Cytoarchitectonic Analysis Research Articles

From brain cytoarchitectonics to clinical neurology: Polish Institute for Brain Research in Vilnius, 1931-1938.

The Polish Institute for Brain Research was established in Warsaw in 1928 to support scientific research on the brain and its functions. The director of the institute was Maksymilian Rose (1883-1937), a distinguished Polish neurologist and neuroanatomist, a disciple of Oskar Vogt and Korbinian Brodmann. In 1931, the Institute was moved from Warsaw to Vilnius. The Institute was well-known in Europe at the time because of the research in the fields of neuroscience, clinical neurology, and psychiatry, as well as the cytoarchitectonic analysis of social activists' brains-a fashionable, neophrenological way to link the mental functions of deceased geniuses with the cellular composition of their central nervous systems. In 1939, the work of the Institute was interrupted by World War II; some of the preparations and materials were moved from Vilnius to Warsaw, some were stored in Vilnius, and some were lost. In this article, we analyze the primary and secondary sources, some of which were obscure for over 80years, and evaluate the most important scientific achievements of the Polish Institute for Brain Research, as well as its legacy in the early period of modern neuroscience and neurology in interwar Vilnius.

Specific biomarkers and neurons distribution of different brain regions in largemouth bass (Micropterus salmoides).

The brain regulates multiple physiological processes in fish. Despite this, knowledge about the basic structure and function of distinct brain regions in non-model fish species remains limited due to their diversity and the scarcity of common biomarkers. In the present study, four major brain parts, the telencephalon, diencephalon, mesencephalon and rhombencephalon, were isolated in largemouth bass, Micropterus salmoides. Within these parts, nine brain regions and 74 nuclei were further identified through morphological and cytoarchitectonic analysis. Transcriptome analysis revealed a total of 7153 region-highly expressed genes and 176 region-specifically expressed genes. Genes related to growth, reproduction, emotion, learning, and memory were significantly overexpressed in the olfactory bulb and telencephalon (OBT). Feeding and stress-related genes were in the hypothalamus (Hy). Visual system-related genes were predominantly enriched in the optic tectum (OT), while vision and hearing-related genes were widely expressed in the cerebellum (Ce) region. Sensory input and motor output-related genes were in the medulla oblongata (Mo). Osmoregulation, stress response, sleep/wake cycles, and reproduction-related genes were highly expressed in the remaining brain (RB). Three candidate marker genes were further identified for each brain regions, such as neuropeptide FF (npff) for OBT, pro-melanin-concentrating hormone (pmch) for Hy, vesicular inhibitory amino acid transporter (viaat) for OT, excitatory amino acid transporter 1 (eaat1) for Ce, peripherin (prph) for Mo, and isotocin neurophysin (itnp) for RB. Additionally, the distribution of seven neurotransmitter-type neurons and five types of non-neuronal cells across different brain regions were analyzed by examining the expression of their marker genes. Notably, marker genes for glutamatergic and GABAergic neurons showed the highest expression levels across all brain regions. Similarly, the marker gene for radial astrocytes exhibited high expression compared to other markers, while those for microglia were the least expressed. Overall, our results provide a comprehensive overview of the structural and functional characteristics of distinct brain regions in the largemouth bass, which offers a valuable resource for understanding the role of central nervous system in regulating physiological processes in teleost.

Cytoarchitectonic Analysis and 3D Maps of the Mesial Piriform Region in the Human Brain

The mesial piriform region plays a central role in olfaction. Its small size and complex geometry, however, make it a difficult target in functional neuroimaging studies, while histological maps often represent schematic drawings, which are not compatible with requirements for modern imaging. To bridge this gap, cytoarchitectonic analysis and mapping of the region was performed in serial histological sections over their full extent in 10 postmortem brains. The temporobasal areas PirTBd and PirTBv and temporal areas PirTu and PirTit were identified and analyzed. Probabilistic cytoarchitectonic maps of the piriform areas in MNI reference space and high-resolution maps of the amygdala-piriform region on the BigBrain model were calculated as part of the Julich-Brain. Differences in the cytoarchitectonic “texture” of the region were quantified based on the Gray Level Co-Occurrence Matrix. Results showed that allocortical areas were not consistently associated with the rostral Limen insulae, although it was often suggested as a landmark in neuroimaging protocols. PirTu was associated with the uncal tip. PirTit was the largest area, reaching to the temporal pole, with a “temporal” (caudal) and a “temporopolar” (rostral) part having complex neighborhood relationships. The probabilistic maps reflect interindividual variability; they are openly available via the digital EBRAINS platform to serve as an anatomical reference for studies related to olfaction.

