Neural basis of mental scanning of a topographic representation built from a text

Predicted disconnectome associated with progressive periventricular white matter ischemia

We used a virtual lesion DTI fiber tracking approach with healthy subject DTI data and simulated periventricular white matter (PVWM) lesion masks to predict the sequence of connectivity changes associated with progressive PVWM ischemia. We found that the optic radiations, inferior fronto-occipital fasciculus, inferior longitudinal fasciculus, corpus callosum, temporopontine tract and fornix were affected in early simulated ischemic injury, and that the connectivity of subcortical, cerebellar, and visual regions were significantly disrupted with increasing simulated lesion severity. The results of this study provide insights into the spatial-temporal changes of the brain structural connectome under progressive PVWM ischemia. The virtual lesion approach provides a meaningful proxy to the spatial-temporal changes of the brain's structural connectome and can be used to further characterize the cognitive sequelae of progressive PVWM ischemia in both normal aging and dementia.

Recurrence quantification analysis of eye movements during mental imagery

Several studies demonstrated similarities of eye fixations during mental imagery and visual perception but-to our knowledge-the temporal characteristics of eye movements during imagery have not yet been considered in detail. To fill this gap, the same data is analyzed with conventional spatial techniques such as analysis of areas of interest (AOI), ScanMatch, and MultiMatch and with recurrence quantification analysis (RQA), a new way of analyzing gaze data by tracking re-fixations and their temporal dynamics. Participants viewed and afterwards imagined three different kinds of pictures (art, faces, and landscapes) while their eye movements were recorded. While fixation locations during imagery were related to those during perception, participants returned more often to areas they had previously looked at during imagery and their scan paths were more clustered and more repetitive when compared to visual perception. Furthermore, refixations of the same area occurred sooner after initial fixation during mental imagery. The results highlight not only content-driven spatial similarities between imagery and perception but also shed light on the processes of mental imagery maintenance and interindividual differences in these processes.

Does Proprioception Influence Human Spatial Cognition? A Study on Individuals With Massive Deafferentation

When navigating in a spatial environment or when hearing its description, we can develop a mental model which may be represented in the central nervous system in different coordinate systems such as an egocentric or allocentric reference frame. The way in which sensory experience influences the preferred reference frame has been studied with a particular interest for the role of vision. The present study investigated the influence of proprioception on human spatial cognition. To do so, we compared the abilities to form spatial models of two rare participants chronically deprived of proprioception (GL and IW) and healthy control participants. Participants listened to verbal descriptions of a spatial environment, and their ability to form and use a mental model was assessed with a distance-comparison task and a free-recall task. Given that the loss of proprioception has been suggested to specifically impair the egocentric reference frame, the deafferented individuals were expected to perform worse than controls when the spatial environment was described in an egocentric reference frame. Results revealed that in both tasks, one deafferented individual (GL) made more errors than controls while the other (IW) made less errors. On average, both GL and IW were slower to respond than controls, and reaction time was more variable for IW. Additionally, we found that GL but not IW was impaired compared to controls in visuo-spatial imagery, which was assessed with the Minnesota Paper Form Board Test. Overall, the main finding of this study is that proprioception can influence the time necessary to use spatial representations while other factors such as visuo-spatial abilities can influence the capacity to form accurate spatial representations.

Hippocampal spatial mechanisms relate to the development of arithmetic symbol processing in children

Understanding the meaning of abstract mathematical symbols is a cornerstone of arithmetic learning in children. Studies have long focused on the role of spatial intuitions in the processing of numerals. However, it has been argued that such intuitions may also underlie symbols that convey fundamental arithmetic concepts, such as arithmetic operators. In the present cross-sectional study, we used fMRI to investigate how and when associations between arithmetic operators and brain regions processing spatial information emerge in children from 3^rd to 10^th grade. We found that the mere perception of a ‘+’ sign elicited grade-related increases of spatial activity in the right hippocampus. That is, merely perceiving ‘+’ signs – without any operands – elicited enhanced hippocampal activity after around 7^th grade (12–13 years old). In these children, hippocampal activity in response to a ‘+’ sign was further correlated with the degree to which calculation performance was facilitated by the preview of that sign before an addition problem, an effect termed operator-priming. Grade-related increases of hippocampal spatial activity were operation-specific because they were not observed with ‘×’ signs, which might evoke rote retrieval rather than numerical manipulation. Our study raises the possibility that hippocampal spatial mechanisms help build associations between some arithmetic operators and space throughout age and/or education.

