Association Cortex (association + cortex)

Distribution by Scientific Domains

Selected Abstracts

Sensori-motor experience leads to changes in visual processing in the developing brain

Karin Harman James
Since Broca's studies on language processing, cortical functional specialization has been considered to be integral to efficient neural processing. A fundamental question in cognitive neuroscience concerns the type of learning that is required for functional specialization to develop. To address this issue with respect to the development of neural specialization for letters, we used functional magnetic resonance imaging (fMRI) to compare brain activation patterns in pre-school children before and after different letter-learning conditions: a sensori-motor group practised printing letters during the learning phase, while the control group practised visual recognition. Results demonstrated an overall left-hemisphere bias for processing letters in these pre-literate participants, but, more interestingly, showed enhanced blood oxygen-level-dependent activation in the visual association cortex during letter perception only after sensori-motor (printing) learning. It is concluded that sensori-motor experience augments processing in the visual system of pre-school children. The change of activation in these neural circuits provides important evidence that ,learning-by-doing' can lay the foundation for, and potentially strengthen, the neural systems used for visual letter recognition. [source]

Reciprocal connections between olfactory structures and the cortex of the rostral superior temporal sulcus in the Macaca fascicularis monkey

A. Mohedano-Moriano
Abstract Convergence of sensory modalities in the nonhuman primate cerebral cortex is still poorly understood. We present an anatomical tracing study in which polysensory association cortex located at the fundus and upper bank of the rostral superior temporal sulcus presents reciprocal connections with primary olfactory structures. At the same time, projections from this polysensory area reach multiple primary olfactory centres. Retrograde (Fast Blue) and anterograde (biotinylated dextran,amine and 3H-amino acids) tracers were injected into primary olfactory structures and rostral superior temporal sulcus. Retrograde tracers restricted to the anterior olfactory nucleus resulted in labelled neurons in the rostral portion of the upper bank and fundus of superior temporal sulcus. Injections of biotinylated dextran,amine at the fundus and upper bank of the superior temporal sulcus confirmed this projection by labelling axons in the dorsal and lateral portions of the anterior olfactory nucleus, as well as piriform, periamygdaloid and entorhinal cortices. Retrograde tracer injections at the rostral superior temporal sulcus resulted in neuronal labelling in the anterior olfactory nucleus, piriform, periamygdaloid and entorhinal cortices, thus providing confirmation of the reciprocity between primary olfactory structures and the cortex at the rostral superior temporal sulcus. The reciprocal connections between the rostral part of superior temporal sulcus and primary olfactory structures represent a convergence for olfactory and other sensory modalities at the cortex of the rostral temporal lobe. [source]

Comparative cytoarchitectonic analysis of the human and the macaque ventrolateral prefrontal cortex and corticocortical connection patterns in the monkey

M. Petrides
A comparison of the cytoarchitecture of the human and the macaque monkey ventrolateral prefrontal cortex demonstrated a region in the monkey that exhibits the architectonic characteristic of area 45 in the human brain. This region occupies the dorsal part of the ventrolateral prefrontal convexity just below area 9/46v. Rostroventral to area 45 in the human brain lies a large cortical region labelled as area 47 by Brodmann. The ventrolateral component of this region extending as far as the lateral orbital sulcus has architectonic characteristics similar to those of the ventrolateral prefrontal region labelled by Walker as area 12 in the macaque monkey. We designated this region in both the human and the monkey ventrolateral prefrontal cortex as area 47/12. Thus, area 47/12 designates the specific part of the zone previously labelled as area 47 in the human brain that has the same overall architectonic pattern as that of Walker's area 12 in the macaque monkey brain. The cortical connections of these two areas were examined in the monkey by injecting fluorescent retrograde tracers. Although both area 45 and area 47/12 as defined here had complex multimodal input, they could be differentiated in terms of some of their inputs. Retrograde tracers restricted to area 47/12 resulted in heavy labelling of neurons in the rostral inferotemporal visual association cortex and in temporal limbic areas (i.e. perirhinal and parahippocampal cortex). In contrast, injections of tracers into dorsally adjacent area 45 demonstrated strong labelling in the superior temporal gyrus (i.e. the auditory association cortex) and the multimodal cortex in the upper bank of the superior temporal sulcus. [source]

Dynamic spatial cognition: Components, functions, and modifiability of body schema1

Abstract:, There has been substantial progress towards the understanding of the classical notion of "body schema," with recent advances in experimental methodology and techniques. Mental rotation of the hands can be used as a tool to investigate body schema. Research has shown that implicit motor imagery (i.e., mental simulated movements) can be generated based on the body schema, by combining both stored and incoming sensory information. Multimodal stimulation of peripersonal space has also served as an experimental paradigm for the study of body schema. Perception of peripersonal space is based on body-part-centered space coding that is considered as a manifestation of the body schema, its function being to integrate visual, tactile, and proprioceptive information, and perhaps motor plans as well. By combining such experimental paradigms with neuroimaging and neurophysiological techniques, research has converged to show that the parietal association cortex and premotor cortex are important for the body schema. Multimodal perception of body parts and peripersonal space have been also studied in relation to prism adaptation and tool use effects, indicating a clear modifiability of the body schema. Following prolonged adaptation to reversed vision, a reversed hand representation can be added to the body schema like a tool. The stored component of the body schema may not be established well in young children. But once established it may not be deleted even after an arm is amputated, although it may be weakened. All of these findings help to specify properties of the body schema, its components, functions, and modifiabilities. [source]

