Activation of multi-modal cortical areas underlies short-term memory

Relationship between Motor Competence, Physical Fitness, and Academic Achievement in Young School-Aged Children

Children in schools are facing many academic challenges. Moreover, there is constant pressure on children and parents to maximize academic achievement. We aimed to determine the relationship between motor competence, physical fitness, and academic achievement in young school-aged children. Participants were 130 elementary school children (mean ± SD8.60 ± 0.61 years; 51 boys and 79 girls) from Serbia. The KTK (Körperkoordinations Test für Kinder) battery of tests was used to assess the motor competence in children; children' physical fitness was assessed using the EUROFIT battery of tests, while academic achievement was assessed based on the children's GPA (grade point average) scores at the end of the school year. Pearson's r showed the weak to moderate relationships between the GPA and motor competence and physical fitness measures. The GPA correlates positively and significantly with almost all motor competence and physical fitness measures, but negatively with BMI (p ≤ 0.05). However, the hierarchical linear regression indicated only the plate tapping and sit and reach as the significant predictors of the GPA. Although both tests positively affect the GPA, the plate tapping (B = -0.22, p = 0.02) tends to influence the GPA more than the sit and reach test (B = 0.18, p = 0.04) after adjusting for effects of motor competence (B = 0.19, p = 0.03), age (B = -0.01, p = 0.89), and BMI (B = -0.19, p = 0.03). This study provides evidence demonstrating that academic achievement is generally associated with physical fitness and motor competence in children. However, plate taping and sit and reach were accounted as the most important predictors for academic achievement.

Effects of Transcranial Direct Current Stimulation Paired With Cognitive Training on Functional Connectivity of the Working Memory Network in Older Adults

Background

Working memory, a fundamental short-term cognitive process, is known to decline with advanced age even in healthy older adults. Normal age-related declines in working memory can cause loss of independence and decreased quality of life. Cognitive training has shown some potential at enhancing certain cognitive processes, although, enhancements are variable. Transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, has shown promise at enhancing working memory abilities, and may further the benefits from cognitive training interventions. However, the neural mechanisms underlying tDCS brain-based enhancements remain unknown.

Objective/Hypothesis

Assess the effects of a 2-week intervention of active-tDCS vs. sham paired with cognitive training on functional connectivity of the working memory network during an N-Back working memory task.

Methods

Healthy older adults (N = 28; mean age = 74 ± 7.3) completed 10-sessions of cognitive training paired with active or sham-tDCS. Functional connectivity was evaluated at baseline and post-intervention during an N-Back task (2-Back vs. 0-Back).

Results

Active-tDCS vs. sham demonstrated a significant increase in connectivity between the left dorsolateral prefrontal cortex and right inferior parietal lobule at post-intervention during 2-Back. Target accuracy on 2-Back was significantly improved for active vs. sham at post-intervention.

Conclusion

These results suggest pairing tDCS with cognitive training enhances functional connectivity and working memory performance in older adults, and thus may hold promise as a method for remediating age-related cognitive decline. Future studies evaluating optimal dose and long-term effects of tDCS on brain function will help to maximize potential clinical impacts of tDCS paired with cognitive training in older adults.

Clinical Trial Registration:

www.ClinicalTrials.gov, identifier NCT02137122.

The Causal Role of the Prefrontal Cortex and Somatosensory Cortex in Tactile Working Memory

In the present study, we searched for causal evidence linking activity in the bilateral primary somatosensory cortex (SI), posterior parietal cortex (PPC), and prefrontal cortex (PFC) with behavioral performance in vibrotactile working memory. Participants performed a vibrotactile delayed matching-to-sample task, while single-pulse transcranial magnetic stimulation (sp-TMS) was applied over these cortical areas at 100, 200, 300, 600, 1600, and 1900 ms after the onset of vibrotactile stimulation (200 ms duration). In our experiments, sp-TMS over the contralateral SI at the early delay (100 and 200 ms) deteriorated the accuracy of task performance, and over the ipsilateral SI at the late delay (1600 and 1900 ms) also induced such deteriorating effects. Furthermore, deteriorating effects caused by sp-TMS over the contralateral DLPFC at the same maintenance stage (1600 ms) were correlated with the effects caused by sp-TMS over the ipsilateral SI, indicating that information retained in the ipsilateral SI during the late delay may be associated with the DLPFC. Taken together, these results suggest that both the contralateral and ipsilateral SIs are involved in tactile WM, and the contralateral DLPFC bridges the contralateral SI and ipsilateral SI for goal-directed action.

SPARCL1 Accelerates Symptom Onset in Alzheimer's Disease and Influences Brain Structure and Function During Aging

We recently reported that alpha-2 macroglobulin (A2M) is a biomarker of neuronal injury in Alzheimer's disease (AD) and identified a network of nine genes co-expressed with A2M in the brain. This network includes the gene encoding SPARCL1, a protein implicated in synaptic maintenance. Here, we examine whether SPARCL1 is associated with longitudinal changes in brain structure and function in older individuals at risk for AD in the Baltimore Longitudinal Study of Aging. Using data from the Gene-Tissue Expression Project, we first identified two single nucleotide polymorphisms (SNPs), rs9998212 and rs7695558, associated with lower brain SPARCL1 gene expression. We then analyzed longitudinal trajectories of cognitive performance in 591 participants who remained cognitively normal (average follow-up interval: 11.8 years) and 129 subjects who eventually developed MCI or AD (average follow-up interval: 9.4 years). Cognitively normal minor allele carriers of rs7695558 who developed incident AD showed accelerated memory loss prior to disease onset. Next, we compared longitudinal changes in brain volumes (MRI; n = 120 participants; follow-up = 6.4 years; 826 scans) and resting-state cerebral blood flow (rCBF; 15O-water PET; n = 81 participants; follow-up = 7.7 years; 664 scans) in cognitively normal participants. Cognitively normal minor allele carriers of rs9998212 showed accelerated atrophy in several global, lobar, and regional brain volumes. Minor allele carriers of both SNPs showed longitudinal changes in rCBF in several brain regions, including those vulnerable to AD pathology. Our findings suggest that SPARCL1 accelerates AD pathogenesis and thus link neuroinflammation with widespread changes in brain structure and function during aging.