A revised perspective on the evolution of the lateral frontal cortex in primates.

Detailed neuroscientific data from macaque monkeys have been essential in advancing understanding of human frontal cortex function, particularly for regions of frontal cortex without homologs in other model species. However, precise transfer of this knowledge for direct use in human applications requires an understanding of monkey to hominid homologies, particularly whether and how sulci and cytoarchitectonic regions in the frontal cortex of macaques relate to those in hominids. We combine sulcal pattern analysis with resting-state functional magnetic resonance imaging and cytoarchitectonic analysis to show that old-world monkey brains have the same principles of organization as hominid brains, with the notable exception of sulci in the frontopolar cortex. This essential comparative framework provides insights into primate brain evolution and a key tool to drive translation from invasive research in monkeys to human applications.

The inferior frontal sulcus: Cortical segregation, molecular architecture and function

The inferior frontal sulcus is conceptualized as the landmark delineating ventro-from dorsolateral prefrontal cortex. Functional imaging studies report activations within the sulcus during tasks addressing cognitive control and verbal working memory, while their microstructural correlates are not well defined. Existing microstructural maps, e.g., Brodmann's map, do not distinguish separate areas within the sulcus. We identified six new areas in the inferior frontal sulcus and its junction to the precentral sulcus, ifs1-4, ifj1-ifj2, by combined cytoarchitectonic analysis and receptor autoradiography. A hierarchical cluster analysis of receptor densities of these and neighbouring prefrontal areas revealed that they form a distinct cluster within the prefrontal cortex. Major interhemispheric differences were found in both cyto- and receptorarchitecture. The function of cytoarchitectonically identified areas was explored by comparing probabilistic maps of the areas in stereotaxic space with their functions and co-activation patterns as analysed by means of a coordinate-based meta-analysis. We found a bilateral involvement in working memory, as well as a lateralization of different language-related processes to the left hemisphere, and of music processing and attention to the right-hemispheric areas. Particularly ifj2 might act as a functional hub between the networks. The cytoarchitectonic maps and receptor densities provide a powerful tool to further elucidate the function of these areas. The maps are available through the Human Brain Atlas of the Human Brain Project and serve in combination with the information on the cyto- and receptor architecture of the areas as a resource for brain models and simulations.

Investigating the sub-regions of the superior parietal cortex using functional magnetic resonance imaging connectivity

ObjectivesTraditionally, the superior parietal lobule (SPL) is usually investigated as one region of interest, particularly in functional magnetic resonance imaging (fMRI) studies. However, cytoarchitectonic analysis has shown that the SPL has a complex, heterogeneous topology that comprises more than seven sub-regions. Since previous studies have shown how the SPL is significantly involved in different neurological functions—such as visuomotor, cognitive, sensory, higher order, working memory and attention—this study aims to investigate whether these cytoarchitecturally different sub-regions have different functional connectivity to different functional brain networks.MethodsThis study examined 198 healthy subjects using resting-state fMRI and investigated the functional connectivity of seven sub-regions of the SPL to eight regional functional networks.ResultsThe findings showed that most of the seven sub-regions were functionally connected to these targeted networks and that there are differences between these sub-regions and their functional connectivity patterns. The most consistent functional connectivity was observed with the visual and attention networks. There were also clear functional differences between Brodmann area (BA) 5 and BA7. BA5, with its three sub-regions, had strong functional connectivity to both the sensorimotor and salience networks.ConclusionThese findings have enhanced our understanding of the functional organisations of the complexity of the SPL and its varied topology and also provide clear evidence of the functional patterns and involvements of the SPL in major brain functions.

