Quantitative cytoarchitectonics of the posterior cingulate cortex in primates

Precuneus brain response changes differently during human-robot and human-human dyadic social interaction

Human–human interactions (HHI) and human–robot interactions (HRI) are compared to identify differences between cognitive processes reflecting bonding in social interactions with natural and artificial agents. We capitalize on a unique corpus of neuroimaging data (fMRI) recorded while participants freely discussed with another human or a conversational robotic head, in order to study a crucial parameter of human social cognition, namely that social interactions are adaptive bidirectional processes that evolve over time. We used linear statistics to identify regions of the brain where activity changes differently when participants carry out twelve one-minute conversations, alternating between a human and a robotic interlocutor. Results show that activity in the posterior cingulate cortex, a key region associated with social cognition, increases over time in HHI but not in HRI. These results are interpreted as reflecting a process of strengthening social bonding during repeated exchanges when the interacting agent is a human, but not a robot.

A structural and functional subdivision in central orbitofrontal cortex

Economic choice requires many cognitive subprocesses, including stimulus detection, valuation, motor output, and outcome monitoring; many of these subprocesses are associated with the central orbitofrontal cortex (cOFC). Prior work has largely assumed that the cOFC is a single region with a single function. Here, we challenge that unified view with convergent anatomical and physiological results from rhesus macaques. Anatomically, we show that the cOFC can be subdivided according to its much stronger (medial) or weaker (lateral) bidirectional anatomical connectivity with the posterior cingulate cortex (PCC). We call these subregions cOFCm and cOFCl, respectively. These two subregions have notable functional differences. Specifically, cOFCm shows enhanced functional connectivity with PCC, as indicated by both spike-field coherence and mutual information. The cOFCm-PCC circuit, but not the cOFCl-PCC circuit, shows signatures of relaying choice signals from a non-spatial comparison framework to a spatially framed organization and shows a putative bidirectional mutually excitatory pattern.

Critique of Pure Marmoset

The common marmoset, a New World (platyrrhine) monkey, is currently being fast-tracked as a non-human primate model species, especially for genetic modification but also as a general-purpose model for research on the brain and behavior bearing on the human condition. Compared to the currently dominant primate model, the catarrhine macaque monkey, marmosets are notable for certain evolutionary specializations, including their propensity for twin births, their very small size (a result of phyletic dwarfism), and features related to their small size (rapid development and relatively short lifespan), which result in these animals yielding experimental results more rapidly and at lower cost. Macaques, however, have their own advantages. Importantly, macaques are more closely related to humans (which are also catarrhine primates) than are marmosets, sharing approximately 20 million more years of common descent, and are demonstrably more similar to humans in a variety of genomic, molecular, and neurobiological characteristics. Furthermore, the very specializations of marmosets that make them attractive as experimental subjects, such as their rapid development and short lifespan, are ways in which marmosets differ from humans and in which macaques more closely resemble humans. These facts warrant careful consideration of the trade-offs between convenience and cost, on the one hand, and biological realism, on the other, in choosing between non-human primate models of human biology. Notwithstanding the advantages marmosets offer as models, prudence requires continued commitment to research on macaques and other primate species.

Cellular signatures in the primary visual cortex of phylogeny and placentation

The long-held view that brain size can be used as an index of general functional capacity across mammals is in conflict with increasing evidence for phyletic differences in cellular organization. Furthermore, it is poorly understood how the internal cellular organization of the brain covaries with overall brain size variation. Using design-based stereology, we quantified glial cell and neuronal densities in the primary visual cortex of 71 mammalian species (spanning 11 orders) to test how those cellular densities are influenced by phylogeny, behavior, environment, and anatomy. We further tested cellular densities against mode of placentation to determine whether a relationship may exist. We provide evidence for cellular signatures of phylogenetic divergence from the mammalian trend in primates and carnivores, as well as considerably divergent scaling patterns between the primate suborders, Strepsirrhini and Haplorrhini, that likely originated at the anthropoid stem. Finally, we show that cellular densities in the mammalian cortex relate to the variability of maternal resources to the fetus in a species.

Spatial organization of neurons in the frontal pole sets humans apart from great apes

Few morphological differences have been identified so far that distinguish the human brain from the brains of our closest relatives, the apes. Comparative analyses of the spatial organization of cortical neurons, including minicolumns, can aid our understanding of the functionally relevant aspects of microcircuitry. We measured horizontal spacing distance and gray-level ratio in layer III of 4 regions of human and ape cortex in all 6 living hominoid species: frontal pole (Brodmann area [BA] 10), and primary motor (BA 4), primary somatosensory (BA 3), and primary visual cortex (BA 17). Our results identified significant differences between humans and apes in the frontal pole (BA 10). Within the human brain, there were also significant differences between the frontal pole and 2 of the 3 regions studied (BA 3 and BA 17). Differences between BA 10 and BA 4 were present but did not reach significance. These findings in combination with earlier findings on BA 44 and BA 45 suggest that human brain evolution was likely characterized by an increase in the number and width of minicolumns and the space available for interconnectivity between neurons in the frontal lobe, especially the prefrontal cortex.