Brain processing of the temporal dimension of acute pain in short-term memory

The dynamics of noxious sensation shapes pain perception, yet the memory of the temporal dimension of pain remains almost completely unexplored. Here, brain activity during the memory of pain duration was contrasted with that associated with the memory of pain intensity using functional magnetic resonance imaging and a delayed reproduction task. Participants encoded, maintained during a short delay, and reproduced (1) the "duration" of pain (ie, onset-to-offset), (2) the "dynamics" of pain (ie, evolution of pain over time), or (3) the intensity of pain (ie, control with no explicit temporal processing required). Results show that the inferior frontal gyrus/insula and adjacent striatal structures as well as the supramarginal and middle temporal gyri are activated in the duration task compared to the control intensity task. Specific examination of the memory delay of the duration task further revealed activation in the supramarginal gyrus extending to the parietal operculum (possibly SII) and primary somatosensory cortex (SI). In contrast, the memory delay of the dynamic task involved the bilateral supplementary motor area and the frontoparietal attentional network. Although SI, SII, and insula may contribute to the memory trace of pain sensation, other areas less commonly reported in pain studies are associated with time processing and may therefore contribute to the processing of temporal aspects of pain. Results further suggest a differential role of core timing regions of the brain depending on specific task instructions and attentional allocations to the single dimension of time, as compared to the joint processing of both time and intensity.

Blood metabolite markers of cognitive performance and brain function in aging

We recently showed that Alzheimer's disease patients have lower plasma concentrations of the phosphatidylcholines (PC16:0/20:5; PC16:0/22:6; and PC18:0/22:6) relative to healthy controls. We now extend these findings by examining associations between plasma concentrations of these PCs with cognition and brain function (measured by regional resting state cerebral blood flow; rCBF) in non-demented older individuals. Within the Baltimore Longitudinal Study of Aging neuroimaging substudy, participants underwent cognitive assessments and brain (15)O-water positron emission tomography. Plasma phosphatidylcholines concentrations (PC16:0/20:5, PC16:0/22:6, and PC18:0/22:6), cognition (California Verbal Learning Test (CVLT), Trail Making Test A&B, the Mini-Mental State Examination, Benton Visual Retention, Card Rotation, and Fluencies-Category and Letter), and rCBF were assessed. Lower plasma phosphatidylcholine concentrations were associated with lower baseline memory performance (CVLT long delay recall task-PC16:0/20:5: -2.17-1.39-0.60 p = 0.001 (β with 95% confidence interval subscripts)) and lower rCBF in several brain regions including those associated with memory performance and higher order cognitive processes. Our findings suggest that lower plasma concentrations of PC16:0/20:5, PC16:0/22:6, and PC18:0/22:6 are associated with poorer memory performance as well as widespread decreases in brain function during aging. Dysregulation of peripheral phosphatidylcholine metabolism may therefore be a common feature of both Alzheimer's disease and age-associated differences in cognition.

The neuroscience of working memory capacity and training

Working memory - the ability to maintain and manipulate information over a period of seconds - is a core component of higher cognitive functions. The storage capacity of working memory is limited but can be expanded by training, and evidence of the neural mechanisms underlying this effect is accumulating. Human imaging studies and neurophysiological recordings in non-human primates, together with computational modelling studies, reveal that training increases the activity of prefrontal neurons and the strength of connectivity in the prefrontal cortex and between the prefrontal and parietal cortex. Dopaminergic transmission could have a facilitatory role. These changes more generally inform us of the plasticity of higher cognitive functions.

Cooperative processing in primary somatosensory cortex and posterior parietal cortex during tactile working memory

In the present study, causal roles of both the primary somatosensory cortex (SI) and the posterior parietal cortex (PPC) were investigated in a tactile unimodal working memory (WM) task. Individual magnetic resonance imaging-based single-pulse transcranial magnetic stimulation (spTMS) was applied, respectively, to the left SI (ipsilateral to tactile stimuli), right SI (contralateral to tactile stimuli) and right PPC (contralateral to tactile stimuli), while human participants were performing a tactile-tactile unimodal delayed matching-to-sample task. The time points of spTMS were 300, 600 and 900 ms after the onset of the tactile sample stimulus (duration: 200 ms). Compared with ipsilateral SI, application of spTMS over either contralateral SI or contralateral PPC at those time points significantly impaired the accuracy of task performance. Meanwhile, the deterioration in accuracy did not vary with the stimulating time points. Together, these results indicate that the tactile information is processed cooperatively by SI and PPC in the same hemisphere, starting from the early delay of the tactile unimodal WM task. This pattern of processing of tactile information is different from the pattern in tactile-visual cross-modal WM. In a tactile-visual cross-modal WM task, SI and PPC contribute to the processing sequentially, suggesting a process of sensory information transfer during the early delay between modalities.