Multimodal mapping and analysis of the cyto- and receptorarchitecture of the human hippocampus

The human hippocampal formation is relevant for various aspects of memory and learning, and the different hippocampal regions are differentially affected by neuropsychiatric disorders. Therefore, the hippocampal formation has been subject of numerous cytoarchitectonic and other mapping studies, which resulted in divergent parcellation schemes. To understand the principles of hippocampal architecture, it is necessary to integrate different levels of hippocampal organisation, going beyond one modality. We here applied a multimodal mapping approach combining cyto- and multi-receptorarchitectonic analyses, and generated probabilistic maps in stereotaxic space of the identified regions. Cytoarchitecture in combination with the regional and laminar distribution of 15 neurotransmitter receptors visualized by in vitro receptor autoradiography were analysed in seven hemispheres from 6 unfixed shock frozen and serially sectioned brains. Cytoarchitectonic delineations for generation of probabilistic maps were carried out on histological sections from ten fixed, paraffin embedded and serially sectioned brains. Nine cyto- and receptorarchitectonically distinct regions were identified within the hippocampal formation (i.e., fascia dentata, cornu Ammonis (CA) regions 1–4, prosubiculum, subiculum proper, presubiculum and parasubiculum), as well as the hippocampal-amygdaloid transition area and the periallocortical transsubiculum. Subsequently generated probabilistic maps quantify intersubject variability in the size and extent of these cyto- and receptorarchitectonically distinct regions. The regions did not differ in their volume between the hemispheres and gender. Receptor mapping revealed additional subdivisions which could not be detected by cytoarchitectonic analysis alone. They correspond to parcellations previously found in immunohistochemical and connectivity studies. The multimodal approach enabled the definition of regions not consistently reported, e.g., CA4 region or prosubiculum. The ensuing detailed probabilistic maps of the hippocampal formation constitute the basis for future architectonically informed analyses of in vivo neuroimaging studies.

Targeted Stimulation of Human Orbitofrontal Networks Disrupts Outcome-Guided Behavior.

Outcome-guided behavior requires knowledge about the current value of expected outcomes. Such behavior can be isolated in the reinforcer devaluation task, which assesses the ability to infer the current value of specific rewards after devaluation. Animal lesion studies demonstrate that orbitofrontal cortex (OFC) is necessary for normal behavior in this task, but a causal role for human OFC in outcome-guided behavior has not been established. Here, we used sham-controlled, non-invasive, continuous theta-burst stimulation (cTBS) to temporarily disrupt human OFC network activity by stimulating a site in the lateral prefrontal cortex that is strongly connected to OFC prior to devaluation of food odor rewards. Subjects in the sham group appropriately avoided Pavlovian cues associated with devalued food odors. However, subjects in the stimulation group persistently chose those cues, even though devaluation of food odors themselves was unaffected by cTBS. This behavioral impairment was mirrored in changes in resting-state functional magnetic resonance imaging (rs-fMRI) activity such that subjects in the stimulation group exhibited reduced OFC network connectivity after cTBS, and the magnitude of this reduction was correlated with choices after devaluation. These findings demonstrate the feasibility of indirectly targeting the human OFC with non-invasive cTBS and indicate that OFC is specifically required for inferring the value of expected outcomes.

Molecular anatomy of the alligator dorsal telencephalon

The evolutionary relationships of the mammalian neocortex and avian dorsal telencephalon (DT) nuclei have been debated for more than a century. Despite their central importance to this debate, nonavian reptiles remain underexplored with modern molecular techniques. Reptile studies harbor great potential for understanding the changes in DT organization that occurred in the early evolution of amniotes. They may also help clarify the specializations in the avian DT, which comprises a massive, cell-dense dorsal ventricular ridge (DVR) and a nuclear dorsal-most structure, the Wulst. Crocodilians are phylogenetically and anatomically attractive for DT comparative studies: they are the closest living relatives of birds and have a strikingly bird-like DVR, but they also possess a highly differentiated reptile cerebral cortex. We studied the DT of the American alligator, Alligator mississippiensis, at late embryonic stages with a panel of molecular marker genes. Gene expression and cytoarchitectonic analyses identified clear homologs of all major avian DVR subdivisions including a mesopallium, an extensive nidopallium with primary sensory input territories, and an arcopallium. The alligator medial cortex is divided into three components that resemble the mammalian dentate gyrus, CA fields, and subiculum in gene expression and topography. The alligator dorsal cortex contains putative homologs of neocortical input, output, and intratelencephalic projection neurons and, most notably, these are organized into sublayers similar to mammalian neocortical layers. Our findings on the molecular anatomy of the crocodilian DT are summarized in an atlas of the alligator telencephalon.