Allocentric Spatial Performance Higher in Early-Blind and Sighted Adults Than in Retinopathy-of-Prematurity Adults

The question as to whether people totally blind since infancy process allocentric or external spatial information like the sighted has caused considerable debate within the literature. Due to the extreme rarity of the population, researchers have often included individuals with retinopathy of prematurity (RoP--over oxygenation at birth) within the sample. However, RoP is inextricably confounded with prematurity per se. Prematurity, without visual disability, has been associated with spatial processing difficulties. In this experiment, blindfolded sighted participants and two groups of functionally totally blind participants heard text descriptions from a survey (allocentric) or route (egocentric) perspective. One blind group lost their sight due to RoP and a second group before 24 months of age. The accuracy of participants' mental representations derived from the text descriptions was assessed via questions and maps. The RoP participants had lower scores than the sighted and early blind, who performed similarly. In other words, it was not visual impairment alone that resulted in impaired allocentric spatial performance in this task but visual impairment together with RoP. This finding may help explain the contradictions within the existing literature on the role of vision in allocentric spatial processing.

View-based organization and interplay of spatial working and long-term memories

Space perception provides egocentric, oriented views of the environment from which working and long-term memories are constructed. “Allocentric” (i.e. position-independent) long-term memories may be organized as graphs of recognized places or views but the interaction of such cognitive graphs with egocentric working memories is unclear. Here we present a simple coherent model of view-based working and long-term memories, together with supporting evidence from behavioral experiments. The model predicts that within a given place, memories for some views may be more salient than others, that imagery of a target square should depend on the location where the recall takes place, and that recall favors views of the target square that would be obtained when approaching it from the current recall location. In two separate experiments in an outdoor urban environment, pedestrians were approached at various interview locations and asked to draw sketch maps of one of two well-known squares. Orientations of the sketch map productions depended significantly on distance and direction of the interview location from the target square, i.e. different views were recalled at different locations. Further analysis showed that location-dependent recall is related to the respective approach direction when imagining a walk from the interview location to the target square. The results are consistent with a view-based model of spatial long-term and working memories and their interplay.

Assessing mental imagery in clinical psychology: a review of imagery measures and a guiding framework

Mental imagery is an under-explored field in clinical psychology research but presents a topic of potential interest and relevance across many clinical disorders, including social phobia, schizophrenia, depression, and post-traumatic stress disorder. There is currently a lack of a guiding framework from which clinicians may select the domains or associated measures most likely to be of appropriate use in mental imagery research. We adopt an interdisciplinary approach and present a review of studies across experimental psychology and clinical psychology in order to highlight the key domains and measures most likely to be of relevance. This includes a consideration of methods for experimentally assessing the generation, maintenance, inspection and transformation of mental images; as well as subjective measures of characteristics such as image vividness and clarity. We present a guiding framework in which we propose that cognitive, subjective and clinical aspects of imagery should be explored in future research. The guiding framework aims to assist researchers in the selection of measures for assessing those aspects of mental imagery that are of most relevance to clinical psychology. We propose that a greater understanding of the role of mental imagery in clinical disorders will help drive forward advances in both theory and treatment.

Hyperbole, abstract motion and spatial knowledge: sequential versus simultaneous scanning

