51 research outputs found
EEG-Microstates Reflect Auditory Distraction After Attentive Audiovisual Perception Recruitment of Cognitive Control Networks
Processing of sensory information is embedded into ongoing neural processes which contribute to brain states. Electroencephalographic microstates are semi-stable short-lived power distributions which have been associated with subsystem activity such as auditory, visual and attention networks. Here we explore changes in electrical brain states in response to an audiovisual perception and memorization task under conditions of auditory distraction. We discovered changes in brain microstates reflecting a weakening of states representing activity of the auditory system and strengthening of salience networks, supporting the idea that salience networks are active after audiovisual encoding and during memorization to protect memories and concentrate on upcoming behavioural response
Tracing of temporo-entorhinal connections in the human brain: cognitively impaired argyrophilic grain disease cases show dendritic alterations but no axonal disconnection of temporo-entorhinal association neurons
Argyrophilic grain disease (AGD), a neurodegenerative disorder, is often associated with mild to moderate Alzheimer’s disease (AD)-related pathology. The development of dementia in AGD is associated with the extent of coexisting AD-related pathology. Therefore, the question arises whether the degenerative changes in the neuronal network of demented AGD-patients represent a distinct pattern or show similar changes of disconnection as considered for AD. We were able to apply DiI-tracing in two human autopsy cases with mild AD-related pathology (controls), in one AD-patient, in one non-demented patient with advanced AD-related pathology, and in three cognitively impaired AGD-patients. DiI-crystals were injected into the entorhinal cortex. Pyramidal neurons of layers III and V of the adjacent temporal neocortex (area 35) were retrogradely marked with the tracer and analyzed. The AD case did not exhibit any retrogradely labeled neurons in the temporal neocortex. In the non-demented case with advanced AD-related pathology, the number of traced neurons was reduced as compared to that in the two controls and in the three AGD cases. In contrast, all three cognitively impaired AGD cases exhibited labeled pyramidal neurons in area 35 in an almost similar number as in the controls. However, alterations in the dendritic tree were observed in the AGD cases. These results show the existence of temporo-entorhinal connections in the adult human brain similar to those reported in animal models. Furthermore, the present study based on seven cases is the first attempt to study changes in the neuronal network in a human tauopathy with targeted axonal tracing techniques. Our findings in three cognitively impaired AGD cases suggest that AGD-related dementia constitutes a distinct disorder with a characteristic pattern of degeneration in the neuronal network
Automatic Segmentation of Human Cortical Layer-Complexes and Architectural Areas Using Ex vivo Diffusion MRI and Its Validation
Recently, several magnetic resonance imaging contrast mechanisms have been shown to distinguish cortical substructure corresponding to selected cortical layers. Here, we investigate cortical layer and area differentiation by automatized unsupervised clustering of high-resolution diffusion MRI data. Several groups of adjacent layers could be distinguished in human primary motor and premotor cortex. We then used the signature of diffusion MRI signals along cortical depth as a criterion to detect area boundaries and find borders at which the signature changes abruptly. We validate our clustering results by histological analysis of the same tissue. These results confirm earlier studies which show that diffusion MRI can probe layer-specific intracortical fiber organization and, moreover, suggests that it contains enough information to automatically classify architecturally distinct cortical areas. We discuss the strengths and weaknesses of the automatic clustering approach and its appeal for MR-based cortical histology
Morphological events in the development of long-range intracortical connections in cat visual-cortex
The origin and topography of long-range intrinsic projections in cat visual cortex: a developmental study.
We investigated the morphological features of long range intrinsically projecting neurons and their pattern of axonal arborization in cat area 17 at different stages of postnatal development. In one set of experiments intracortically projecting cells were retrogradely labeled in vivo with rhodamine latex beads and then visualized by in vitro filling with Lucifer yellow. In another approach, intracortical fibers including the cells of origin were labeled postmortem in fixed brains with the lipophilic carbocyanine dye Dil. The results of this study indicate that the long-range intrinsic circuitry of the primary visual cortex develops in three major steps. The first step consists of the development of unclustered long-range axons in the two outer compartments of the cerebral cortex, layer I and the subplate. These early connections could serve as a scaffold for the organization of the tangential architecture of the neocortex as they originate from cells that are the first to receive synaptic input from extrinsic afferents. The second step consists of the outgrowth of horizontal axon collaterals originating from cells located in layers II-VI. During the first 2-3 weeks these connections still differ from those in the adult because they span shorter distances, originate more often from neurons with morphological features of nonpyramidal cells, and lack the precise clustering of the mature connections. The third step consists of a selection process that leads to the elimination of axon terminals from locations between the clusters of tangentially projecting neurons. This selection starts at the end of the second postnatal week and, hence, overlaps in time with the still proceeding elongation of axons and continues beyond the end of the fourth postnatal week when axon length has reached its maximal extent. This refinement process enhances the specificity of long-range connections and is probably influenced by visual experience
Hemispheric asymmetries in cerebral cortical networks.
Since the middle of the 19th century it has been recognized that several higher cognitive functions, including language, are lateralized in cerebral cortex. Neuropsychological studies on patients with brain lesions and rapid developments in brain imaging techniques have provided us with an increasing body of data on the functional aspects of language lateralization, but little is known about the substrate on which these specializations are realized. Much attention has been focused on the gross size and shape of cortical regions involved, but recent findings indicate that the columnar and connectional structure within auditory and language cortex in the left hemisphere are distinct from those in homotopic regions in the right hemisphere. These findings concern parameters that are closely linked to the processing architecture within the respective regions. Thus, the comparison of these microanatomical specializations with their respective functional counterparts provides important insights into the functional role of cerebral cortical organization and its consequences for processing of cortical information in the implementation of complex cognitive functions
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