Topographical and laminar distribution of cortical input to the monkey entorhinal cortex

A. Mohedano-Moriano
Abstract Hippocampal formation plays a prominent role in episodic memory formation and consolidation. It is likely that episodic memory representations are constructed from cortical information that is mostly funnelled through the entorhinal cortex to the hippocampus. The entorhinal cortex returns processed information to the neocortex. Retrograde tracing studies have shown that neocortical afferents to the entorhinal cortex originate almost exclusively in polymodal association cortical areas. However, the use of retrograde studies does not address the question of the laminar and topographical distribution of cortical projections within the entorhinal cortex. We examined material from 60 Macaca fascicularis monkeys in which cortical deposits of either 3H-amino acids or biotinylated dextran-amine as anterograde tracers were made into different cortical areas (the frontal, cingulate, temporal and parietal cortices). The various cortical inputs to the entorhinal cortex present a heterogeneous topographical distribution. Some projections terminate throughout the entorhinal cortex (afferents from medial area 13 and posterior parahippocampal cortex), while others have more limited termination, with emphasis either rostrally (lateral orbitofrontal cortex, agranular insular cortex, anterior cingulate cortex, perirhinal cortex, unimodal visual association cortex), intermediate (upper bank of the superior temporal sulcus, unimodal auditory association cortex) or caudally (parietal and retrosplenial cortices). Many of these inputs overlap, particularly within the rostrolateral portion of the entorhinal cortex. Some projections were directed mainly to superficial layers (I,III) while others were heavier to deep layers (V,VI) although areas of dense projections typically spanned all layers. A primary report will provide a detailed analysis of the regional and laminar organization of these projections. Here we provide a general overview of these projections in relation to the known neuroanatomy of the entorhinal cortex. [source]

In Vivo Visualization of Senile-Plaque-Like Pathology in Alzheimer's Disease Patients by MR Microscopy on a 7T System

Tsutomu Nakada MD
ABSTRACT BACKGROUND Microscopic application of magnetic resonance imaging (MRI) has entered the era of clinical application. One of the most important targets is the visualization of pathological findings such as senile plaques (SP), in vivo, in patients with Alzheimer's disease (AD). Such an application provides not only the most accurate diagnostic tool for clinicians but also a solid basis for scientists for developing effective treatment and preventive strategies for AD. METHODS Focused microscopic studies were performed on parietal association cortex at the level of the centrum semiovale identified on conventional axial slices using a system constructed based on General Electric Signa LX (Waukesha, WI) equipped with a 900-mm clear bore superconducting magnet operating at 7.0 T in 10 patients (67-83-year old, five males, five females) who fulfilled the NINCD and the SADRDA criteria for probable AD, 10 age-matched controls (71-85-year old, five males, five females), and 20 young adults (22-35-year old, 10 males, 10 females) using a susceptibility weighted imaging (SWI) algorithm. RESULTS SWI microscopy consistently provided images with SP-like pathology extending within the entire parietal cortex in all cases of AD and 2 out of 10 age-matched volunteers. CONCLUSIONS Although the precise mechanisms leading to the higher susceptibility rendering SP-like pathology observable within the cortical mantle are not totally understood, the study unambiguously demonstrated that MR microscopy is capable of directly visualizing cortical pathology in AD patients in vivo. [source]

Retrieving meaning after temporal lobe infarction: The role of the basal language area

David J. Sharp MRCP
During speech comprehension the auditory association cortex in the superior temporal cortex is involved in perceptual analysis of the speech signal, whereas the basal language area in the inferior temporal cortex mediates access to word meaning. Disruption of the interaction between the superior and inferior temporal cortices is one factor that may determine recovery from aphasic stroke. We used positron emission tomography to investigate semantic processing within inferior temporal cortex in control subjects and after infarction involving the superior temporal cortex. In the control group, semantic decision making on clear speech activated both anterior fusiform gyri. Chronic aphasic patients were impaired at the task and demonstrated reduced activation within the left anterior fusiform gyrus. A similar pattern of impaired performance and reduced left anterior fusiform gyrus activation was observed when control subjects heard perceptually degraded speech. Performance in both groups predicted activity in the right anterior fusiform gyrus and the temporal poles, where accuracy linearly correlated with activity. These results demonstrate that the function of the basal language area is sensitive to changes in the quality of perceptual input. In addition, different profiles of response observed in each hemisphere suggest distinct contributions of both left and right inferior temporal cortices to the semantic processing of speech. Ann Neurol 2004 [source]

