into coherent representations of concepts. In order to investigate whether the right ATL might also contribute to semantic integration in the processing of verbal associative material, a follow-up tDCS study was conducted with the stimulation at study lateralized on the right ATL. A sample of 75 undergraduate students participated in an experiment in which they studied 8 associative lists and 8 categorical lists. One third of the participants studied all their word lists under anodal stimulation, another third studied under cathodal stimulation and the other third under sham stimulation. Results showed that stimulation of the right ATL by tDCS does not modulate false recognition for either association-related critical words or category-related critical words. These results provide preliminary support to views positing asymmetric connectivity between the anterior temporal lobes and the semantic representational network, and provide evidence for understanding bilateral brain dynamics and the nature of semantically induced memory distortions.

The Impact of Right Temporal Lobe Epilepsy On Nonverbal Memory: Meta-regression of Stimulus- and Task-related Moderators

Nonverbal memory tests have great potential value for detecting the impact of lateralized pathology and predicting the risk of memory loss following right temporal lobe resection (TLR) for temporal lobe epilepsy (TLE) patients, but this potential has not been realized. Previous reviews suggest that stimulus type moderates the capacity of nonverbal memory tests to detect right-lateralized pathology (i.e., faces > designs), but the roles of other task-related factors have not been systematically explored. We address these limitations using mixed model meta-regression (k = 158) of right-lateralization effects (right worse than left TLE) testing the moderating effects of: 1) stimulus type (designs, faces, spatial), 2) learning format (single trial, repeated trials), 3) testing delay (immediate or long delay), and 4) testing format (recall, recognition) for three patient scenarios: 1) presurgical, 2) postsurgical, and 3) postsurgical change. Stimulus type significantly moderated the size of the right-lateralization effect (faces > designs) for postsurgical patients, test format moderated the size of the right-lateralization effect for presurgical-postsurgical change (recognition > recall) but learning format and test delay had no right-lateralization effect for either sample. For presurgical patients, none of the task-related factors significantly increased right-lateralization effects. This comprehensive review reveals the value of recognition testing in gauging the risk of nonverbal memory decline.

Functional Connectivity in Infancy and Toddlerhood Predicts Long-Term Language and Preliteracy Outcomes

Functional connectivity (FC) techniques can delineate brain organization as early as infancy, enabling the characterization of early brain characteristics associated with subsequent behavioral outcomes. Previous studies have identified specific functional networks in infant brains that underlie cognitive abilities and pathophysiology subsequently observed in toddlers and preschoolers. However, it is unknown whether and how functional networks emerging within the first 18 months of life contribute to the development of higher order, complex functions of language/literacy at school-age. This 5-year longitudinal imaging project starting in infancy, utilized resting-state functional magnetic resonance imaging and demonstrated prospective associations between FC in infants/toddlers and subsequent language and foundational literacy skills at 6.5 years old. These longitudinal associations were shown independently of key environmental influences and further present in a subsample of infant imaging data (≤12 months), suggesting early emerged functional networks specifically linked to high-order language and preliteracy skills. Moreover, emergent language skills in infancy and toddlerhood contributed to the prospective associations, implicating a role of early linguistic experiences in shaping the FC correlates of long-term oral language skills. The current results highlight the importance of functional organization established in infancy and toddlerhood as a neural scaffold underlying the learning process of complex cognitive functions.

Incidental Verbal Semantic Processing Recruits the Fronto-temporal Semantic Control Network

The frontoparietal semantic network, encompassing the inferior frontal gyrus and the posterior middle temporal cortex, is considered to be involved in semantic control processes. The explicit versus implicit nature of these control processes remains however poorly understood. The present study examined this question by assessing regional brain responses to the semantic attributes of an unattended stream of auditory words while participants' top-down attentional control processes were absorbed by a demanding visual search task. Response selectivity to semantic aspects of verbal stimuli was assessed via a functional magnetic resonance imaging response adaptation paradigm. We observed that implicit semantic processing of an unattended verbal stream recruited not only unimodal and amodal cortices in posterior supporting semantic knowledge areas, but also inferior frontal and posterior middle temporal areas considered to be part of the semantic control network. These results indicate that frontotemporal semantic networks support incidental semantic (control) processes.

White Matter Abnormalities Associated With Prolonged Recovery in Adolescents Following Concussion

Background: Concussion symptoms in adolescents typically resolve within 4 weeks. However, 20 - 30% of adolescents experience a prolonged recovery. Abnormalities in tracts implicated in visuospatial attention and emotional regulation (i.e., inferior longitudinal fasciculus, ILF; inferior fronto-occipital fasciculus, IFOF; uncinate fasciculus; UF) have been consistently reported in concussion; yet, to date, there are no objective markers of prolonged recovery in adolescents. Here, we evaluated the utility of diffusion MRI in outcome prediction. Forty-two adolescents (12.1 - 17.9 years; female: 44.0%) underwent a diffusion Magnetic Resonance Imaging (dMRI) protocol within the first 10 days of concussion. Based on days of injury until medical clearance, adolescents were then categorized into SHORT (<28 days; N = 21) or LONG (>28 days; N = 21) recovery time. Fractional anisotropy (FA) in the ILF, IFOF, UF, and/or concussion symptoms were used as predictors of recovery time (SHORT, LONG). Forty-two age- and sex-matched healthy controls served as reference. Higher FA in the ILF (left: adjusted odds ratio; AOR = 0.36, 95% CI = 0.15 - 0.91, P = 0.030; right: AOR = 0.28, 95% CI = 0.10 - 0.83, P = 0.021), IFOF (left: AOR = 0.21, 95% CI = 0.07 - 0.66, P = 0.008; right: AOR = 0.30, 95% CI = 0.11 - 0.83, P = 0.020), and UF (left: AOR = 0.26, 95% CI = 0.09 - 0.74, P = 0.011; right: AOR = 0.28, 95% CI = 0.10 - 0.73, P = 0.010) was associated with SHORT recovery. In additional analyses, while adolescents with SHORT recovery did not differ from HC, those with LONG recovery showed lower FA in the ILF and IFOF (P < 0.014). Notably, inclusion of dMRI findings increased the sensitivity and specificity (AUC = 0.93) of a prediction model including clinical variables only (AUC = 0.75). Our findings indicate that higher FA in long associative tracts (especially ILF) might inform a more objective and accurate prognosis for recovery time in adolescents following concussion.