Hyperbole is an interesting trope in the perspective of Space Grammar, since it is related to the displacing of a limit (Lausberg in Elemente der literarischen Rhetorik. M.H. Verlag, Munchen 1967; see the Ancient Greek meaning 'to throw over' > 'exaggerate'). Hyperbole semantic mechanisms are related to virtual scanning (Holmqvist and Płuciennik in Imagery in language. Peter Lang, Frankfurt am Main, pp 777-785, 2004). Basic concepts of SIZE and QUANTITY, related image-schemas (IS) and conceptual metaphors (UP IS MORE; IMPORTANT IS BIG: Lakoff 1987, Johnson 1987) are implied in hyperbole processing. The virtual scanning is the simulation of a perceptual domain (here, the vertically oriented space). The virtual limit is defined by expected values on the relevant scale. Since hyperbole is a form of intensification, its linguistic interest lies in cases involving the extremes of a scale, for which a limit can be determined (Schemann 1994). In this experimental study, we analyze the concept of 'limit' in terms of 'abstract motion' and 'oriented space' domains (Langacker 1990) with respect to hyperboles expressed by Italian Verbs of movement. The IS considered are PATH and SOURCE-PATH-GOAL. The latter corresponds to a virtual scale whose limit is arrived at, or overcome, in hyperboles.

Vestibular information is necessary for maintaining metric properties of representational space: evidence from mental imagery

The vestibular system contributes to a wide range of functions, from postural and oculomotor reflexes to spatial representation and cognition. Vestibular signals are important to maintain an internal, updated representation of the body position and movement in space. However, it is not clear to what extent they are also necessary to mentally simulate movement in situations that do not involve displacements of the body, as in mental imagery. The present study assessed how vestibular loss can affect object-based mental transformations (OMTs), i.e., imagined rotations or translations of objects relative to the environment. Participants performed one task of mental rotation of 3D-objects and two mental scanning tasks dealing with the ability to build and manipulate mental images that have metric properties. Menière's disease patients were tested before unilateral vestibular neurotomy and during the recovery period (1 week and 1 month). They were compared to healthy participants tested at similar time intervals and to bilateral vestibular-defective patients tested after the recovery period. Vestibular loss impaired all mental imagery tasks. Performance varied according to the extent of vestibular loss (bilateral patients were frequently the most impaired) and according to the time elapsed after unilateral vestibular neurotomy (deficits were stronger at the early stage after neurotomy and then gradually compensated). These findings indicate that vestibular signals are necessary to perform OMTs and provide the first demonstration of the critical role of vestibular signals in processing metric properties of mental representations. They suggest that vestibular loss disorganizes brain structures commonly involved in mental imagery, and more generally in mental representation.

Mental scanning of sonifications reveals flexible encoding of nonspeech sounds and a universal per-item scanning cost

A mental scanning paradigm was used to examine the representation of nonspeech sounds in working memory. Participants encoded sonifications - nonspeech auditory representations of quantitative data - as either verbal lists, visuospatial images, or auditory images. The number of tones and overall frequency changes in the sonifications were also manipulated to allow for different hypothesized patterns of reaction times across encoding strategies. Mental scanning times revealed different patterns of reaction times across encoding strategies, despite the fact that all internal representations were constructed from the same nonspeech sound stimuli. Scanning times for the verbal encoding strategy increased linearly as the number of items in the verbal representation increased. Scanning times for the visuospatial encoding strategy were generally slower and increased as the metric distance (derived metaphorically from frequency change) in the mental image increased. Scanning times for the auditory imagery strategy were faster and closest to the veridical durations of the original stimuli. Interestingly, the number of items traversed in scanning a representation significantly affected scanning times across all encoding strategies. Results suggested that nonspeech sounds can be flexibly represented, and that a universal per-item scanning cost persisted across encoding strategies. Implications for cognitive theory, the mental scanning paradigm, and practical applications are discussed.

The neural correlates of strategic reading comprehension: cognitive control and discourse comprehension

Neuroimaging studies of text comprehension conducted thus far have shed little light on the brain mechanisms underlying strategic learning from text. Thus, the present study was designed to answer the question of what brain areas are active during performance of complex reading strategies. Reading comprehension strategies are designed to improve a reader's comprehension of a text. For example, self-explanation is a complex reading strategy that enhances existing comprehension processes. It was hypothesized that reading strategies would involve areas of the brain that are normally involved in reading comprehension along with areas that are involved in strategic control processes because the readers are intentionally using a complex reading strategy. Subjects were asked to reread, paraphrase, and self-explain three different texts in a block design fMRI study. Activation was found in both executive control and comprehension areas, and furthermore, learning from text was associated with activation in the anterior prefrontal cortex (aPFC). The authors speculate that the aPFC may play a role in coordinating the internal and external modes of thought that are necessary for integrating new knowledge from texts with prior knowledge.