Brodmann Areas 8 and 9 Including the Frontal Eye Field

Based on cytoarchitectonic analyses, Brodmann assigned numbers 8 and 9 to certain areas of the dorsal and medial prefrontal cortex (PFC) in humans and monkeys. Petrides and Pandya re-analyzed the cytoarchitectures of the human and monkey PFCs, and proposed slightly different brain maps for both species. They assigned numbers 8, 9 and 9/46 to the areas that were originally named areas 8 and 9. Areas 8 and 9 have both lateral and medial regions respectively. The lateral area 8 is important for conditional discrimination learning. The frontal eye field which occupies the most caudal region of area 8, is responsible for visual attention and control of eye movements. The lateral area 9 and area 9/46 are functionally similar to area 46 and play important roles in executive control. The dorsomedial prefrontal cortex (DMPFC) comprises the medial regions of areas 8 and 9 and is related to "Theory of Mind" and social cognition. The DMPFC is also known to show "default mode of brain activity" (i.e., more activity during rest than during cognitive task).

THE CYTOARCHITECTONICS AND NEURONAL ORGANIZATION OF THE BASOLATERAL NUCLEUS OF THE AMYGDALA OF THE BRAIN IN ALCOHOL-PREFERRING AND ALCOHOL-NONPREFERRING RATS

Analysis of cytoarchitectonics of the basolateral nucleus (BLN) of the brain amygdala was performed in cresyl violet-stained frontal paraffin sections of the brain in 10 alcohol-preferring (AP) and 10 alcohol-nonpreferring (ANP) rats (with an equal number of male and female animals in each group). The presence of large and small neurons was detected in BLN. Most of the large neurons in AP rats had the character of chromoneutral and moderately chromophilic cells, while in ANP rats these cells were moderately chromophobic. Application of Golgi method demonstrated that the equivalents of large neurons were long-axonal densely branched pyramid-like neurons, and those of small-sized neurons - short-axonal neurons. The determination of the ratio of large and small-sized neurons showed that in AP rats the proportion of latter was 12.3±0.6%, while in the ANP rats it was significantly greater - 19.70±0.23%. These results help to explain the previously obtained data on larger specific area of BLN in amygdala of ANP rats by the presence of greater number of interneurons than in AP rats.

Rescuing Perishable Neuroanatomical Information from a Threatened Biodiversity Hotspot: Remote Field Methods for Brain Tissue Preservation Validated by Cytoarchitectonic Analysis, Immunohistochemistry, and X-Ray Microcomputed Tomography.

Biodiversity hotspots, which harbor more endemic species than elsewhere on Earth, are increasingly threatened. There is a need to accelerate collection efforts in these regions before threatened or endangered species become extinct. The diverse geographical, ecological, genetic, morphological, and behavioral data generated from the on-site collection of an individual specimen are useful for many scientific purposes. However, traditional methods for specimen preparation in the field do not permit researchers to retrieve neuroanatomical data, disregarding potentially useful data for increasing our understanding of brain diversity. These data have helped clarify brain evolution, deciphered relationships between structure and function, and revealed constraints and selective pressures that provide context about the evolution of complex behavior. Here, we report our field-testing of two commonly used laboratory-based techniques for brain preservation while on a collecting expedition in the Congo Basin and Albertine Rift, two poorly known regions associated with the Eastern Afromontane biodiversity hotspot. First, we found that transcardial perfusion fixation and long-term brain storage, conducted in remote field conditions with no access to cold storage laboratory equipment, had no observable impact on cytoarchitectural features of lizard brain tissue when compared to lizard brain tissue processed under laboratory conditions. Second, field-perfused brain tissue subjected to prolonged post-fixation remained readily compatible with subsequent immunohistochemical detection of neural antigens, with immunostaining that was comparable to that of laboratory-perfused brain tissue. Third, immersion-fixation of lizard brains, prepared under identical environmental conditions, was readily compatible with subsequent iodine-enhanced X-ray microcomputed tomography, which facilitated the non-destructive imaging of the intact brain within its skull. In summary, we have validated multiple approaches to preserving intact lizard brains in remote field conditions with limited access to supplies and a high degree of environmental exposure. This protocol should serve as a malleable framework for researchers attempting to rescue perishable and irreplaceable morphological and molecular data from regions of disappearing biodiversity. Our approach can be harnessed to extend the numbers of species being actively studied by the neuroscience community, by reducing some of the difficulty associated with acquiring brains of animal species that are not readily available in captivity.