The neural bases of resilient semantic system: evidence of variable neuro-displacement in cognitive systems

The purpose of this study was to explore an important research goal in cognitive and clinical neuroscience: What are the neurocomputational mechanisms that make cognitive systems "well engineered" and thus resilient across a range of performance demands and to mild levels of perturbation or even damage? A new hypothesis called 'variable neuro-displacement' suggests that cognitive systems are formed with dynamic, spare processing capacity, which balances energy consumption against performance requirements and can be resilient to changes in performance demands. Here, we tested this hypothesis by investigating the neural dynamics of the semantic system by manipulating performance demand. The performance demand was manipulated with two levels of task difficulty (easy vs. hard) in two different ways (stimulus type and response timing). We found that the demanding semantic processing increased regional activity in both the domain-specific semantic representational system (anterior temporal lobe) and the parallel executive control networks (prefrontal, posterior temporal, and parietal regions). Functional connectivity between these regions was also increased during demanding semantic processing and these increases were related to better semantic task performance. Our results suggest that semantic cognition is made resilient by flexible, dynamic changes including increased regional activity and functional connectivity across both domain-specific and domain-general systems. It reveals the intrinsic resilience-related mechanisms of semantic cognition, mimicking alterations caused by perturbation or brain damage. Our findings provide a strong implication that the intrinsic mechanisms of a well-engineered semantic system might be attributed to the compensatory functional alterations in the impaired brain.

The inferior longitudinal fasciculus: anatomy, function and surgical considerations

The inferior longitudinal fasciculus (ILF) is a large association white matter tract that interconnects, in a bidirectional manner, the occipital cortex to anterior temporal structures. In view of both its pattern of cortical projections and its recently evidenced multilayered anatomical organization, the ILF has been supposed to be vital for maintaining a wide range of cognitive and affective processes operating on the visual modality. As tumors commonly damage the temporal cortex, an updated knowledge of the functional anatomy of this ventral tract is needed to better map and monitor online its potential functions and thus to improve surgical outcomes. In this review, we first describe the gross anatomy of the ILF, its array of cortical terminations and its different layers. We then provide a comprehensive review of the functions that have been assigned to the tract. We successively address its role in object and face recognition, visual emotion recognition, language and semantic, including reading, and memory. It is especially shown that the ILF is critically involved in visually-guided behaviors, as its breakdown, both in sudden neurosurgical and progressive neurodegenerative diseases, is commonly associated with visual-specific neuropsychological syndromes (e.g. prosopagnosia and pure alexia, and so on). In the last section, we discuss the extent to which the ILF can reorganize in response to glioma infiltration and to surgery, and provide some reflections on how its intra-operative mapping may be refined.

Autobiographical memory in epileptic patients after temporal lobe resection or bitemporal hippocampal sclerosis

The human hippocampus is believed to be a crucial node in the neural network supporting autobiographical memory retrieval. Structural mesial temporal damage associated with temporal lobe epilepsy (TLE) provides an opportunity to systematically investigate and better understand the local and distal functional consequences of mesial temporal damage in the engagement of the autobiographical memory network. We examined 19 TLE patients (49.21 ± 11.55 years; 12 females) with unilateral mesial TLE (MTLE; 12 with anterior temporal lobe resection: 6 right MTLE, 6 left MTLE) or bilateral mesial TLE (7 BMTLE) and 18 matched healthy subjects. We used functional MRI (fMRI) with an adapted autobiographical memory paradigm and a specific neuropsychological test (Autobiographical Memory Interview, AMI). While engaged in the fMRI autobiographical memory paradigm, all groups activated a large fronto-temporo-parietal network. However, while this network was left lateralized for healthy participants and right MTLE patients, left MTLE and patients with BMTLE also showed strong activation in right temporal and frontal regions. Moreover, BMTLE and left MTLE patients also showed significant mild deficits in episodic autobiographical memory performance measured with the AMI test. The right temporal and extra-temporal fMRI activation, along with the impairment in autobiographical memory retrieval found in left MTLE and BMTLE patients suggest that alternate brain areas-other than the hippocampus-may also support this process, possibly due to neuroplastic effects.

The Language Network Is Recruited but Not Required for Nonverbal Event Semantics

The ability to combine individual concepts of objects, properties, and actions into complex representations of the world is often associated with language. Yet combinatorial event-level representations can also be constructed from nonverbal input, such as visual scenes. Here, we test whether the language network in the human brain is involved in and necessary for semantic processing of events presented nonverbally. In Experiment 1, we scanned participants with fMRI while they performed a semantic plausibility judgment task versus a difficult perceptual control task on sentences and line drawings that describe/depict simple agent-patient interactions. We found that the language network responded robustly during the semantic task performed on both sentences and pictures (although its response to sentences was stronger). Thus, language regions in healthy adults are engaged during a semantic task performed on pictorial depictions of events. But is this engagement necessary? In Experiment 2, we tested two individuals with global aphasia, who have sustained massive damage to perisylvian language areas and display severe language difficulties, against a group of age-matched control participants. Individuals with aphasia were severely impaired on the task of matching sentences to pictures. However, they performed close to controls in assessing the plausibility of pictorial depictions of agent-patient interactions. Overall, our results indicate that the left frontotemporal language network is recruited but not necessary for semantic processing of nonverbally presented events.

