Biomedical subjects

Emmanuel A Stamatakis

Publications and source records attributed to Emmanuel A Stamatakis.

9 recordsLinked to original sources

PubMed2006

Conceptual structure modulates anteromedial temporal involvement in processing verbally presented object properties.

Recent research has indicated that anteromedial temporal cortex (including the perirhinal cortex) may function as the endpoint of a hierarchically organized visual object-processing network providing the basis for fine-grained discrimination among objects. The present study examines whether the same system is involved in processing conceptual information when concepts, and their properties, are denoted by words. A lesion-behavior correlational study was conducted in which cortical damage in 21 brain-damaged patients was correlated with behavioral scores in a verbally presented property verification task. Results indicated that the neural correlates of conceptual processing depend on the dynamic interaction between the content of a conceptual representation and the specific demands of the task and that the role of anteromedial temporal cortex in this process is not limited to the visual input modality. The results are consistent with the claim that anteromedial temporal cortex provides the neural structure necessary for the emergence of fine-grained conceptual knowledge about objects, although the region is strongly weighted toward processing of visually based object features.

Adaptation, Physiological↗

PubMed2006

Binding crossmodal object features in perirhinal cortex.

Knowledge of objects in the world is stored in our brains as rich, multimodal representations. Because the neural pathways that process this diverse sensory information are largely anatomically distinct, a fundamental challenge to cognitive neuroscience is to explain how the brain binds the different sensory features that comprise an object to form meaningful, multimodal object representations. Studies with nonhuman primates suggest that a structure at the culmination of the object recognition system (the perirhinal cortex) performs this critical function. In contrast, human neuroimaging studies implicate the posterior superior temporal sulcus (pSTS). The results of the functional MRI study reported here resolve this apparent discrepancy by demonstrating that both pSTS and the perirhinal cortex contribute to crossmodal binding in humans, but in different ways. Significantly, only perirhinal cortex activity is modulated by meaning variables (e.g., semantic congruency and semantic category), suggesting that these two regions play complementary functional roles, with pSTS acting as a presemantic, heteromodal region for crossmodal perceptual features, and perirhinal cortex integrating these features into higher-level conceptual representations. This interpretation is supported by the results of our behavioral study: Patients with lesions, including the perirhinal cortex, but not patients with damage restricted to frontal cortex, were impaired on the same crossmodal integration task, and their performance was significantly influenced by the same semantic factors, mirroring the functional MRI findings. These results integrate nonhuman and human primate research by providing converging evidence that human perirhinal cortex is also critically involved in processing meaningful aspects of multimodal object representations.

Adolescent↗

PubMed2005

Temporal and frontal systems in speech comprehension: an fMRI study of past tense processing.

A prominent issue in cognitive neuroscience is whether language function is instantiated in the brain as a single undifferentiated process, or whether regions of relative specialisation can be demonstrated. The contrast between regular and irregular English verb inflection has been pivotal to this debate. Behavioural dissociations related to different lesion sites in brain-damaged patients suggest that processing regular and irregular past tenses involves different neural systems. Using event-related fMRI in a group of unimpaired young adults, we contrast processing of spoken regular and irregular past tense forms in a same-different judgement task, shown in earlier research with patients to engage left hemisphere language systems. An extensive fronto-temporal network, linking anterior cingulate (ACC), left inferior frontal cortex (LIFC) and bilateral superior temporal gyrus (STG), was preferentially activated for regularly inflected forms. Access to meaning from speech is supported by temporal cortex, but additional processing is required for forms that end in regular inflections, which differentially engage LIFC processes that support morpho-phonological segmentation and grammatical analysis.

Adolescent↗

PubMed2005

Identifying lesions on structural brain images--validation of the method and application to neuropsychological patients.

The study of neuropsychological disorders has been greatly facilitated by the localization of brain lesions on MRI scans. Current popular approaches for the assessment of MRI brain scans mostly depend on the successful segmentation of the brain into grey and white matter. These methods cannot be used effectively with large lesions because lesions usually impair segmentation. We propose a novel, fully automated approach for the delineation of brain lesions on MR scans. This method involves comparing a skull stripped, smoothed, unsegmented T1 images to a control group using the general linear model. We tested this method by using images with simulated lesions of different sizes and images containing real lesions from patients with language deficits. We also tested how varying the size of the Gaussian smoothing kernel affects detection. The simulation was informed by findings of a lesion morphological study also presented here. The proposed method detected simulated lesions effectively in the range of 30--90%<normal signal. Smoothing kernels in the range of 8--12 mm resulted in the most accurate lesion detection. Both artificial and real lesions were optimally detected when the results were uncorrected for multiple comparisons at p<.001. This proposed method produced highly satisfactory results and can be used to generate reproducible detection of lesions.

Adult↗

PubMed2005

Dissociating neuro-cognitive component processes: voxel-based correlational methodology.