Dynamics of changes in the structure of the hippocampus in a myocardial dysfunction.

Background. It is well known that cardiovascular disease lead to the disruption of integrative functions of the brain, provided by hippocampus. Objective. To investigate the dynamics of spatial and quantitative pathological changes of hippocampal neurons under experimental myocardial dysfunction. Methods. Brain of male Wistar rats were divided into experimental (injected with doxorubicin) and control (injected with 0.9% solution of NaCl) groups. Results. Brains of rats of the experimental group underwent significant pathological changes in glia, as well as vascular system. In the superficial layers cerebral cortex looked as porous, spongy mesh structure. The vessels of the brain at all levels have demonstrated the phenomena of circulatory disorders in the form of congestion and stasis. Analysis of cytoarchitectonics of the hippocampus of rats in the control group showed significant differences in the quantitative composition of neurons in field CA1, CA3 and dentate gyrus (50,3 ± 1,1; 66,6 ± 0,6 and 60,4 ± 1,1 in R≤ 0.05, respectively). Conclusion. In conditions of experimental myocardial dysfunction in the hippocampus a gradual loss of individual neurons, and rows of cells was revealed. The most sensitive areas of the hippocampus in those conditions was a field CA3, where the total loss of the cellular composition for a period of follow-up was 45.1%. Except quantitative changes of a qualitative change in the form of loss of order neurons, loosening of rows and a violation of the blood supply to the brain vessels was detected.

A new concept of paleoamygdala substrate

We put forward a new concept of paleoamygdala substrate, a complex of gray matter located in the periventricular zone of the lateral ventricle underhorn in the posterior segment of the phylogenetically ancient cortical/medial group of the amygdaloid complex. The argumentation is based on the cytoarchitectonic analysis, the consideration of specific neural organization and ontogenetic features as well as the literature data characterizing the results of hodological and functional studies.

Beyond the silence: Bilateral somatosensory stimulation enhances skilled movement quality and neural density in intact behaving rats

It is thought that a close dialogue between the primary motor (M1) and somatosensory (S1) cortices is necessary for skilled motor learning. The extent of the relative S1 contribution in producing skilled reaching movements, however, is still unclear. Here we used anodal transcranial direct current stimulation (tDCS), which is able to alter polarity-specific excitability in the S1, to facilitate skilled movement in intact behaving rats. We hypothesized that the critical role of S1 in reaching performance can be enhanced by bilateral tDCS. Pretrained rats were assigned to control or stimulation conditions: (1) UnAno: the unilateral application of an anodal current to the side contralateral to the paw preferred for reaching; (2) BiAno1: bilateral anodal current; (3) BiAno2: a bilateral anodal current with additional 30ms of 65μA pulses every 5s. Rats received tDCS (65μA; 10min/rat) to the S1 during skilled reach training for 20 days (online-effect phase). After-effect assessment occurred for the next ten days in the absence of electrical stimulation. Quantitative and qualitative analyses of online-effects of tDCS showed that UnAno and BiAno1 somatosensory stimulation significantly improve skilled reaching performance. Bilateral BiAno1 stimulation was associated with greater qualitative functional improvement than unilateral UnAno stimulation. tDCS-induced improvements were not observed in the after-effects phase. Quantitative cytoarchitectonic analysis revealed that somatosensory tDCS bilaterally increases cortical neural density. The findings emphasize the central role of bilateral somatosensory feedback in skill acquisition through modulation of cortico-motor excitability.