Chinese-English bilinguals show linguistic-perceptual links in the brain associating short spoken phrases with corresponding real-world natural action sounds by semantic category

Higher cognitive functions such as linguistic comprehension must ultimately relate to perceptual systems in the brain, though how and why this forms remains unclear. Different brain networks that mediate perception when hearing real-world natural sounds has recently been proposed to respect a taxonomic model of acoustic-semantic categories. Using functional magnetic resonance imaging (fMRI) with Chinese/English bilingual listeners, the present study explored whether reception of short spoken phrases, in both Chinese (Mandarin) and English, describing corresponding sound-producing events would engage overlapping brain regions at a semantic category level. The results revealed a double-dissociation of cortical regions that were preferential for representing knowledge of human versus environmental action events, whether conveyed through natural sounds or the corresponding spoken phrases depicted by either language. These findings of cortical hubs exhibiting linguistic-perceptual knowledge links at a semantic category level should help to advance neurocomputational models of the neurodevelopment of language systems.

Nosology of Primary Progressive Aphasia and the Neuropathology of Language

Primary progressive aphasia (PPA) is a dementia syndrome associated with several neuropathologic entities, including Alzheimer's disease (AD) and all major forms of frontotemporal lobar degeneration (FTLD). It is classified into subtypes defined by the nature of the language domain that is most impaired. The asymmetric neurodegeneration of the hemisphere dominant for language (usually left) is one consistent feature of all PPA variants. This feature offers unique opportunities for exploring mechanisms of selective vulnerability in neurodegenerative diseases and the neuroanatomy of language. This chapter reviews some of the current trends in PPA research as well as the challenges that remain to be addressed on the nosology, clinicopathologic correlations, and therapy of this syndrome.

Contributions of left and right anterior temporal lobes to semantic cognition: Evidence from patients with small temporopolar lesions

Decades of research have increased the understanding of the contribution of the anterior temporal lobes (ATLs) to semantic cognition. Nonetheless, whether semantic processing of different types of information show a selective relationship with left and right ATLs, or whether semantic processing in the ATLs is independent of the modality of the input is currently unknown. There exists evidence supporting each of these alternatives. A fundamental objection to these findings is that they were obtained from studies with patients with brain damage affecting extensive regions, sometimes bilaterally. In the current study, we assessed a group of 38 temporal lobe epilepsy (TLE) patients with either left or right small epileptogenic lesions with a battery of commonly used semantic tasks that tested verbal and non-verbal semantic processing. We found that left TLE patients exhibited worse performance than controls on the verbal semantic tasks, as expected, but also on the non-verbal semantic task. On the other hand, performance of the right TLE group did not differ from controls on the non-verbal task, but was worse on a semantic fluency task. When performance between patient groups was compared, we found that left TLE not only did worse than right TLE on the naming task, but also on the non-verbal associative memory task. When considered together, current data do not support a strong view of input modality differences between left and right ATLs. Additionally, they provide evidence indicating that the left and right ATLs do not make similar contributions to a singular functional system for semantic representation.

A unified neurocomputational bilateral model of spoken language production in healthy participants and recovery in poststroke aphasia

Studies of healthy and impaired language have generated many verbally described hypotheses. While these verbal descriptions have advanced our understanding of language processing, some explanations are mutually incompatible, and it is unclear how they work mechanistically. We constructed a neurocomputational bilateral model of spoken language production to simulate a range of phenomena in healthy participants and patients with aphasia simultaneously, including language lateralization, impaired performance after left but not right damage, and hemispheric involvement in plasticity-dependent recovery. The model demonstrates how seemly contradictory findings can be simulated within a single framework. This provides a coherent mechanistic account of language lateralization and recovery from poststroke aphasia.

Understanding the processes underlying normal, impaired, and recovered language performance has been a long-standing goal for cognitive and clinical neuroscience. Many verbally described hypotheses about language lateralization and recovery have been generated. However, they have not been considered within a single, unified, and implemented computational framework, and the literatures on healthy participants and patients are largely separated. These investigations also span different types of data, including behavioral results and functional MRI brain activations, which augment the challenge for any unified theory. Consequently, many key issues, apparent contradictions, and puzzles remain to be solved. We developed a neurocomputational, bilateral pathway model of spoken language production, designed to provide a unified framework to simulate different types of data from healthy participants and aphasic patients. The model encapsulates key computational principles (differential computational capacity, emergent division of labor across pathways, experience-dependent plasticity-related recovery) and provides an explanation for the bilateral yet asymmetric lateralization of language in healthy participants, chronic aphasia after left rather than right hemisphere lesions, and the basis of partial recovery in patients. The model provides a formal basis for understanding the relationship between behavioral performance and brain activation. The unified model is consistent with the degeneracy and variable neurodisplacement theories of language recovery, and adds computational insights to these hypotheses regarding the neural machinery underlying language processing and plasticity-related recovery following damage.

The right anterior temporal lobe critically contributes to magnitude knowledge

Cognitive estimation is a mental ability applied to solve numerical problems when precise facts are unknown, unavailable or impractical to calculate. It has been associated with several underlying cognitive components, most often with executive functions and semantic memory. Little is known about the neural correlates of cognitive estimation. To address this issue, the present cross-sectional study applied lesion-symptom mapping in a group of 55 patients with left hemineglect due to right-hemisphere stroke. Previous evidence suggests a high prevalence of cognitive estimation impairment in these patients, as they might show a general bias towards large magnitudes. Compared to 55 age- and gender-matched healthy controls, the patient group demonstrated impaired cognitive estimation. However, the expected large magnitude bias was not found. Lesion-symptom mapping related their general estimation impairment predominantly to brain damage in the right anterior temporal lobe. Also critically involved were the right uncinate fasciculus, the anterior commissure and the right inferior frontal gyrus. The main findings of this study emphasize the role of semantic memory in cognitive estimation, with reference to a growing body of neuroscientific literature postulating a transmodal hub for semantic cognition situated in the bilateral anterior temporal lobe. That such semantic hub function may also apply to numerical knowledge is not undisputed. We here propose a critical contribution of the right anterior temporal lobe to at least one aspect of number processing, i.e. the knowledge about real-world numerical magnitudes.