NIH Toolbox Cognition Battery (NIHTB-CB): list sorting test to measure working memory

The List Sorting Working Memory Test was designed to assess working memory (WM) as part of the NIH Toolbox Cognition Battery. List Sorting is a sequencing task requiring children and adults to sort and sequence stimuli that are presented visually and auditorily. Validation data are presented for 268 participants ages 20 to 85 years. A subset of participants (N=89) was retested 7 to 21 days later. As expected, the List Sorting Test had moderately high correlations with other measures of working memory and executive functioning (convergent validity) but a low correlation with a test of receptive vocabulary (discriminant validity). Furthermore, List Sorting demonstrates expected changes over the age span and has excellent test-retest reliability. Collectively, these results provide initial support for the construct validity of the List Sorting Working Memory Measure as a measure of working memory. However, the relationship between the List Sorting Test and general executive function has yet to be determined.

Associations between gross motor coordination and academic achievement in elementary school children

We aimed to evaluate the relationship between gross motor coordination (MC) and academic achievement (AA) in a sample of Portuguese children aged 9-12 years. The study took place during the 2009/2010 school year and involved 596 urban children (281 girls) from the north of Portugal. AA was assessed using the Portuguese Language and Mathematics National Exams. Gross MC was evaluated with the Körperkoordination Test für Kinder. Cardiorespiratory fitness was predicted by a maximal multistage 20-m shuttle-run test of the Fitnessgram Test Battery. Body weight and height were measured following standard procedures. Socio-economic status was based on annual family income. Logistic Regression was used to analyze the association of gross MC with AA. 51.6% of the sample exhibited MC disorders or MC insufficiency and none of the participants showed very good MC. In both genders, children with insufficient MC or MC disorders exhibited a higher probability of having low AA, compared with those with normal or good MC (p<.05 for trend for both) after adjusting for cardiorespiratory fitness, body mass index and socio-economic status.

The neural substrate for working memory of tactile surface texture

Fine surface texture is best discriminated by touch, in contrast to macro geometric features like shape. We used functional magnetic resonance imaging and a delayed match-to-sample task to investigate the neural substrate for working memory of tactile surface texture. Blindfolded right-handed males encoded the texture or location of up to four sandpaper stimuli using the dominant or non-dominant hand. They maintained the information for 10-12 s and then answered whether a probe stimulus matched the memory array. Analyses of variance with the factors Hand, Task, and Load were performed on the estimated percent signal change for the encoding and delay phase. During encoding, contralateral effects of Hand were found in sensorimotor regions, whereas Load effects were observed in bilateral postcentral sulcus (BA2), secondary somatosensory cortex (S2), pre-SMA, dorsolateral prefrontal cortex (dlPFC), and superior parietal lobule (SPL). During encoding and delay, Task effects (texture > location) were found in central sulcus, S2, pre-SMA, dlPFC, and SPL. The Task and Load effects found in hand- and modality-specific regions BA2 and S2 indicate involvement of these regions in the tactile encoding and maintenance of fine surface textures. Similar effects in hand- and modality-unspecific areas dlPFC, pre-SMA and SPL suggest that these regions contribute to the cognitive monitoring required to encode and maintain multiple items. Our findings stress both the particular importance of S2 for the encoding and maintenance of tactile surface texture, as well as the supramodal nature of parieto-frontal networks involved in cognitive control.

The role of the cerebellum in schizophrenia: from cognition to molecular pathways

Beside its role in motor coordination, the cerebellum is involved in cognitive function such as attention, working memory, verbal learning, and sensory discrimination. In schizophrenia, a disturbed prefronto-thalamo-cerebellar circuit has been proposed to play a role in the pathophysiology. In addition, a deficit in the glutamatergic N-methyl-D-aspartate (NMDAf) receptor has been hypothesized. The risk gene neuregulin 1 may play a major role in this process. We demonstrated a higher expression of the NMDA receptor subunit 2D in the right cerebellar regions of schizophrenia patients, which may be a secondary upregulation due to a dysfunctional receptor. In contrast, the neuregulin 1 risk variant containing at least one C-allele was associated with decreased expression of NMDA receptor subunit 2C, leading to a dysfunction of the NMDA receptor, which in turn may lead to a dysfunction of the gamma amino butyric acid (GABA) system. Accordingly, from post-mortem studies, there is accumulating evidence that GABAergic signaling is decreased in the cerebellum of schizophrenia patients. As patients in these studies are treated with antipsychotics long term, we evaluated the effect of long-term haloperidol and clozapine treatment in an animal model. We showed that clozapine may be superior to haloperidol in restoring a deficit in NMDA receptor subunit 2C expression in the cerebellum. We discuss the molecular findings in the light of the role of the cerebellum in attention and cognitive deficits in schizophrenia.

Training and plasticity of working memory

Working memory (WM) capacity predicts performance in a wide range of cognitive tasks. Although WM capacity has been viewed as a constant trait, recent studies suggest that it can be improved by adaptive and extended training. This training is associated with changes in brain activity in frontal and parietal cortex and basal ganglia, as well as changes in dopamine receptor density. Transfer of the training effects to non-trained WM tasks is consistent with the notion of training-induced plasticity in a common neural network for WM. The observed training effects suggest that WM training could be used as a remediating intervention for individuals for whom low WM capacity is a limiting factor for academic performance or in everyday life.

Intracranial electroencephalography reveals two distinct similarity effects during item recognition

Behavioral studies of visual recognition memory indicate that old/new decisions reflect both the similarity of the probe to the studied items (probe-item similarity) and the similarities among the studied items themselves (list homogeneity). Recording intracranial electroencephalography from 1,155 electrodes across 15 patients, we examined the oscillatory correlates of probe-item similarity and homogeneity effects in short-term recognition memory for synthetic faces. Frontal areas show increases in low-frequency oscillations with both probe-item and item-item similarity, whereas temporal lobe areas show distinct oscillatory correlates for probe-item similarity and homogeneity in the gamma band. We discuss these frontal low-frequency effects and the dissociation in the temporal lobe in terms of recent computational models of visual recognition memory.