Impact of the virtual reality on the neural representation of an environment

Despite the increasing use of virtual reality, the impact on cerebral representation of topographical knowledge of learning by virtual reality rather than by actual locomotion has never been investigated. To tackle this challenging issue, we conducted an experiment wherein participants learned an immersive virtual environment using a joystick. The following day, participants' brain activity was monitored by functional magnetic resonance imaging while they mentally estimated distances in this environment. Results were compared with that of participants performing the same task but having learned the real version of the environment by actual walking. We detected a large set of areas shared by both groups including the parieto-frontal areas and the parahippocampal gyrus. More importantly, although participants of both groups performed the same mental task and exhibited similar behavioral performances, they differed at the brain activity level. Unlike real learners, virtual learners activated a left-lateralized network associated with tool manipulation and action semantics. This demonstrated that a neural fingerprint distinguishing virtual from real learning persists when subjects use a mental representation of the learnt environment with equivalent performances.

Grammatical aspect and mental simulation

When processing sentences about perceptible scenes and performable actions, language understanders activate perceptual and motor systems to perform mental simulations of those events. But little is known about exactly what linguistic elements activate modality-specific systems during language processing. While it is known that content words, like nouns and verbs, influence the content of a mental simulation, the role of grammar is less well understood. We investigate the role of grammatical markers in mental simulation through two experiments in which we manipulate the meanings of sentences by modifying the grammatical aspect they use. Using the Action-sentence Compatibility Effect (ACE) methodology [Glenberg, A., Kaschak, M. (2002). Grounding language in action. Psychonomic Bulletin and Review, 9, 558-565], we show that progressive sentences about hand motion facilitate manual action in the same direction, while perfect sentences that are identical in every way except their aspect do not. The broader implication of this finding for language processing is that while content words tell understanders what to mentally simulate and what brain regions to use in performing these simulations, grammatical constructions such as aspect modulate how those simulations are performed.

Global synchronization in the theta band during mental imagery of navigation in humans

Visual mental imagery is critical for successfully navigating the environment, which in turn activates many cortical regions simultaneously. Theta oscillation is implicated in navigation and brain synchronization. In this study, EEG coherence was analyzed during 3 tasks: subjects (1) mentally simulated jogging along the walls of a gym and pressed a button when they imagined arriving at a corner (jogging imagery task), (2) thought of and memorized one digit after pressing a button 5 times and recalled the digits sequentially after pressing the button again (digit imagery task), and (3) pressed a button (button pressing task). The results indicated that theta-wave (4-8 Hz) power was significantly higher in the frontal and parietal regions during the digit and jogging imagery tasks. Coherence at the theta band showed almost no differences between the button pressing and digit imagery tasks. Coherence between the distant regions, especially between the frontal and parieto-occipital regions and between interhemispheric regions, was significantly higher during the jogging imagery task. Increase in theta power during the jogging imagery task reflects working memory load to manipulate internal information. Theta oscillation appears to play an important role in large-scale synchronization to form the functional neuronal networks required for mental navigation.

The Common Neural Basis of Autobiographical Memory, Prospection, Navigation, Theory of Mind, and the Default Mode: A Quantitative Meta-analysis

A core brain network has been proposed to underlie a number of different processes, including remembering, prospection, navigation, and theory of mind [Buckner, R. L., & Carroll, D. C. Self-projection and the brain. Trends in Cognitive Sciences, 11, 49–57, 2007]. This purported network—medial prefrontal, medial-temporal, and medial and lateral parietal regions—is similar to that observed during default-mode processing and has been argued to represent self-projection [Buckner, R. L., & Carroll, D. C. Self-projection and the brain. Trends in Cognitive Sciences, 11, 49–57, 2007] or scene-construction [Hassabis, D., & Maguire, E. A. Deconstructing episodic memory with construction. Trends in Cognitive Sciences, 11, 299–306, 2007]. To date, no systematic and quantitative demonstration of evidence for this common network has been presented. Using the activation likelihood estimation (ALE) approach, we conducted four separate quantitative meta-analyses of neuroimaging studies on: (a) autobiographical memory, (b) navigation, (c) theory of mind, and (d) default mode. A conjunction analysis between these domains demonstrated a high degree of correspondence. We compared these findings to a separate ALE analysis of prospection studies and found additional correspondence. Across all domains, and consistent with the proposed network, correspondence was found within the medial-temporal lobe, precuneus, posterior cingulate, retrosplenial cortex, and the temporo-parietal junction. Additionally, this study revealed that the core network extends to lateral prefrontal and occipital cortices. Autobiographical memory, prospection, theory of mind, and default mode demonstrated further reliable involvement of the medial prefrontal cortex and lateral temporal cortices. Autobiographical memory and theory of mind, previously studied as distinct, exhibited extensive functional overlap. These findings represent quantitative evidence for a core network underlying a variety of cognitive domains.