The semantic storage loss score: An Algorithm for measuring an individual's level of semantic storage loss due to temporal lobe damage in neurodegenerative disease

Anomia is common in Primary Progressive Aphasia (PPA), and there is considerable evidence that semantic problems (as opposed to impaired access to output word phonology) exist in many PPA individuals irrespective of their strict subtype, including a loss of representations from semantic memory, which is typical for people with the semantic variant of PPA. In this manuscript we present a straightforward novel clinical algorithm that quantifies this degree of semantic storage impairment. We sought to produce an algorithm by employing tasks that would measure key elements of semantic storage loss: a) whether an unrecalled name could be retrieved with cues; b) if performance for items was consistent across tasks; and c) the degree to which a participant’s performance was related to general severity of cognitive impairment rather than semantic loss. More specifically, these tasks were given to 28 individuals with PPA (12 participants had a clinical diagnosis of atypical Alzheimer’s Disease with the logopenic variant of PPA; the remaining 16 participants received a clinical diagnosis of Frontotemporal dementia (11 were classified as the non-fluent variant of PPA and five were the semantic variant of PPA). Scores from these tasks produced a single omnibus semantic memory storage loss score (SSL score) for each person that ranged from 0.0 to 1.0, with scores closer to 0 more indicative of semantic storage loss. Indeed, supporting the hypothesis that our scores measure the degree of semantic storage loss, we found participants with the semantic variant of PPA had the lowest scores, and SSL scores could predict the degree of hypometabolism in the anterior temporal lobe; even when only people with the logopenic variant of PPA were examined. Thus, these scores show promise quantitating the degree of a person’s semantic representation loss.

Impaired naming performance in temporal lobe epilepsy: language fMRI responses are modulated by disease characteristics

OBJECTIVE

To investigate alterations of language networks and their relation to impaired naming performance in temporal lobe epilepsy (TLE) using functional MRI.

METHODS

Seventy-two adult TLE patients (41 left) and 36 controls were studied with overt auditory and picture naming fMRI tasks to assess temporal lobe language areas, and a covert verbal fluency task to probe frontal lobe language regions. Correlation of fMRI activation with clinical naming scores, and alteration of language network patterns in relation to epilepsy duration, age at onset and seizure frequency, were investigated with whole-brain multiple regression analyses.

RESULTS

Auditory and picture naming fMRI activated the left posterior temporal lobe, and stronger activation correlated with better clinical naming scores. Verbal fluency MRI mainly activated frontal lobe regions. In left and right TLE, a later age of epilepsy onset related to stronger temporal lobe activations, while earlier age of onset was associated with impaired deactivation of extratemporal regions. In left TLE patients, longer disease duration and higher seizure frequency were associated with reduced deactivation. Frontal lobe language networks were unaffected by disease characteristics.

CONCLUSIONS

While frontal lobe language regions appear spared, temporal lobe language areas are susceptible to dysfunction and reorganisation, particularly in left TLE. Early onset and long duration of epilepsy, and high seizure frequency, were associated with compromised activation and deactivation patterns of task-associated regions, which might account for impaired naming performance in individuals with TLE.

Temporopolar amygdalohippocampectomy: seizure control and postoperative outcomes

OBJECTIVE

The objective of this study was to evaluate the efficacy and safety of a modified surgical approach for the treatment of temporal lobe epilepsy secondary to hippocampal sclerosis (HS). This modified approach, called temporopolar amygdalohippocampectomy (TP-AH), includes a transsylvian resection of the temporal pole and subsequent amygdalohippocampectomy utilizing the limen insula as an anatomical landmark.

METHODS

A total of 61 patients who were diagnosed with HS and underwent TP-AH between 2013 and 2017 were enrolled. Patients performed pre- and postoperative diffusion tensor imaging and were classified according to Engel's scale for seizure control. To evaluate the functional preservation of the temporal stem white-matter fiber tracts, the authors analyzed postoperative Humphrey perimetries and pre- and postoperative neurocognitive performance (Rey Auditory Verbal Learning Test [RAVLT], Weschler Memory Scale-Revised [WMS-R], intelligence quotient [IQ], Boston Naming Test [BNT], and semantic and phonemic fluency). Demographic data and surgical complications were also recorded and described.

RESULTS

After a median follow-up of 36 ± 16 months, 46 patients (75.4%) achieved Engel class I, of whom 37 (60.6%) were Engel class IA. No significant changes in either the inferior frontooccipital fasciculus and optic radiation tractography were observed postoperatively for both left- and right-side surgeries. Reliable perimetry was obtained in 40 patients (65.6%), of whom 27 (67.5%) did not present any visual field defects (VFDs) attributable to surgery, while 12 patients (30%) presented with quadrant VFD, and 1 patient (2.5%) presented with hemifield VFD. Despite a significant decline in verbal memory (p = 0.007 for WMS-R, p = 0.02 for RAVLT recognition), there were significant improvements in both IQ (p < 0.001) and visual memory (p = 0.007). Semantic and phonemic fluency, and scores on the BNT, did not change postoperatively.

CONCLUSIONS

TP-AH provided seizure control similar to historical temporal lobe approaches, with a tendency to preserve the temporal stem and a satisfactory incidence of VFD. Despite a significant decline in verbal memory, there were significant improvements in both IQ and visual memory, along with preservation of executive function. This approach can be considered a natural evolution of the selective transsylvian approach.