Common and unique components of inhibition and working memory: an fMRI, within-subjects investigation

Behavioural findings indicate that the core executive functions of inhibition and working memory are closely linked, and neuroimaging studies indicate overlap between their neural correlates. There has not, however, been a comprehensive study, including several inhibition tasks and several working memory tasks, performed by the same subjects. In the present study, 11 healthy adult subjects completed separate blocks of 3 inhibition tasks (a stop task, a go/no-go task and a flanker task), and 2 working memory tasks (one spatial and one verbal). Activation common to all 5 tasks was identified in the right inferior frontal gyrus, and, at a lower threshold, also the right middle frontal gyrus and right parietal regions (BA 40 and BA 7). Left inferior frontal regions of interest (ROIs) showed a significant conjunction between all tasks except the flanker task. The present study could not pinpoint the specific function of each common region, but the parietal region identified here has previously been consistently related to working memory storage and the right inferior frontal gyrus has been associated with inhibition in both lesion and imaging studies. These results support the notion that inhibitory and working memory tasks involve common neural components, which may provide a neural basis for the interrelationship between the two systems.

Mapping cognitive function

Cognitive functions are fundamental to being human. Although tremendous progress has been made in the science of cognition using neuroimaging, the clinical applications of neuroimaging are just beginning to be realized. This article focuses on selected technologies, analysis techniques, and applications that have, or will soon have, direct clinical impact. The authors discuss how cognition can be imaged using MR imaging, functional MR imaging, positron emission tomography, magnetoencephalography and electroencephalography, and MR imaging diffusion tensor imaging. A unifying theme of this article is the concept that a more complete understanding of cognition only comes through integration of multimodal structural and functional imaging technologies.

Unity and diversity of tonic and phasic executive control components in episodic and working memory

The present study aimed to delineate the extent to which unitary executive functions might be shared across the separate domains of episodic and working memory. A mixed blocked/event-related functional magnetic resonance imaging (fMRI) design was employed to assess sustained (tonic control) and transient (phasic control) brain responses arising from incrementing executive demand (source versus item episodic memory - vis-à-vis - two-back versus one-back working memory) using load-dependent activation overlaps as indices of common components. Although an extensive portion of the regional load effects constituted differential control modulations in both sustained and transient responses, commonalities were also found implicating a subset of executive core mechanisms consistent with unitary or domain general control. 'Unitary' control modulations were temporally dissociated into (1) shared tonic components involving medial and lateral prefrontal cortex, striatum, cerebellum and superior parietal cortex, assumed to govern enhanced top-down context processing, monitoring and sustained attention throughout task periods and (2) stimulus-synchronous phasic components encompassing posterior intraparietal sulcus, hypothesized to support dynamic shifting of the 'focus of attention' among internal representations. Taken together, these results converge with theoretical models advocating both unity and diversity among executive control processes.

Syntax production in bilinguals

We used fMRI to examine the functional correlates of syntactical processing in the first (L1) and second (L2) languages of non-proficient, late bilinguals. Subjects either covertly read words or produced sentences from them. Syntactical production during sentence production activated regions including left inferior frontal (LIFG) gyrus and the supplementary motor area in both languages. Analyses performed on the LIFG activation identified on a subject-by-subject basis revealed greater activation in L2 compared to L1 during sentence production and during word reading, consistent with previous work suggesting that greater cognitive effort may be subserved by less well-tuned neural representations that require greater neuronal activity. Remarkably, there was a greater separation in the LIFG activations in L1 versus L2 in less compared to more proficient bilinguals during syntax production, suggesting a functional reorganisation of regions involved in syntactical production as a function of syntactical proficiency.

Biasing the brain's attentional set: I. cue driven deployments of intersensory selective attention

Brain activity associated with directing attention to one of two possible sensory modalities was examined using high-density mapping of human event-related potentials. The deployment of selective attention was based on visually presented symbolic cue-words instructing subjects on a trial-by-trial basis, which sensory modality to attend. We measured the spatio-temporal pattern of activation in the approximately 1 second period between the cue-instruction and a subsequent compound auditory-visual imperative stimulus. This allowed us to assess the flow of processing across brain regions involved in deploying and sustaining inter-sensory selective attention, prior to the actual selective processing of the compound audio-visual target stimulus. Activity over frontal and parietal areas showed sensory specific increases in activation during the early part of the anticipatory period (~230 ms), probably representing the activation of fronto-parietal attentional deployment systems for top-down control of attention. In the later period preceding the arrival of the "to-be-attended" stimulus, sustained differential activity was seen over fronto-central regions and parieto-occipital regions, suggesting the maintenance of sensory-specific biased attentional states that would allow for subsequent selective processing. Although there was clear sensory biasing in this late sustained period, it was also clear that both sensory systems were being prepared during the cue-target period. These late sensory-specific biasing effects were also accompanied by sustained activations over frontal cortices that also showed both common and sensory specific activation patterns, suggesting that maintenance of the biased state includes top-down inputs from generators in frontal cortices, some of which are sensory-specific regions. These data support extensive interactions between sensory, parietal and frontal regions during processing of cue information, deployment of attention, and maintenance of the focus of attention in anticipation of impending attentionally relevant input.

Working memory in primate sensory systems

Sensory working memory consists of the short-term storage of sensory stimuli to guide behaviour. There is increasing evidence that elemental sensory dimensions - such as object motion in the visual system or the frequency of a sound in the auditory system - are stored by segregated feature-selective systems that include not only the prefrontal and parietal cortex, but also areas of sensory cortex that carry out relatively early stages of processing. These circuits seem to have a dual function: precise sensory encoding and short-term storage of this information. New results provide insights into how activity in these circuits represents the remembered sensory stimuli.