Functional connectivity‐based parcellation of amygdala using self‐organized mapping: A data driven approach

The overall goal of this work is to demonstrate how resting state functional magnetic resonance imaging (fMRI) signals may be used to objectively parcellate functionally heterogeneous subregions of the human amygdala into structures characterized by similar patterns of functional connectivity. We hypothesize that similarity of functional connectivity of subregions with other parts of the brain can be a potential basis to segment and cluster voxels using data driven approaches. In this work, self-organizing map (SOM) was implemented to cluster the connectivity maps associated with each voxel of the human amygdala, thereby defining distinct subregions. The functional separation was optimized by evaluating the overall differences in functional connectivity between the subregions at group level. Analysis of 25 resting state fMRI data sets suggests that SOM can successfully identify functionally independent nuclei based on differences in their inter subregional functional connectivity, evaluated statistically at various confidence levels. Although amygdala contains several nuclei whose distinct roles are implicated in various functions, our objective approach discerns at least two functionally distinct volumes comparable to previous parcellation results obtained using probabilistic tractography and cytoarchitectonic analysis. Association of these nuclei with various known functions and a quantitative evaluation of their differences in overall functional connectivity with lateral orbital frontal cortex and temporal pole confirms the functional diversity of amygdala. The data driven approach adopted here may be used as a powerful indicator of structure-function relationships in the amygdala and other functionally heterogeneous structures as well.

The myeloarchitectonic studies on the human cerebral cortex of the Vogt–Vogt school, and their significance for the interpretation of functional neuroimaging data

The human cerebral cortex contains numerous myelinated fibres, many of which are concentrated in tangentially organized layers and radially oriented bundles. The spatial organization of these fibres is by no means homogeneous throughout the cortex. Local differences in the thickness and compactness of the fibre layers, and in the length and strength of the radial bundles renders it possible to recognize areas with a different myeloarchitecture. The neuroanatomical subdiscipline aimed at the identification and delineation of such areas is known as myeloarchitectonics. There is another, closely related neuroanatomical subdiscipline, named cytoarchitectonics. The aims and scope of this subdiscipline are the same as those of myeloarchitectonics, viz. parcellation. However, this subdiscipline focuses, as its name implies, on the size, shape and arrangement of the neuronal cell bodies in the cortex, rather than on the myelinated fibres. At the beginning of the twentieth century, two young investigators, Oskar and Cécile Vogt founded a centre for brain research, aimed to be devoted to the study of the (cyto+myelo) architecture of the cerebral cortex. The study of the cytoarchitecture was entrusted to their collaborator Korbinian Brodmann, who gained great fame with the creation of a cytoarchitectonic map of the human cerebral cortex. Here, we focus on the myeloarchitectonic studies on the cerebral cortex of the Vogt-Vogt school, because these studies are nearly forgotten in the present attempts to localize functional activations and to interprete findings in modern neuroimaging studies. Following introductory sections on the principles of myeloarchitectonics, and on the achievements of three myeloarchitectonic pioneers who did not belong to the Vogt-Vogt school, the pertinent literature is reviewed in some detail. These studies allow the conclusion that the human neocortex contains about 185 myeloarchitectonic areas, 70 frontal, 6 insular, 30 parietal, 19 occipital, and 60 temporal. It is emphasized that the data available, render it possible to compose a myeloarchitectonic map of the human neocortex, which is at least as reliable as any of the classic architectonic maps. During the realization of their myeloarchitectonic research program, in which numerous able collaborators were involved, the Vogts gradually developed a general concept of the organization of the cerebral cortex. The essence of this concept is that this structure is composed of about 200 distinct, juxtaposed 'Rindenfelder' or 'topistische Einheiten', which represent fundamental structural as well as functional entities. The second main part of this article is devoted to a discussion and evaluation of this 'Vogt-Vogt concept'. It is concluded that there is converging quantitative cytoarchitectonic, receptor architectonic, myeloarchitectonic, hodological, and functional evidence, indicating that this concept is essentially correct. The third, and final part of this article deals with the problem of relating particular cortical functions, as determined with neuroimaging techniques, to particular cortical structures. At present, these 'translation' operations are generally based on adapted, three-dimensional versions of Brodmann's famous map. However, it has become increasingly clear that these maps do not provide the neuroanatomical precision to match the considerable degree of functional segregation, suggested by neuroimaging studies. Therefore, we strongly recommend an attempt at combining and synthesizing the results of Brodmann's cytoarchitectonic analysis, with those of the detailed myeloarchitectonic studies of the Vogt-Vogt school. These studies may also be of interest for the interpretation of the myeloarchitectonic features, visualized in modern in vivo mappings of the human cortex.