A case of TDP-43 type C pathology presenting as nonfluent variant primary progressive aphasia

We report a case of rapidly progressive nonfluent variant PPA (nfvPPA), age at onset 77 years old and disease duration 3.3 years, who came to post mortem and was found to have TDP-43 type C pathology, an unusual finding for nfvPPA. All prior TDP-43 type C cases from the UCL FTD cohort (n=25) had a semantic variant PPA (svPPA) phenotype, with all having a younger age at onset and longer disease duration than the nfvPPA case. Volumetric analysis of MRI from the nfvPPA case, twelve of the svPPA cases and ten age-matched controls was performed. Whilst left frontal and insular volumes were lower in the nfvPPA case compared with svPPA, cortical and medial temporal lobe volumes were lower (particularly on the right) in the svPPA group compared with the nfvPPA patient. Such anatomical involvement is likely to be consistent with the presence of a nonfluent aphasia (left frontal lobe and insula), and only mild semantic deficit early in the illness (left but not right temporal lobe). Such unique cases add to the heterogeneity of the FTD spectrum.

Group membership dictates the neural correlates of social optimism biases

Optimism bias, i.e. expecting the future to hold more desirable than undesirable outcomes, also extends to people that we like or admire. However, it remains unknown how the brain generates this social optimism bias. In this study, respondents estimated the likelihood of future desirable and undesirable outcomes for an in-group and three out-groups: warm-incompetent, cold-competent, and cold-incompetent. We found a strong social optimism bias for the in-group and the warm out-group and an inverted pattern for the cold-incompetent out-group. For all groups, scores of social optimism bias correlated with the brain activity in structures that respondents differentially engaged depending on the target social group. In line with our hypotheses, evaluating the in-group recruited the ventromedial prefrontal cortex and the precuneus/posterior cingulate cortex, whereas evaluating the warm out-group engaged the posterior insula, mid cingulate cortex, and somatosensory cortices. These findings suggest different underlying cognitive mechanisms of social optimism bias for these groups, despite similar behavioural patterns. Thinking about the cold out-groups recruited the right anterior temporal lobe, and temporoparietal junction. Evaluating the cold-incompetent out-group additionally recruited the anterior insula, inferior frontal cortex and dorsomedial frontal cortex. We discuss these neuroimaging findings with respect to their putative cognitive functions.

Efecto de concretud inverso en Afasia Progresiva Primaria-variante semántica: Estudio longitudinal de un paciente

La Afasia Progresiva Primaria (APP) es una patología neurodegenerativa que se presenta con afectación insidiosa y progresiva del lenguaje. Los criterios diagnósticos actuales diferencian tres subtipos de APP, cada una con perfiles neurolingüísticos específicos. Diversas investigaciones han propuesto que un síntoma característico de la APP variante semántica (APP-vs) es un mayor compromiso en el procesamiento de conceptos concretos que de abstractos (Efecto de Concretud Inverso - ECI). Para explicar este ECI se han propuesto diferentes explicaciones: (a). el patrón de compromiso neural, (b). el nivel educativo de los pacientes, (c). el estadio de la enfermedad. El objetivo del presente trabajo es estudiar en forma longitudinal la progresión en el procesamiento de conceptos concretos y abstractos en un paciente diagnosticado con APP-vs. Para ello se utilizó una tarea de juicios de sinonimia donde se debe identificar si dos palabras son sinónimos o no. La tarea cuenta con pares de conceptos concretos y abstractos. Se evaluó al paciente en tres momentos (2014, 2015 y 2016). Se observó un mejor desempeño de conceptos abstractos en la primera evaluación. El ECI desaparece en la segunda evaluación. El patrón se revierte en la tercera. Estos resultados apoyan la propuesta de que el ECI observado en pacientes con APP-vs es un síntoma de los estadios iniciales de la enfermedad. Este ECI se relacionaría con la afectación temprana de las porciones del Lóbulo Temporal Anterior que procesan rasgos visuales, que serían más relevantes para los conceptos concretos.

Primary Progressive Aphasia and Stroke Aphasia

PURPOSE OF REVIEW

This article summarizes the clinical and anatomic features of the three named variants of primary progressive aphasia (PPA): semantic variant PPA, nonfluent/agrammatic variant PPA, and logopenic variant PPA. Three stroke aphasia syndromes that resemble the PPA variants (Broca aphasia, Wernicke aphasia, and conduction aphasia) are also presented.

RECENT FINDINGS

Semantic variant PPA and Wernicke aphasia are characterized by fluent speech with naming and comprehension difficulty; these syndromes are associated with disease in different portions of the left temporal lobe. Patients with nonfluent/agrammatic variant PPA or Broca aphasia have nonfluent speech with grammatical difficulty; these syndromes are associated with disease centered in the left inferior frontal lobe. Patients with logopenic variant PPA or conduction aphasia have difficulty with repetition and word finding in conversational speech; these syndromes are associated with disease in the left inferior parietal lobe. While PPA and stroke aphasias resemble one another, this article also presents their distinguishing features.

SUMMARY

Primary progressive and stroke aphasia syndromes interrupt the left perisylvian language network, resulting in identifiable aphasic syndromes.

Identification of taxonomic and thematic relationships: Do the two semantic systems have the same status in semantic dementia?

Introduction: Disequilibrium between the taxonomic and thematic semantic systems was previously hypothesized in participants with semantic dementia (SD), without rigorously assessing their ability to identify the two types of semantic relationships. Therefore, the aim of the present study was to directly compare the ability of 10 participants with SD, 10 participants with Alzheimer's disease (AD), and 20 controls to identify thematic versus taxonomic relationships. Methods: Participants performed an explicit forced-choice picture-matching task in which they had to determine which of two pictures of choice was semantically related to the target picture. Target pictures could display natural or artifact objects. Each target was presented once with a taxonomically related picture and once with a thematically related picture. Results: Analyses of correct thematic and taxonomic matches as a function of target domain showed that the performance of the two groups of patients differed in the taxonomic conditions but not in the thematic conditions, demonstrating a relative preservation of thematic knowledge in SD. Additional correlation analyses further indicated that the particular status of thematic relationships in SD was even stronger for artifact concepts. Conclusions: Results provide evidence of the heterogeneous nature of semantic knowledge disruption in SD, and could be regarded as being consistent with the existence of two neuroanatomically and functionally distinct semantic systems. Results further stress the relevance of performing a more detailed and complete assessment of semantic performance in participants with SD, in order to capture the impaired but also preserved aspects of their knowledge.