A relationship between cerebellar Purkinje cells and spatial working memory demonstrated in a lurcher/chimera mouse model system

New emphasis has been placed upon cerebellar research because of recent reports demonstrating involvement of the cerebellum in non-motor cognitive behaviors. Included in the growing list of cognitive functions associated with cerebellar activation is working memory. In this study, we explore the potential role of the cerebellum in spatial working memory using a mouse model of Purkinje cell loss. Specifically, we make aggregation chimeras between heterozygous lurcher (Lc/+) mutant embryos and +/+ (wildtype) embryos and tested them in the delayed matching-to-position (DMTP) task. Lc/+ mice lose 100% of their Purkinje cells postnatally due to a cell-intrinsic gain-of-function mutation. Lc/+<->+/+ chimeras therefore have Purkinje cells ranging from 0 to normal numbers. Through histological examination of chimeric mice and observations of motor ability, we showed that ataxia is dependent upon both the number and distribution of Purkinje cells in the cerebellum. In addition, we found that Lc/+ mice, with a complete loss of Purkinje cells, have a generalized deficit in DMTP performance that is probably associated with their motor impairment. Finally, we found that Lc/+<->+/+ chimeric mice, as a group, did not differ from control mice in this task. Rather, surprisingly, analysis of their total Purkinje cells and performance in the DMTP task revealed a significant negative relationship between these two variables. Together, these findings indicate that the cerebellum plays a minor or indirect role in spatial working memory.

Modality effects in verbal working memory: differential prefrontal and parietal responses to auditory and visual stimuli

The neural bases of verbal (nonspatial) working memory (VWM) have been primarily examined using visual stimuli. Few studies have investigated the neural bases of VWM using auditory stimuli, and fewer have explored modality differences in VWM. In this study, we used functional magnetic resonance imaging (fMRI) to examine similarities and differences between visual VWM (vis-VWM) and auditory VWM (aud-VWM) utilizing identical stimuli and a within-subjects design. Performance levels were similar in the two modalities and there was extensive overlap of activation bilaterally in the dorsolateral and ventrolateral prefrontal cortex (DLPFC and VLPFC), intraparietal sulcus, supramarginal gyrus and the basal ganglia. However, a direct statistical comparison revealed significant modality differences: the left posterior parietal cortex, primarily along the intraparietal sulcus, showed greater responses during vis-VWM whereas the left dorsolateral prefrontal cortex showed greater responses during aud-VWM. No such differences were observed in the right hemisphere. Other modality differences in VWM were also observed, but they were associated with relative decreases in activation. In particular, we detected bilateral suppression of the superior and middle temporal (auditory) cortex during vis-VWM, and of the occipital (visual) cortex during aud-VWM, thus suggesting that cross-modal inhibitory processes may help to provide preferential access to high-order heteromodal association areas. Taken together, our findings suggest that although similar prefrontal and parietal regions are involved in aud-VWM and vis-VWM, there are important modality differences in the way neural signals are generated, processed and routed during VWM.

Direction of cross-modal information transfer affects human brain activation: a PET study

The purpose of this study was to determine the functional organization of the human brain involved in cross-modal discrimination between tactile and visual information. Regional cerebral blood flow was measured by positron emission tomography in nine right-handed volunteers during four discrimination tasks; tactile-tactile (TT), tactile-visual (TV), visual-tactile (VT), and visual-visual (VV). The subjects were asked either to look at digital cylinders of different diameters or to grasp the digital cylinders with the thumb and index finger of the right hand using haptic interfaces. Compared with the motor control task in which the subjects looked at and grasped cylinders of the same diameter, the right lateral prefrontal cortex and the right inferior parietal lobule were activated in all the four discrimination tasks. In addition, the dorsal premotor cortex, the ventral premotor cortex, and the inferior temporal cortex of the right hemisphere were activated during VT but not during TV. Our results suggest that the human brain mechanisms underlying cross-modal discrimination have two different pathways depending on the temporal order in which stimuli are presented.

Increased brain activity in frontal and parietal cortex underlies the development of visuospatial working memory capacity during childhood

The aim of this study was to identify changes in brain activity associated with the increase in working memory (WM) capacity that occurs during childhood and early adulthood. Functional MRI (fMRI) was used to measure brain activity in subjects between 9 and 18 years of age while they performed a visuospatial WM task and a baseline task. During performance of the WM task, the older children showed higher activation of cortex in the superior frontal and intraparietal cortex than the younger children did. A second analysis found that WM capacity was significantly correlated with brain activity in the same regions. These frontal and parietal areas are known to be involved in the control of attention and spatial WM. The development of the functionality in these areas may play an important role in cognitive development during childhood.

Parametrically dissociating speech and nonspeech perception in the brain using fMRI

Candidate brain regions constituting a neural network for preattentive phonetic perception were identified with fMRI and multivariate multiple regression of imaging data. Stimuli contrasted along speech/nonspeech, acoustic, or phonetic complexity (three levels each) and natural/synthetic dimensions. Seven distributed brain regions' activity correlated with speech and speech complexity dimensions, including five left-sided foci [posterior superior temporal gyrus (STG), angular gyrus, ventral occipitotemporal cortex, inferior/posterior supramarginal gyrus, and middle frontal gyrus (MFG)] and two right-sided foci (posterior STG and anterior insula). Only the left MFG discriminated natural and synthetic speech. The data also supported a parallel rather than serial model of auditory speech and nonspeech perception.