Cortical Connections of Area V6Av in the Macaque: A Visual-Input Node to the Eye/Hand Coordination System

The goal of the present study was to elucidate the corticocortical afferent connections of area V6Av, the ventral subregion of area V6A, using retrograde neuronal tracers combined with physiological and cytoarchitectonic analyses in the macaque monkey. The results revealed that V6Av receives many of its afferents from extrastriate area V6, and from regions of areas V2, V3, and V4 subserving peripheral vision. Additional extrastriate visual projections originate in dorsal stream areas MT and MST. Area V6Av does not receive projections directly from V1; such connections were only observed when the injection sites crossed into area V6. The strongest parietal lobe afferents originate in fields V6Ad, PGm, MIP (medial intraparaietal), and PG, with frontal lobe afferents originating from the frontal eye field, caudal area 46, and the rostral subdivision of the dorsal premotor area (F7). A comparison of their respective connections supports the view that V6Av is functionally distinct from adjacent areas (V6 and V6Ad). The strong afferents from V6 and other extrastriate areas are consistent with physiological data that suggest that V6Av is primarily a visual area, supporting the notion that V6Av is part of a dorsomedial cortical network performing fast form and motion analyses needed for the visual guidance of action.

Functional localization within the prefrontal cortex: missing the forest for the trees?

Anatomical and functional studies of the prefrontal cortex (PFC) have identified multiple PFC subregions. We argue that the PFC is involved in cognitive functions exceeding the sum of specific functions attributed to its subregions. These can be revealed either by lesions of the whole PFC, or more specifically by selective disconnection of the PFC from certain types of information (for example, visual) allowing the investigation of PFC function in toto. Recent studies in macaque monkeys using the latter approach lead to a second conclusion: that the PFC, as a whole, could be fundamentally specialized for representing events that are extended in time. The representation of temporally complex events might underlie PFC involvement in general intelligence, decision-making, and executive function.

Probabilistic Maps, Morphometry, and Variability of Cytoarchitectonic Areas in the Human Superior Parietal Cortex

Recently, 8 areas (5Ci, 5M, 5L, 7PC, 7A, 7P, 7M, hIP3) in the human superior parietal cortex (SPC) were delineated in 10 postmortem brains using observer-independent cytoarchitectonic analysis. Here we present 3D probabilistic maps of these areas, quantifying the interindividual overlap for each voxel in stereotaxic reference space, and a maximum probability map, providing a contiguous parcellation. For all areas, we determined probabilities of mutual borders, calculated stereotaxic centers of gravity, and estimated volumes. A basic pattern of areas and borders was observed, which showed, however, intersubject variations and a significant interhemispheric asymmetry (7P, 7M) that may be functionally relevant. There was a trend toward higher intersubject anatomical variability in lateral compared with medial areas. For several areas (5M, 7PC, 7A, 7P), variability was significantly higher in the left hemisphere and/or in men, whereas for areas 5Ci and 5M there was a hemisphere-by-gender interaction. Differences in anatomical variability could bias group analyses in functional imaging studies by reducing sensitivity for activations of entities with high variability. The probabilistic maps provide an objective anatomical reference and account for the structural variability of the human brain. Integrated into functional imaging experiments, they can improve structure-function investigations of the human SPC.