Attention Deficits in Stroke Patients: The Role of Lesion Characteristics, Time from Stroke, and Concomitant Neuropsychological Deficits

Attention impairments are frequent in stroke patients with important consequences on the rehabilitation outcomes and quality of life. The aim of the study was to perform a comprehensive assessment of selective and intensive attention processes in a large population of brain-damaged patients, evaluating the influence of the side and site of the brain lesion, the time from stroke, and the concomitant presence of aphasia or neglect. We assessed 204 patients with a first unilateral brain lesion and 42 healthy individuals with three subtests of the Test of Attentional Performance (TAP): Alertness, Go-No Go, and Divided Attention. 44.4% of patients had an impairment in both intensive and selective aspects of attention, 5.6% had deficits only in the intensive component, and 31.8% had deficits only in selective tasks. More than 80% of the patients fell below the cut-off point on at least one task. Patients with a right hemispheric lesion (RHL) were more impaired than patients with a left hemispheric lesion (LHL) especially in tonic and phasic alertness. Patients with total anterior infarcts (TACI) presented the worst profile compared to other stroke subtypes, with a difference between total and lacunar subtypes in the Alertness test, independent of the presence of warning. Patients in the chronic phase had shorter RTs than acute patients only in the Alertness test. In patients with LHL, the presence of aphasia was associated with a greater deficit in selective attention. In patients with RHL, the presence of unilateral neglect was associated with impaired alertness and selective attention. Attention deficits are common after a unilateral first stroke. In keeping with the hierarchical organization of attention functions, results confirm the important role of the right hemisphere for the intensive components of attention, also highlighting the involvement of left hemisphere functioning for the selective aspects, possibly indicating a role of its linguistic functions.

Morphometric correlates of anomia in patients with small left temporopolar lesions

Visual object naming is a complex cognitive process that engages an interconnected network of cortical regions moving from occipitotemporal to anterior-inferior temporal cortices, and extending into the inferior frontal cortex. Naming can fail for diverse reasons, and different stages of the naming multi-step process appear to be reliant upon the integrity of different neuroanatomical locations. While the neural correlates of semantic errors have been extensively studied, the neural basis of omission errors remains relatively unspecified. Although a strong line of evidence supports an association between anterior temporal lobe damage and semantic errors, there are some studies suggesting that the anterior temporal lobe could be also associated with omissions. However, support for this hypothesis comes from studies with patients in whom damage affected extensive brain regions, sometimes bilaterally. Here, we availed of a group of 12 patients with epilepsy associated with a small lesion at the tip of the left temporal pole. Using an unbiased surface-based morphometry methodology, we correlated two morphological features with errors observed during visual naming. Analyses revealed a correlation between omission errors and reduced local gyrification index in three cortical clusters: one in the left anteromedial temporal lobe region (AMTL) and two in the left anterior cingulate cortex (ACC). Our findings support the view that regions in ACC and AMTL are critical structures within a network engaged in word selection from semantics.

Increased activation in the left ventrolateral prefrontal cortex and temporal pole during tonality change in music

In human music, the tonality (key) may change to punctuate sectional structures and to produce emotional effects. A tonality change would sound "smoother" when it is supported by appropriate harmony. This functional magnetic resonance imaging study examined the neural substrates of the processing of tonality change. We used a 2 × 2 factorial design with factors tonality change (tonality changed versus tonality unchanged) and harmonization (harmonized versus unharmonized). Participants were asked to covertly sing the pitch names in the movable-do system along with the heard melody. Repetitions of this melody were associated with or without a tonality change, with equal probability in a pseudo-random order. Our result demonstrated that tonality changes elicited increased activation in the left ventrolateral prefrontal cortex and left temporal pole. When a tonality change occurred, the left ventrolateral prefrontal cortex might underpin the cognitive control for retrieving the pitch-naming rule of the new tonality, whereas the left temporal pole might integrate the melodic/harmonic context and emotional meanings of music. This study provides a new insight into the cognitive and emotional processing of music.

Knowledge of language function and underlying neural networks gained from focal seizures and epilepsy surgery

The effects of epilepsy and its treatments have contributed significantly to language models. The setting of epilepsy surgery, which allows for careful pre- and postsurgical evaluation of patients with cognitive testing and neuroimaging, has produced a wealth of language findings. Moreover, a new wave of surgical interventions, including stereotactic laser ablation and radio frequency ablation, have contributed new insights and corrections to language models as they can make extremely precise, focal lesions. This review covers the common language deficits observed in focal dyscognitive seizure syndromes. It also addresses the effects of surgical interventions on language, and highlights insights gained from unique epilepsy assessment methods (e.g., cortical stimulation mapping, Wada evaluation). Emergent findings are covered including a lack of involvement of the hippocampus in confrontation word retrieval, possible roles for key white matter tracts in language, and the often-overlooked basal temporal language area. The relationship between language and semantic memory networks is also explored, with brief consideration given to the prevailing models of semantic processing, including the amodal Hub and distributed, multi-modal processing models.