Evidence for the involvement of the ventro-medial prefrontal cortex in a short-term storage of visual images

The purpose of this study was to clarify the role of the ventro-medial prefrontal cortex in short-term visual memory. Patients with focal lesions to the right gyrus rectus were impaired on a size judgement task, which required short-term retention of laterally presented visual patterns. The impairment was most evident when the stimuli were addressed to the damaged hemisphere (left visual field presentations) and when separated by very short (50-500 ms) intervals. The findings suggest that the ventro-medial part of the orbitofrontal cortex, like the ventro-lateral part, is involved in short-term storage of icon-like representations of visual objects, and also that there exists a right-hemispheric specialization for that function. Our study presents the first direct evidence of such specific memory effects in humans using a lesion method and points to the importance of the right gyrus rectus area in maintaining the representation of stimuli after they are removed from view.

Domain-specific distribution of working memory processes along human prefrontal and parietal cortices: a functional magnetic resonance imaging study

This study reinvestigated the functional neuroanatomy of phonological and visual working memory in humans. Articulatory suppression was used to deprive the human subjects of species-specific verbal strategies in order to make the functional magnetic resonance imaging results more comparable to findings in non-human primates. Both phonological and visual working memory processes activated similar prefronto-parietal networks but were found to be differentially distributed along several cortical structures, in particular along the anterior and posterior parts of the intermediate frontal sulcus. These results suggest that a domain-specific topographical organization of neural working memory mechanisms in the primate brain is conserved in evolution. However, the findings also underline the critical dynamic influence that the additional availability of language may have on working memory processes and their functional implementation in the human brain.

Attending to and remembering tactile stimuli: a review of brain imaging data and single-neuron responses

Clinical and neuroimaging observations of the cortical network implicated in tactile attention have identified foci in parietal somatosensory, posterior parietal, and superior frontal locations. Tasks involving intentional hand-arm movements activate similar or nearby parietal and frontal foci. Visual spatial attention tasks and deliberate visuomotor behavior also activate overlapping posterior parietal and frontal foci. Studies in the visual and somatosensory systems thus support a proposal that attention to the spatial location of an object engages cortical regions responsible for the same coordinate referents used for guiding purposeful motor behavior. Tactile attention also biases processing in the somatosensory cortex through amplification of responses to relevant features of selected stimuli. Psychophysical studies demonstrate retention gradients for tactile stimuli like those reported for visual and auditory stimuli, and suggest analogous neural mechanisms for working memory across modalities. Neuroimaging studies in humans using memory tasks, and anatomic studies in monkeys support the idea that tactile information relayed from the somatosensory cortex is directed ventrally through the insula to the frontal cortex for short-term retention and to structures of the medial temporal lobe for long-term encoding. At the level of single neurons, tactile (such as visual and auditory) short-term memory appears as a persistent response during delay intervals between sampled stimuli.

Single-photon emission computed tomography of the brain in autism: effect of the developmental level

Brain single-photon emission computed tomography was performed in 22 autistic and 10 nonautistic disabled patients. The regional cerebral blood flow in both laterotemporal and dorso-medio-lateral frontal areas decreased significantly in the autistic group compared with in nonautistic group. In the autistic group, the regional cerebral blood flow was significantly higher in the right temporal and right parietal lobes than that in the left ones. Inversely, the regional cerebral blood flow in the frontal and occipital lobes was significantly higher on the left side than on the right side. In the nonautistic group, except for in the dorso-medio-lateral frontal lobes (left > right), there was no difference in the regional cerebral blood flow in either cerebrum or cerebellum. A positive correlationship between regional cerebral flow and development quotient (intelligence quotient) was observed in the left laterotemporal and both dorso-medio-lateral frontal areas, and a negative one was observed in the cerebellar vermis area. These results suggest that the regional cerebral blood flow decrease in the temporal and frontal areas relates to not only the brain mechanism of autism reported previously but also intelligence levels.

Patterns of regional brain activation associated with different forms of motor learning

To examine the variations in regional cerebral blood flow during execution and learning of reaching movements, we employed a family of kinematically and dynamically controlled motor tasks in which cognitive, mnemonic and executive features of performance were differentiated and characterized quantitatively. During 15O-labeled water positron emission tomography (PET) scans, twelve right-handed subjects moved their dominant hand on a digitizing tablet from a central location to equidistant targets displayed with a cursor on a computer screen in synchrony with a tone. In the preceding week, all subjects practiced three motor tasks: 1) movements to a predictable sequence of targets; 2) learning of new visuomotor transformations in which screen cursor motion was rotated by 30 degrees -60 degrees; 3) learning new target sequences by trial and error, by using previously acquired routines in a task placing heavy load on spatial working memory. The control condition was observing screen and audio displays. Subtraction images were analyzed with Statistical Parametric Mapping to identify significant brain activation foci. Execution of predictable sequences was characterized by a modest decrease in movement time and spatial error. The underlying pattern of activation involved primary motor and sensory areas, cerebellum, basal ganglia. Adaptation to a rotated reference frame, a form of procedural learning, was associated with decrease in the imposed directional bias. This task was associated with activation in the right posterior parietal cortex. New sequences were learned explicitly. Significant activation was found in dorsolateral prefrontal and anterior cingulate cortices. In this study, we have introduced a series of flexible motor tasks with similar kinematic characteristics and different spatial attributes. These tasks can be used to assess specific aspects of motor learning with imaging in health and disease.