Encoding modality and spatial memory retrieval

This study examined the temporal characteristics of event-related brain electrical activity associated with the processing of spatial memories derived from linguistic and tactile information. Participants learned a map by (1) reading a text description of the map, (2) touching a wooden topological representation of the map (hidden from view), or (3) both. Subsequently, the participants' ability to use their spatial knowledge was tested in a spatial orientation task. Differential patterns of brain activity as a function of encoding modality were found at the very early (preconscious) stages of processing. In contrast, an analysis of behavioral performance revealed no differences between the encoding groups. A model of spatial memory retrieval is presented to account for the findings.

Language is shaped for social interactions, as well as by the brain

Language learning is not primarily driven by a motivation to describe invariant features of the world, but rather by a strong force to be a part of the social group, which by definition is not invariant. It is not sufficient for language to be fit for the speaker's perceptual motor system. It must also be fit for social interactions.

Accessing the mental space-Spatial working memory processes for language and vision overlap in precuneus

The "overlapping systems" theory of language function argues that linguistic meaning construction crucially relies on contextual information provided by "nonlinguistic" cognitive systems, such as perception and memory. This study examines whether linguistic processing of spatial relations established by reading sentences call on the same posterior parietal neural system involved in processing spatial relations set up through visual input. Subjects read simple sentences, which presented two agents in relation to each other, and were subsequently asked to evaluate spatial (e.g., "Was he turned towards her?") and equally concrete nonspatial content (e.g., "Was he older than her?"). We found that recall of the spatial content relative to the nonspatial content resulted in higher BOLD response in a dorsoposterior network of brain regions, most significantly in precuneus, strikingly overlapping a network previously shown to be involved in recall of spatial aspects of images depicting similar scenarios. This supports a neurocognitive model of language function, where sentences establish meaning by interacting with the perceptual and working memory networks of the brain.

Assessing the symbolic distance effect in mental images constructed from verbal descriptions: a study of individual differences in the mental comparison of distances

In two experiments, undergraduates processed a verbal description of a spatial configuration on the periphery of which six landmarks were located. The participants were then invited to generate visual images of the configuration, and to visualize the distances between pairs of landmarks. Their task consisted of deciding which of the two specified distances was longer. The results showed that as the magnitude of the differences in distance increased, the frequency of correct responses was higher, and response times were shorter. This pattern of results is characteristic of the symbolic distance effect, which is especially interesting in the present experiment where the images generated by the participants were constructed after processing a verbal description (rather than reconstructed from previous perceptual experience). In order to assess the role of visual imagery in the comparison of distances, the performance of participants with the highest scores on a visuo-spatial test (the Minnesota Paper Form Board) was compared to that of those with the lowest scores. High visuo-spatial imagers had higher frequencies of correct responses and shorter response times than the low imagers in the distance-comparison task. They outperformed their counterparts even more clearly on the items where the distance differences were the smallest, suggesting that visual imagery is especially important for items requiring the most attentive examination of a visual image. These data are interpreted as reflecting the fact that visual imagery mediates the process of mentally comparing distances, even when learning has been essentially based on verbal input. These findings support the view that a representation constructed from a verbal description may incorporate metric information about distances, and they offer evidence suggesting that visual images constructed from descriptive texts have genuine analog properties.