What happens when nothing happens? An investigation of pauses as a compensatory mechanism in early Alzheimer's disease

Lexical-semantic impairment is one of the earliest symptoms of Alzheimer's disease (AD) and is usually examined by single word processing tasks. During speech production, pauses are often investigated as a hallmark of a patient's lexical-semantic decline. In the current study, we put forward the hypothesis that pauses reflect different processes according to the type of discourse. We believe that lexical and semantic impairment would predict a patient's pause frequency in a picture-based narrative (PBN) while anterograde memory would predict a patient's pause frequency in a memory-based narrative (MBN). To demonstrate this, we recruited 17 early AD patients and 17 matched controls. They underwent a full neuropsychological and language assessment and two narrative production assessments. We compared pause duration and frequency in the AD participants' and healthy controls' PBN and MBN. A multiple regression model was used in each narrative and in each group individually to assess the relationship between cognitive processes and pause frequency. Our results show that participants with AD produced more pauses in the PBN only. The frequency was predicted by semantic fluency performance with which it was positively correlated, contrary to what was expected. In the MBN, pause frequency in the AD participants was positively correlated with and predicted by their memory performance. We then examined the neuroanatomical correlates of pause frequency in the AD participants. Considering the PBN, pause frequency was also positively correlated with the grey matter density of the anterior temporal lobe. These findings suggest that patients use pauses as compensatory mechanisms in the earliest stages of AD. Pauses therefore may reflect the time required for the compensation and the realisation of a weak process depending on the narrative task and should be considered as a positive sign.

Right temporal alpha oscillations as a neural mechanism for inhibiting obvious associations

Creative cognition requires mental exploration of remotely connected concepts while suppressing dominant ones. Across four experiments using different samples of participants, we provide evidence that right temporal alpha oscillations play a crucial role in inhibiting habitual thinking modes, thereby paving the way for accessing more remote ideas. In the first experiment, participants completed the compound remote associate task (RAT) in three separate sessions: during right temporal alpha (10 Hz) transcranial alternating current brain stimulation (tACS), left temporal alpha tACS, and sham tACS. Participants performed better under right tACS only on RAT items in which two of the three words shared misleading semantic associations. In the second experiment, we measured EEG while the participants solved RAT items with or without shared misleading associations. We observed an increase in right temporal alpha power when participants correctly solved RAT items with misleading semantic associations. The third experiment demonstrated that while solving divergent thinking tasks participants came up with more remote ideas when stimulated by right temporal alpha tACS. In the fourth experiment, we found that participants showed higher right temporal alpha power when generating more remote uses for common objects. These studies altogether indicate that right temporal alpha oscillations may support creativity by acting as a neural mechanism for an active inhibition of obvious semantic associations.

Avaliação Neuropsicológica em Pacientes com Tumores Cerebrais: revisão sistemática da literatura

Os tumores cerebrais (TC) são causados pelo crescimento anormal de células. As consequências dos TC podem envolver prejuízos físicos, cognitivos e emocionais. Objetiva-se identificar e descrever os prejuízos cognitivos associados aos TC, através de uma revisão sistemática da literatura. As buscas realizaram-se nas bases de dados internacionais PubMed/MEDLINE, LILACS, e SCOPUS, incluindo abstracts de artigos publicados de 2006 a 2016. Encontrou-se 501 artigos desses, 31 cumpriram os critérios de inclusão. Os TC, representam 5% das neoplasias, sendo alguns mais agressivos que outros. Apresenta-se como sintomas severos: déficits cognitivos, motores. A avaliação neuropsicológica auxilia na identificação de possíveis alterações cognitivas e no acompanhamento dos efeitos do tratamento, contribuindo para melhor qualidade de vida desses pacientes. Os resultados encontrados indicaram as Escalas Wechsler de Inteligência; Matrizes Progressivas de Raven, Figuras Complexas de Rey, Teste de Retenção Visual de Benton, e Token Test como os mais utilizados, e que evidenciaram como prejuízos os envolvendo a memória, a atenção e funções executivas. A localização mais frequente destes TC eram as regiões frontais e temporais e os gliomas o tipo de tumor mais investigado.

Functional Anatomy of the Inferior Longitudinal Fasciculus: From Historical Reports to Current Hypotheses

The inferior longitudinal fasciculus (ILF) is a long-range, associative white matter pathway that connects the occipital and temporal-occipital areas of the brain to the anterior temporal areas. In view of the ILF's anatomic connections, it has been suggested that this pathway has a major role in a relatively large array of brain functions. Until recently, however, the literature data on these potential functions were scarce. Here, we review the key findings of recent anatomic, neuromodulation, and neuropsychological studies. We also summarize reports on how this tract is disrupted in a wide range of brain disorders, including psychopathologic, neurodevelopmental, and neurologic diseases. Our review reveals that the ILF is a multilayered, bidirectional tract involved in processing and modulating visual cues and thus in visually guided decisions and behaviors. Accordingly, sudden disruption of the ILF by neurologic insult is mainly associated with neuropsychological impairments of visual cognition (e.g., visual agnosia, prosopagnosia, and alexia). Furthermore, disruption of the ILF may constitute the pathophysiologic basis for visual hallucinations and socio-emotional impairments in schizophrenia, as well as emotional difficulties in autism spectrum disorder. Degeneration of the ILF in neurodegenerative diseases affecting the temporal lobe may explain (at least in part) the gradual onset of semantic and lexical access difficulties. Although some of the functions mediated by the ILF appear to be relatively lateralized, observations from neurosurgery suggest that disruption of the tract's anterior portion can be dynamically compensated for by the contralateral portion. This might explain why bilateral disruption of the ILF in either acute or progressive disease is highly detrimental in neuropsychological terms.