Human oscillatory brain activity within gamma band (30-50 Hz) induced by visual recognition of non-stable postures

Our principal finding from this study is that there were changes at the level of brain electrical activity (EEG) during cognitive tasks while subjects were instructed to visually recognize non-stable postures of a computer animated human body model. In particular, there was clear enhancement of the amplitude within the gamma band (30-50 Hz) activity associated with visual recognition of non-stable postures at fronto-central and parietal areas in all subjects. The Morlet's wavelet transform was applied to examine the change of time-frequency (TF) energy within a range of 1-70 Hz frequencies range as a function of experimental tasks. There was a high energy burst within the 35-45 Hz TF cluster at fronto-central and parietal areas when subjects visually recognized non-stable postures. Experimental evidences were provided demonstrating that EEG activity recorded during visual recognition of non-stable postures was related to specific judgement of postural instability. In a series of control experiments, additional evidences were provided to justify the specific sensitivity of EEG 40-Hz activity to the act of visual recognition of postural instability. The contamination of muscle activity in the reported EEG results during perceptual tasks was also ruled out. Our findings are consistent with the notion of existence of specialized neural detectors (predictors) for specific postures and goal-oriented behavior. However, the functional significance and precise cognitive and neurophysiological mechanisms predicting the existence of these detectors remain to be explored.

Cortical activity in precision- versus power-grip tasks: an fMRI study

Most manual grips can be divided in precision and power grips on the basis of phylogenetic and functional considerations. We used functional magnetic resonance imaging to compare human brain activity during force production by the right hand when subjects used a precision grip and a power grip. During the precision-grip task, subjects applied fine grip forces between the tips of the index finger and the thumb. During the power-grip task, subjects squeezed a cylindrical object using all digits in a palmar opposition grasp. The activity recorded in the primary sensory and motor cortex contralateral to the operating hand was higher when the power grip was applied than when subjects applied force with a precision grip. In contrast, the activity in the ipsilateral ventral premotor area, the rostral cingulate motor area, and at several locations in the posterior parietal and prefrontal cortices was stronger while making the precision grip than during the power grip. The power grip was associated predominately with contralateral left-sided activity, whereas the precision-grip task involved extensive activations in both hemispheres. Thus our findings indicate that in addition to the primary motor cortex, premotor and parietal areas are important for control of fingertip forces during precision grip. Moreover, the ipsilateral hemisphere appears to be strongly engaged in the control of precision-grip tasks performed with the right hand.

Cortical centres underlying auditory temporal processing in humans: a PET study

We have used positron emission tomography (PET) to test a specific hypothesis of a neural system subserving auditory temporal processing (acoustical stimulus duration discrimination). Maps of the cerebral blood flow distribution during specific stimulations were obtained from five normally-hearing and otherwise healthy subjects. The auditory stimuli consisted of sounds of varying duration and of auditorily presented words in which the duration of the initial phoneme was manipulated. All stimuli alternated with conditions of silence in a subtraction paradigm. The blood flow distribution was mapped with O-15-labelled water. The results demonstrated that stimuli requiring recognizing, memorizing, or attending to specific target sounds during temporal processing generally resulted in significant activation of both frontal lobes and the parietal lobe in the right hemisphere. Based on these results, we hypothesise that a network consisting of anterior and posterior auditory attention and short-term memory sites subserves acoustical stimulus duration perception and analysis (auditory temporal processing).

Positron emission tomography of cortical centers of tinnitus

Tinnitus is associated with a wide variety of disorders in the auditory system. Whether generated peripherally or centrally, tinnitus is believed to be associated with activity in specific cortical regions. The present study tested the hypothesis that these cortical centers subserve the generation, perception and processing of the tinnitus stimulus and that these processes are suppressed by lidocaine and masking. Positron emission tomography was used to map the tinnitus-specific central activity. By subtracting positron emission tomography images of regional cerebral blood flow distribution obtained during suppression of the tinnitus from positron emission tomography images obtained during the habitual tinnitus sensation, we were able to identify brain areas concerned with the cerebral representation of tinnitus. Increased neuronal activity caused by tinnitus occurred predominantly in the right hemisphere with significant foci in the middle frontal and middle temporal gyri, in addition to lateral and mesial posterior sites. The results are consistent with the hypothesis that the sensation of tinnitus is associated with activity in cortical regions functionally linked to subserve attention, emotion and memory. For the first time, the functional anatomy of conditions with and without the habitual tinnitus sensation was obtained and compared in the same subjects.

Sustained activity in the medial wall during working memory delays

We have taken advantage of the temporal resolution afforded by functional magnetic resonance imaging (fMRI) to investigate the role played by medial wall areas in humans during working memory tasks. We demarcated the medial motor areas activated during simple manual movement, namely the supplementary motor area (SMA) and the cingulate motor area (CMA), and those activated during visually guided saccadic eye movements, namely the supplementary eye field (SEF). We determined the location of sustained activity over working memory delays in the medial wall in relation to these functional landmarks during both spatial and face working memory tasks. We identified two distinct areas, namely the pre-SMA and the caudal part of the anterior cingulate cortex (caudal-AC), that showed similar sustained activity during both spatial and face working memory delays. These areas were distinct from and anterior to the SMA, CMA, and SEF. Both the pre-SMA and caudal-AC activation were identified by a contrast between sustained activity during working memory delays as compared with sustained activity during control delays in which subjects were waiting for a cue to make a simple manual motor response. Thus, the present findings suggest that sustained activity during working memory delays in both the pre-SMA and caudal-AC does not reflect simple motor preparation but rather a state of preparedness for selecting a motor response based on the information held on-line.