The timecourse of activation within the cortical network associated with visual imagery

The current study examined the hemodynamic timecourse of activation within a network of regions that is thought to be associated with visual imagery. Two experimental conditions were examined that were designed to place differential demands on specific nodes within the visual imagery network. The two tasks were an object inspection task and a mental rotation task. The two conditions recruited overlapping cortical regions; however several regions revealed a differential response to object inspection and mental rotation. The mental rotation condition elicited greater activation in parietal cortex, lateral occipital/temporal regions, and bilateral prefrontal cortex. Conversely, the object inspection condition elicited greater activation in inferior extrastriate cortex, the inferior frontal gyrus, and the right cerebellum. When examining the timecourse of activation three different timecourse patterns were observed across cortical regions and conditions. The shape of the hemodynamic timecourse appears to correspond strongly with the cognitive processing taking place within the region, not the stimulus paradigm. The paper discusses the significance of those varying timecourse shapes and has implications for the appropriateness of using the canonical hrf during fMRI data analysis.

Sentence comprehension in autism: thinking in pictures with decreased functional connectivity

Comprehending high-imagery sentences like The number eight when rotated 90 degrees looks like a pair of eyeglasses involves the participation and integration of several cortical regions. The linguistic content must be processed to determine what is to be mentally imaged, and then the mental image must be evaluated and related to the sentence. A theory of cortical underconnectivity in autism predicts that the interregional collaboration required between linguistic and imaginal processing in this task would be underserved in autism. This functional MRI study examined brain activation in 12 participants with autism and 13 age- and IQ-matched control participants while they processed sentences with either high- or low-imagery content. The analysis of functional connectivity among cortical regions showed that the language and spatial centres in the participants with autism were not as well synchronized as in controls. In addition to the functional connectivity differences, there was also a group difference in activation. In the processing of low-imagery sentences (e.g. Addition, subtraction and multiplication are all math skills), the use of imagery is not essential to comprehension. Nevertheless, the autism group activated parietal and occipital brain regions associated with imagery for comprehending both the low and high-imagery sentences, suggesting that they were using mental imagery in both conditions. In contrast, the control group showed imagery-related activation primarily in the high-imagery condition. The findings provide further evidence of underintegration of language and imagery in autism (and hence expand the understanding of underconnectivity) but also show that people with autism are more reliant on visualization to support language comprehension.

Parallel memory systems for talking about location and age in precuneus, caudate and Broca's region

Language comprehension relies on processing of context. Working memory (WM) evoked by linguistic cues for spatial and nonspatial aspects of a visual scene was investigated by correlating fMRI BOLD signal (or 'activation') with reaction times (RTs). Subjects were asked to indicate either the relative positions or ages of people or objects (referenced by the personal pronouns "he/she/it") in a previously shown image. Good performers of a particular task showed shorter RTs than poor performers. Task-specific activation that is greater in good performers than poor ones is taken to indicate involvement of a given region in performance of the task. Our results indicate that dorsoposterior precuneus supports spatial WM during linguistic processing while a network of areas including the caudate support nonspatial WM in categorization of age. We argue that within-subjects variation of RTs across trials reflects effort. Good performers have higher activity in precuneus as a function of effort compared to poor performers during the spatial task, whereas the opposite is found for the nonspatial task, providing further evidence for specifically spatial WM in dorsoposterior precuneus. Task-independent performance-related modulations of activity were found in Broca's area and amygdala. Broca's area activity increased with effort in both tasks, with a greater increase in good performers than in poor performers, consistent with the region's general role in verbal WM. By contrast, activation in amygdala decreased with effort, with a greater decrease in good performers. We take this deactivation to reflect performance-mediating emotional control. These findings indicate that multiple parallel memory systems are available during language processing, appropriate for different tasks, with performance reflecting which system is selected trial-by-trial and subject-by-subject.