Revealing the Dynamic Modulations That Underpin a Resilient Neural Network for Semantic Cognition: An fMRI Investigation in Patients With Anterior Temporal Lobe Resection

One critical feature of any well-engineered system is its resilience to perturbation and minor damage. The purpose of the current study was to investigate how resilience is achieved in higher cognitive systems, which we explored through the domain of semantic cognition. Convergent evidence implicates the bilateral anterior temporal lobes (ATLs) as a conceptual knowledge hub. While bilateral damage to this region produces profound semantic impairment, unilateral atrophy/resection or transient perturbation has a limited effect. Two neural mechanisms might underpin this resilience to unilateral ATL damage: 1) the undamaged ATL upregulates its activation in order to compensate; and/or 2) prefrontal regions involved in control of semantic retrieval upregulate to compensate for the impoverished semantic representations that follow from ATL damage. To test these possibilities, 34 postsurgical temporal lobe epilepsy patients and 20 age-matched controls were scanned whilst completing semantic tasks. Pictorial tasks, which produced bilateral frontal and temporal activation, showed few activation differences between patients and control participants. Written word tasks, however, produced a left-lateralized activation pattern and greater differences between the groups. Patients with right ATL resection increased activation in left inferior frontal gyrus (IFG). Patients with left ATL resection upregulated both the right ATL and right IFG. Consistent with recent computational models, these results indicate that 1) written word semantic processing in patients with ATL resection is supported by upregulation of semantic knowledge and control regions, principally in the undamaged hemisphere, and 2) pictorial semantic processing is less affected, presumably because it draws on a more bilateral network.

Semantic representation in the white matter pathway

Object conceptual processing has been localized to distributed cortical regions that represent specific attributes. A challenging question is how object semantic space is formed. We tested a novel framework of representing semantic space in the pattern of white matter (WM) connections by extending the representational similarity analysis (RSA) to structural lesion pattern and behavioral data in 80 brain-damaged patients. For each WM connection, a neural representational dissimilarity matrix (RDM) was computed by first building machine-learning models with the voxel-wise WM lesion patterns as features to predict naming performance of a particular item and then computing the correlation between the predicted naming score and the actual naming score of another item in the testing patients. This correlation was used to build the neural RDM based on the assumption that if the connection pattern contains certain aspects of information shared by the naming processes of these two items, models trained with one item should also predict naming accuracy of the other. Correlating the neural RDM with various cognitive RDMs revealed that neural patterns in several WM connections that connect left occipital/middle temporal regions and anterior temporal regions associated with the object semantic space. Such associations were not attributable to modality-specific attributes (shape, manipulation, color, and motion), to peripheral picture-naming processes (picture visual similarity, phonological similarity), to broad semantic categories, or to the properties of the cortical regions that they connected, which tended to represent multiple modality-specific attributes. That is, the semantic space could be represented through WM connection patterns across cortical regions representing modality-specific attributes.

One of the most challenging questions in cognitive neuroscience is how semantic knowledge, for example, that “scissors” and “knives” are related in meaning, can emerge from primary sensory dimensions such as visual forms. It is often assumed that in the human brain, semantics are stored in regions of the brain cortex, where distinct types of modality-specific information are transferred to and bind together. We tested an alternative hypothesis—“representation by connection”—in which higher-order semantic information could be coded by means of connection patterns between cortical regions. Combining data from behavior and brain imaging of 80 patients with brain lesions, we applied machine learning to construct the mapping models between the lesion patterns on axonal tracts (white matter) and item-specific object-naming performances. We found that specific white matter lesions produced deficits in object naming associated with the object’s semantic space, but not relevant to its primary dimension. The naming performances of semantically related objects were better predicted from white matter lesion-pattern models. That is, the higher-order semantic space could be coded in patterns of brain connections by linking cortical areas that do not necessarily contain such information.

The Roles of Left Versus Right Anterior Temporal Lobes in Semantic Memory: A Neuropsychological Comparison of Postsurgical Temporal Lobe Epilepsy Patients

The presence and degree of specialization between the anterior temporal lobes (ATLs) is a key issue in debates about the neural architecture of semantic memory. Here, we comprehensively assessed multiple aspects of semantic cognition in a large group of postsurgical temporal lobe epilepsy (TLE) patients with left versus right anterior temporal lobectomy (n = 40). Both subgroups showed deficits in expressive and receptive verbal semantic tasks, word and object recognition, naming and recognition of famous faces and perception of faces and emotions. Graded differences in performance between the left and right groups were secondary to the overall mild semantic impairment; primarily, left resected TLE patients showed weaker performance on tasks that required naming or accessing semantic information from a written word. Right resected TLE patients were relatively more impaired at recognizing famous faces as familiar, although this effect was observed less consistently. These findings unify previous partial, inconsistent results and also align directly with fMRI and transcranial magnetic stimulation results in neurologically intact participants. Taken together, these data support a model in which the 2 ATLs act as a coupled bilateral system for the representation of semantic knowledge, and in which graded hemispheric specializations emerge as a consequence of differential connectivity to lateralized speech production and face perception regions.

From percept to concept in the ventral temporal lobes: Graded hemispheric specialisation based on stimulus and task

The left and right ventral anterior temporal lobes (vATL) have been implicated as key regions for the representation of conceptual knowledge. However, the nature and degree of hemispheric specialisation in their function is unclear. To address this issue, we investigated hemispheric specialisation in the ventral temporal lobes using a distortion-corrected spin-echo fMRI protocol that enhanced signal in vATL. We employed an orthogonal manipulation of stimulus (written words vs pictured objects) and task (naming vs recognition). Words elicited left-lateralised vATL activation while objects elicited bilateral activation with no hemispheric bias. In contrast, posterior ventral temporal cortex exhibited a rightward bias for objects as well as a leftward bias for words. Naming tasks produced left-lateralised activation in vATL while activity for recognition was equal in left and right vATLs. These findings are incompatible with proposals that left and right ATLs are strongly modular in function, since these predict rightward as well as leftward biases. Instead, they support an alternative model in which (a) left and right ATL together form a bilateral, integrated system for the representation of concepts and (b) within this system, graded hemispheric specialisation emerges as a consequence of differential connectivity with other neural systems. On this view, greater left vATL activation for written word processing develops as a consequence of the inputs this region receives from left-lateralised visual word processing system in posterior temporal cortex. Greater left vATL activation during naming tasks is most likely due to connectivity with left-lateralised speech output systems in prefrontal and motor cortices.