An MEG study of picture naming

The purpose of this study was to relate a psycholinguistic processing model of picture naming to the dynamics of cortical activation during picture naming. The activation was recorded from eight Dutch subjects with a whole-head neuromagnetometer. The processing model, based on extensive naming latency studies, is a stage model. In preparing a picture"s name, the speaker performs a chain of specific operations. They are, in this order, computing the visual percept, activating an appropriate lexical concept, selecting the target word from the mental lexicon, phonological encoding, phonetic encoding, and initiation of articulation. The time windows for each of these operations are reasonably well known and could be related to the peak activity of dipole sources in the individual magnetic response patterns. The analyses showed a clear progression over these time windows from early occipital activation, via parietal and temporal to frontal activation. The major specific findings were that (1) a region in the left posterior temporal lobe, agreeing with the location of Wernicke"s area, showed prominent activation starting about 200 msec after picture onset and peaking at about 350 msec (i.e., within the stage of phonological encoding), and (2) a consistent activation was found in the right parietal cortex, peaking at about 230 msec after picture onset, thus preceding and partly overlapping with the left temporal response. An interpretation in terms of the management of visual attention is proposed.

Modality-specific subregions in human inferior parietal lobule: a magnetoencephalographic study during cognitive tasks

The inferior parietal lobule (IPL) has been considered to be a multimodal sensory association area. Both event-related potentials and magnetic responses have examined the relationships between IPL and cognitive processing. However, there have been no studies clarifying the functional subregions in IPL. We studied the event-related magnetic response during conventional auditory and visual oddball paradigms. We were able to distinguish non-invasively modality-specific subregions in IPL. The subregion in IPL activated by auditory target stimuli was located more anterior and superior than that responding to visual target stimuli on each hemisphere. The data suggests that modality-specific subregions in the IPL are differentially activated by auditory or visual stimuli.

The role of the left inferior temporal cortex for visual pattern discrimination--a PET study

We measured regional cerebral blood flow using positron emission tomography in seven normal volunteers during discrimination tasks for visual patterns. For the 'attention to right or left' tasks, the subjects were instructed to press a key when sample and test stimuli presented in the right or left visual fields, respectively, were identical. In the control task, subjects were instructed to press a key on every second presentation of the test stimulus. Both discrimination tasks activated the same area in the inferior temporal sulcus of the left hemisphere. The results indicate that the left inferior temporal cortex plays a dominant role in the discrimination of visual pattern in right handed subjects.

Structural divisions and functional fields in the human cerebral cortex

The question of what is a cortical area needs a thorough definition of borders both in the microstructural and the functional domains. Microstructural parcellation of the human cerebral cortex should be made on multiple criteria based on quantitative measurements of microstructural variables, such as neuron densities, neurotransmitter receptor densities, enzyme densities, etc. Because of the inter-individual variations of extent and topography of microstructurally defined areas, the final microstructurally defined areas appear as population maps. In the functional domain, columns, patches and blobs signifying synaptically active parts of the cortex appear as cortical functional fields. These fields are the largest functional entities of the cerebral cortex according to the cortical field hypothesis. In its strong version, the cortical field hypothesis postulates that all neurons and synapses within the fields perform a co-operative computation. A number of such fields together provide the functional contribution of the cerebral cortex. The functional parcellation of the human cerebral cortex must be based on field population maps, which after intersection analysis appear as functional domains. The major structural-functional hypothesis to be examined is whether these functional domains are equi-territorial to the microstructurally defined meta-maps. The cortical hypothesis predicts that, if two brain tasks make use of one or several identical or largely overlapping fields, they cannot be performed simultaneously without errors or increases in latency. Evidence for such interference is presented. This evidence represents a restriction in the parallel processing of the human brain. In the posterior part of the brain not only visual cortical areas may qualify for parallel processing, but also the somatosensory cortices appear to have separate functional streams for the detection of microgeometry and macrogeometry.

Interference between two concurrent tasks is associated with activation of overlapping fields in the cortex

Interference between two concurrent tasks can be measured as an increased reaction time during simultaneous performance compared to when each task is performed alone. We tested the hypothesis that two tasks interfere because they require activation of overlapping areas of the cerebral cortex. With positron emission tomography we measured cortical activation as fields with significant increase in regional cerebral blood flow during single task performance of an auditory and a visual go/no-go task and an auditory and a visual short-term memory (STM) task. In a separate experiment we measured the degree of interference between the two go/no-go tasks and between the two STM tasks during dual task performance. Both the two go/no-go tasks and the two STM tasks activated overlapping parts of the cortex and interfered significantly during dual task performance. The two STM tasks had a larger volume of overlap and also significantly larger increase in reaction time during dual task performance, compared to the go/no-go tasks. The results thus indicate that two concurrent tasks interfere, with a resulting increase in reaction time, if they require activation of overlapping parts of the cortex.

Prediction and preparation, fundamental functions of the cerebellum

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Brainstem, cerebellar and limbic neuroanatomical abnormalities in autism

Recent autopsy and/or quantitative magnetic resonance imaging studies of autistic patients have identified agenesis of the superior olive, dysgenesis of the facial nucleus, reduced numbers of Purkinje neurons, hypoplasia of the brainstem and posterior cerebellum, and increased neuron-packing density of the medial, cortical and central nuclei of the amygdala and the medial septum. As neurogenesis occurs for these different neuron types during approximately the fifth week of gestation, the possibility is raised that this may be a 'window of vulnerability' for autism; the likely etiologic heterogeneity of autism suggests that other windows of vulnerability are also possible.

Attentional activation of the cerebellum independent of motor involvement

The cerebellum traditionally has been viewed as a neural device dedicated to motor control. Although recent evidence shows that it is involved in nonmotor operations as well, an important question is whether this involvement is independent of motor control and motor guidance. Functional magnetic resonance imaging was used to demonstrate that attention and motor performance independently activate distinct cerebellar regions. These findings support a broader concept of cerebellar function, in which the cerebellum is involved in diverse cognitive and noncognitive neurobehavioral systems, including the attention and motor systems, in order to anticipate imminent information acquisition, analysis, or action.