Tight covariation of BOLD signal changes and slow ERPs in the parietal cortex in a parametric spatial imagery task with haptic acquisition

The present study investigated the relation of brain activity patterns measured with functional magnetic resonance imaging (fMRI) and slow event-related potentials (ERPs) associated with a complex cognitive task. A second goal was to examine the neural correlates of spatial imagery of haptically--instead of visually--acquired representations. Using a mental image scanning task, spatial imagery requirements were systematically manipulated by parametrically varying the distance between haptically acquired landmarks. Results showed a close relation between slow ERPs and the blood oxygenation level dependent (BOLD) signal in human parietal lobe. Reaction times of mental scanning correlated with the distances between landmarks on the learned display. In parallel, duration and amplitude of slow ERPs and duration of the haemodynamic response systematically varied as a function of mental scanning distance. Source analysis confirmed that the ERP imagery effect likely originated from the same cortical substrate as the corresponding BOLD effect. This covariation of the BOLD signal with slow ERPs is in line with recent findings in animals demonstrating a tight link between local field potentials and the BOLD signal. The parietal location of the imagery effect is consistent with the idea that externally triggered (perceptual) and mentally driven (imagery) spatial processes are both mediated by the same supramodal brain areas.

Two types of image generation: evidence from PET

Is there more than one method whereby people can generate visual mental images? Participants generated images after learning patterns in two ways. In one condition, they memorized descriptions of how segments are arranged to form patterns; in another, they memorized segments and mentally amalgamated them into patterns. In both conditions, identical stimuli cued them to form images while brain activation was monitored using PET. Comparison of the two imagery conditions revealed different activation between hemispheres when images were formed after patterns were learned by mentally combining segments versus when images were formed from stored verbal descriptions. Thus, images can be generated in at least two ways. However, this laterality difference was subtle; the majority of brain areas were activated in common across conditions. This overall similarity is counter to what would be expected if image generation is simply perceptual exploration in the absence of appropriate stimuli, as is posited by perceptual activity theory.

Language in context: emergent features of word, sentence, and narrative comprehension

Context exerts a powerful effect on cognitive performance and is clearly important for language processing, where lexical, sentential, and narrative contexts should differentially engage neural systems that support lexical, compositional, and discourse level semantics. Equally important, but thus far unexplored, is the role of context within narrative, as cognitive demands evolve and brain activity changes dynamically as subjects process different narrative segments. In this study, we used fMRI to examine the impact of context, comparing responses to a single, linguistically matched set of texts when these were differentially presented as random word lists, unconnected sentences and coherent narratives. We found emergent, context-dependent patterns of brain activity in each condition. Perisylvian language areas were always active, consistent with their supporting core linguistic computations. Sentence processing was associated with expanded activation of the frontal operculum and temporal poles. The same stimuli presented as narrative evoked robust responses in extrasylvian areas within both hemispheres, including precuneus, medial prefrontal, and dorsal temporo-parieto-occipital cortices. The right hemisphere was increasingly active as contextual complexity increased, maximal at the narrative level. Furthermore, brain activity was dynamically modulated as subjects processed different narrative segments: left hemisphere activity was more prominent at the onset, and right hemisphere more prominent at the resolution of a story, at which point, it may support a coherent representation of the narrative as a whole. These results underscore the importance of studying language in an ecologically valid context, suggesting a neural model for the processing of discourse.

Hippocampal contributions to neurocognitive mapping in humans: A new model

The ability of an organism to develop, maintain, and act upon an abstracted internal representation of spatially extensive environments can provide an increased chance in ensuring that organism's survival. Here, we propose a neurocognitive model of spatial representation describing how several different processes interact and segregate the differing types of information used to produce a unified cognitive map. This model proposes that view-based egocentric and vestibulomotor translational information are functionally and anatomically separate, and that these parallel systems result in independent, but interacting, models within a neurocognitive map of space. In this context, we selectively review relevant portions of the large literature, addressing the establishment and operation of such spatial constructs in humans and the brain systems that underpin them, with particular reference to the hippocampal formation (HF). We present a reinterpretation of the types of knowledge used in the formation of this spatial construct, the processes that act upon this information, the nature of the final spatial representation, and describe how these universal concepts relate to the proposed model of spatial processing. The relevant experimental paradigms used to examine the neural basis of spatial representation and the main findings from previous research are also briefly presented. Finally, we detail a series of testable theoretical, behavioral, and anatomical predictions made by the model.