Neural substrates of tactile object recognition: An fMRI study

Catherine L. Reed
Abstract A functional magnetic resonance imaging (fMRI) study was conducted during which seven subjects carried out naturalistic tactile object recognition (TOR) of real objects. Activation maps, conjunctions across subjects, were compared between tasks involving TOR of common real objects, palpation of "nonsense" objects, and rest. The tactile tasks involved similar motor and sensory stimulation, allowing higher tactile recognition processes to be isolated. Compared to nonsense object palpation, the most prominent activation evoked by TOR was in secondary somatosensory areas in the parietal operculum (SII) and insula, confirming a modality-specific path for TOR. Prominent activation was also present in medial and lateral secondary motor cortices, but not in primary motor areas, supporting the high level of sensory and motor integration characteristic of object recognition in the tactile modality. Activation in a lateral occipitotemporal area associated previously with visual object recognition may support cross-modal collateral activation. Finally, activation in medial temporal and prefrontal areas may reflect a common final pathway of modality-independent object recognition. This study suggests that TOR involves a complex network including parietal and insular somatosensory association cortices, as well as occipitotemporal visual areas, prefrontal, and medial temporal supramodal areas, and medial and lateral secondary motor cortices. It confirms the involvement of somatosensory association areas in the recognition component of TOR, and the existence of a ventrolateral somatosensory pathway for TOR in intact subjects. It challenges the results of previous studies that emphasize the role of visual cortex rather than somatosensory association cortices in higher-level somatosensory cognition. Hum. Brain Mapping 21:236,246, 2004. 2004 Wiley-Liss, Inc. [source]

A role for left temporal pole in the retrieval of words for unique entities

Thomas J. Grabowski
Abstract Both lesion and functional imaging studies have implicated sectors of high-order association cortices of the left temporal lobe in the retrieval of words for objects belonging to varied conceptual categories. In particular, the cortices located in the left temporal pole have been associated with naming unique persons from faces. Because this neuroanatomical-behavioral association might be related to either the specificity of the task (retrieving a name at unique level) or to the possible preferential processing of faces by anterior temporal cortices, we performed a PET imaging experiment to test the hypothesis that the effect is related to the specificity of the word retrieval task. Normal subjects were asked to name at unique level entities from two conceptual categories: famous landmarks and famous faces. In support of the hypothesis, naming entities in both categories was associated with increases in activity in the left temporal pole. No main effect of category (faces vs. landmarks/buildings) or interaction of task and category was found in the left temporal pole. Retrieving names for unique persons and for names for unique landmarks activate the same brain region. These findings are consistent with the notion that activity in the left temporal pole is linked to the level of specificity of word retrieval rather than the conceptual class to which the stimulus belongs. Hum. Brain Mapping 13:199,212, 2001. 2001 Wiley-Liss, Inc. [source]

Repairing the human brain after stroke: I. Mechanisms of spontaneous recovery

Steven C. Cramer MD
Stroke remains a leading cause of adult disability. Some degree of spontaneous behavioral recovery is usually seen in the weeks after stroke onset. Variability in recovery is substantial across human patients. Some principles have emerged; for example, recovery occurs slowest in those destined to have less successful outcomes. Animal studies have extended these observations, providing insight into a broad range of underlying molecular and physiological events. Brain mapping studies in human patients have provided observations at the systems level that often parallel findings in animals. In general, the best outcomes are associated with the greatest return toward the normal state of brain functional organization. Reorganization of surviving central nervous system elements supports behavioral recovery, for example, through changes in interhemispheric lateralization, activity of association cortices linked to injured zones, and organization of cortical representational maps. A number of factors influence events supporting stroke recovery, such as demographics, behavioral experience, and perhaps genetics. Such measures gain importance when viewed as covariates in therapeutic trials of restorative agents that target stroke recovery. Ann Neurol 2008;63:272,287 [source]

Alzheimer's disease versus dementia with Lewy bodies: Cerebral metabolic distinction with autopsy confirmation

Satoshi Minoshima MD
Seeking antemortem markers to distinguish Dementia with Lewy bodies (DLB) and Alzheimer's disease (AD), we examined brain glucose metabolism of DLB and AD. Eleven DLB patients (7 Lewy body variant of AD [LBVAD] and 4 pure diffuse Lewy body disease [DLBD]) who had antemortem position emission tomography imaging and autopsy confirmation were compared to 10 autopsy-confirmed pure AD patients. In addition, 53 patients with clinically-diagnosed probable AD, 13 of whom later fulfilled clinical diagnoses of DLB, were examined. Autopsy-confirmed AD and DLB patients showed significant metabolic reductions involving parietotemporal association, posterior cingulate, and frontal association cortices. Only DLB patients showed significant metabolic reductions in the occipital cortex, particularly in the primary visual cortex (LBVAD ,23% and DLBD ,29% vs AD ,8%), which distinguished DLB versus AD with 90% sensitivity and 80% specificity. Multivariate analysis revealed that occipital metabolic changes in DLB were independent from those in the adjacent parietotemporal cortices. Analysis of clinically-diagnosed probable AD patients showed a significantly higher frequency of primary visual metabolic reduction among patients who fulfilled later clinical criteria for DLB. In these patients, occipital hypometabolism preceded some clinical features of DLB. Occipital hypometabolism is a potential antemortem marker to distinguish DLB versus AD. [source]