Relating behavioural deficits to lesion site has long been an important tool for localising the brain bases of cognitive function. Voxel-based methods, based on statistical analyses of structural brain images, allow a major step forward in the effectiveness of this approach. These methods provide a fine-grained assessment of damaged tissue by assigning a continuous value to each voxel over the entire brain. This information, correlated with continuous behavioural data reflecting specific aspects of cognition, offers new opportunities for identifying the neural organisation underlying cognitive function. The research reported here demonstrates the ability of this correlational methodology to differentiate between the neuro-cognitive components involved in word recognition and lexical decision, providing an important new tool for directly linking brain areas to specific aspects of psychological performance.

Acoustic Stimulation↗

PubMed2004

Deficits for semantics and the irregular past tense: a causal relationship?

The regular and irregular past tense has become a focus for recent debates about the structure of the language processing system, asking whether language functions are subserved by different neural and functional mechanisms or whether all processes can be accommodated within a single unified system. A critical claim of leading single mechanism accounts is that the relationship between an irregular stem and its past tense form is primarily semantic and not morphological in nature. This predicts an obligatory relationship between semantic performance and access to the irregular past tense, such that a semantic deficit necessarily leads to impairments on the irregulars. We tested this claim in a series of studies probing the comprehension and production of regular and irregular past tense forms in four semantic dementia patients, all of whom had profound semantic deficits. In two elicitation tasks and one auditory priming study, we found that three out of the four patients did not have a deficit for the irregular past tense, in spite of their semantic deficits. This argues against the view that the relationship between irregular past tense forms and their stems is primarily semantic, and more generally against the single system claim that morphological structure can be captured solely based on phonological and semantic relationships.

Aged↗

PubMed2003

Neuroimaging in eating disorders.

Neuroanatomical and functional studies in the eating disorders (ED) are reviewed. Typically, anorexia nervosa (AN) is associated with cerebral spinal fluid spaces enlargement which generally recover as a function of re-feeding. However, specific cortical areas fail to correct in weight restored anorectic patients suggesting trait-related abnormalities. Functional changes in AN associated with starvation reverse with weight recovery, however, reduced 5-HT2A receptor binding may be fundamental to the pathophysiology of AN since this remains after long term weight restoration. Structural studies of bulimia nervosa (BN) provide evidence of brain atrophy, in the absence of significant weight loss but potentially related to chronic dietary restriction. Functional investigations reveal reduced thalamic and hypothalamic serotonin transporter availability in BN which increases with longer illness duration. Thus, BN is associated with substantial structural and functional alterations despite normal weight. Recent advances in neuroimaging techniques and their interpretation are increasing our understanding of normal processes in the control of food intake including neuroanatomical correlates of hunger and satiety. Taken together with the structural and functional changes observed in the ED, neuroimaging provides a powerful platform to identify the underlying trait-related pathophysiological mechanisms in the aetiology and maintenance of AN and BN.

Anorexia Nervosa↗

PubMed2002

SPECT imaging in head injury interpreted with statistical parametric mapping.

UNLABELLED: This study investigated regional cerebral blood flow in head-injured patients using statistical parametric mapping (SPM) to detect hypoperfusion on (99m)Tc-hexamethylpropyleneamine oxime (HMPAO) SPECT scans. METHODS: Acute and follow-up SPECT and MRI scans from 61 patients who were admitted to a regional neurosurgical unit were examined. Patients had acute MRI and SPECT at 2-18 d after injury and on follow-up between 130 and 366 d after injury. Thirty-two scans from non-head-injured patients were used as a SPECT control group. The SPECT images were first aligned to the Talairach-Tournoux atlas and then analyzed statistically with SPM. RESULTS: SPECT detected more extensive abnormality than MRI in acute and follow-up stages. This effect was more pronounced on follow-up of patients with diffuse injury. Examination of a focal injury group indicated the involvement of frontal and temporal lobes and the anterior cingulate. Blood flow abnormalities persist, to a lesser extent, on follow-up scans. The diffuse group displayed low blood flow in the frontal and temporal lobes, including cingulate involvement, which persists at follow-up with additional involvement of the thalamus. CONCLUSION: SPM has a role in SPECT image interpretation because it allows better visualization than other methods of quantitative analysis of the spatial distribution of abnormalities in focal and diffuse head injury. Frontal lobe blood flow abnormality (particularly anterofrontal regions and mesiofrontal areas) is common after head injury.

Adolescent↗

PubMedDate not supplied

The anatomy of object processing: the role of anteromedial temporal cortex.

How objects are represented and processed in the brain remains a key issue in cognitive neuroscience. We have developed a conceptual structure account in which category-specific semantic deficits emerge due to differences in the structure and content of concepts rather than from explicit divisions of conceptual knowledge in separate stores. The primary claim is that concepts associated with particular categories (e.g., animals, tools) differ in the number and type of properties and the extent to which these properties are correlated with each other. In this review, we describe recent neuropsychological and neuroimaging studies in which we have extended our theoretical account by incorporating recent claims about the neuroanatomical basis of feature integration and differentiation that arise from research into hierarchical object processing streams in nonhuman primates and humans. A clear picture has emerged in which the human perirhinal cortex and neighbouring anteromedial temporal structures appear to provide the neural infrastructure for making fine-grained discriminations among objects, suggesting that damage within the perirhinal cortex may underlie the emergence of category-specific semantic deficits in brain-damaged patients.

Animals↗