Brain areas underlying visual mental imagery and visual perception: an fMRI study

We used functional magnetic resonance imaging (fMRI) to assess the maximal degree of shared neural processing in visual mental imagery and visual perception. Participants either visualized or saw faint drawings of simple objects, and then judged specific aspects of the drawings (which could only be evaluated properly if they used the correct stimulus). The results document that visual imagery and visual perception draw on most of the same neural machinery. However, although the vast majority of activated voxels were activated during both conditions, the spatial overlap was neither complete nor uniform; the overlap was much more pronounced in frontal and parietal regions than in temporal and occipital regions. This finding may indicate that cognitive control processes function comparably in both imagery and perception, whereas at least some sensory processes may be engaged differently by visual imagery and perception.

Left planum temporale: an anatomical marker of left hemispheric specialization for language comprehension

We report on a study aimed at investigating the relationships between handedness, anatomical data and functional data related to speech processing. Twenty subjects with variable handedness (Edinburgh score ranging from -100 to 100) underwent both anatomical magnetic resonance imaging (MRI) and Positron Emission Tomography (PET) during story listening and rest. The surface areas of the left and right planum temporale (PT) were measured on each subject's MRI scan. A multiple regression analysis of PET data was conducted using these PT surface areas as well as handedness scores as predictors. The surface of the left PT explained a significant part of the functional variability. We observed that subjects who had the larger left PT were likely to show a larger leftward functional asymmetry of several perisylvian areas, namely the inferior parietal lobule outside the supra-marginal gyrus (the angular gyrus and the cortex above), Heschl's gyrus, the rolandic operculum, and the temporal pole. The size of the right PT explained only a little part of functional variability and we found no evidence that the anatomical asymmetry of the PT explained functional variability. In addition, we could not evidence any relationship between handedness and functional data. These results, which confirm previous work, argue for a perceptive origin of hemispheric specialization for language comprehension as has been suggested by others.

Imagery in sentence comprehension: an fMRI study

This study examined brain activation while participants read or listened to high-imagery sentences like The number eight when rotated 90 degrees looks like a pair of spectacles or low-imagery sentences, and judged them as true or false. The sentence imagery manipulation affected the activation in regions (particularly, the intraparietal sulcus) that activate in other mental imagery tasks, such as mental rotation. Both the auditory and visual presentation experiments indicated activation of the intraparietal sulcus area in the high-imagery condition, suggesting a common neural substrate for language-evoked imagery that is independent of the input modality. In addition to exhibiting greater activation levels during the processing of high-imagery sentences, the left intraparietal sulcus also showed greater functional connectivity in this condition with other cortical regions, particularly language processing regions, regardless of the input modality. The comprehension of abstract, nonimaginal information in low-imagery sentences was accompanied by additional activation in regions in the left superior and middle temporal areas associated with the retrieval and processing of semantic and world knowledge. In addition to exhibiting greater activation levels during the processing of low-imagery sentences, this left temporal region also revealed greater functional connectivity in this condition with other left hemisphere language processing regions and with prefrontal regions, regardless of the input modality. The findings indicate that sentence comprehension can activate additional cortical regions that process information that is not specifically linguistic but varies with the information content of the sentence (such as visual or abstract information). In particular, the left intraparietal sulcus area appears to be centrally involved in processing the visual imagery that a sentence can evoke, while activating in synchrony with some core language processing regions.

Functional Equivalence of Spatial Representations Derived From Vision and Language: Evidence From Allocentric Judgments

Past research (e.g., J. M. Loomis, Y. Lippa, R. L. Klatzky, & R. G. Golledge, 2002) has indicated that spatial representations derived from spatial language can function equivalently to those derived from perception. The authors tested functional equivalence for reporting spatial relations that were not explicitly stated during learning. Participants learned a spatial layout by visual perception or spatial language and then made allocentric direction and distance judgments. Experiments 1 and 2 indicated allocentric relations could be accurately reported in all modalities, but visually perceived layouts, tested with or without vision, produced faster and less variable directional responses than language. In Experiment 3, when participants were forced to create a spatial image during learning (by spatially updating during a backward translation), functional equivalence of spatial language and visual perception was demonstrated by patterns of latency, systematic error, and variability.