Implications of the “initial brain” concept for brain evolution in Cetacea

We review the evidence for the concept of the “initial” or prototype brain. We outline four possible modes of brain evolution suggested by our new findings on the evolutionary status of the dolphin brain. The four modes involve various forms of deviation from and conformity to the hypothesized initial brain type. These include examples of conservative evolution, progressive evolution, and combinations of the two in which features of one or the other become dominant. The four types of neocortical organization in extant mammals may be the result of selective pressures on sensory/motor systems resulting in divergent patterns of brain phylogenesis. A modular “modification/multiplication” hypothesis is proposed as a mechanism of neocortical evolution in eutherians. Representative models of the initial ancestral group of mammals include not only extant basal Insectivora but also Chiroptera; we have found that dolphins and large whales have also retained many features of the archetypal or initial brain. This group evolved from the initial mammalian stock and returned to the aquatic environment some 50 million years ago. This unique experiment of nature shows the effects of radical changes in environment on brain-body adaptations and specializations. Although the dolphin brain has certain quantitative characteristics of the evolutionary changes seen in the higher terrestrial mammals, it has also retained many of the conservative structural features of the initial brain. Its neocortical organization is accordingly different, largely in a quantitative sense, from that of terrestrial models of the initial brain such as the hedgehog.

Neurite density from magnetic resonance diffusion measurements at ultrahigh field: comparison with light microscopy and electron microscopy

Due to its unique sensitivity to tissue microstructure, diffusion-weighted magnetic resonance imaging (MRI) has found many applications in clinical and fundamental science. With few exceptions, a more precise correspondence between physiological or biophysical properties and the obtained diffusion parameters remain uncertain due to lack of specificity. In this work, we address this problem by comparing diffusion parameters of a recently introduced model for water diffusion in brain matter to light microscopy and quantitative electron microscopy. Specifically, we compare diffusion model predictions of neurite density in rats to optical myelin staining intensity and stereological estimation of neurite volume fraction using electron microscopy. We find that the diffusion model describes data better and that its parameters show stronger correlation with optical and electron microscopy, and thus reflect myelinated neurite density better than the more frequently used diffusion tensor imaging (DTI) and cumulant expansion methods. Furthermore, the estimated neurite orientations capture dendritic architecture more faithfully than DTI diffusion ellipsoids.

Architectonic mapping of the medial region of the human orbitofrontal cortex by density profiles

The study of architectonic differentiation in the cortex is advanced by the articulation of objective definitions based on clear features of the cortical architecture. We adopted areal density profiles as a means of sampling the cortex. On the profiles, we isolated and quantified the density of individual cortical layers. These features may serve as criteria in objective definitions in a way that builds on qualitative observations found in the classical literature. A preprocessing procedure was introduced to overcome artefacts in the density profiles caused by the partial overlap of neighboring neuronal layers and cortical folding. We applied this method to the medial half of the orbital frontal cortex in specimens drawn from 10 human postmortem brain hemispheres. The measurements successfully confirmed the existence of several qualitatively observed areas (architectonic areas 14c, 14r, 11m, 11 and 13). The selection of specific sampling parameters was justified on the basis of simultaneous measurements of the cortical morphology which demonstrate its influence on the appearance of the cortical layers. We also examined the robustness of the measuring procedure by analyzing the outcome of varying systematically the sampling parameters. We describe here a novel method of sampling the cortex for architectonic analysis and demonstrate its application on histological sections obtained from the medial half of the human orbitofrontal cortex.

Modeling dendrite density from magnetic resonance diffusion measurements

Diffusion-weighted imaging (DWI) provides a noninvasive tool to probe tissue microstructure. We propose a simplified model of neural cytoarchitecture intended to capture the essential features important for water diffusion as measured by NMR. Two components contribute to the NMR signal in this model: (i) the dendrites and axons, which are modeled as long cylinders with two diffusion coefficients, parallel (D(L)) and perpendicular (D(T)) to the cylindrical axis, and (ii) an isotropic monoexponential diffusion component describing water diffusion within and across all other structures, i.e., in extracellular space and glia cells. The model parameters are estimated from 153 diffusion-weighted images acquired from a formalin-fixed baboon brain. A close correspondence between the data and the signal model is found, with the model parameters consistent with literature values. The model provides an estimate of dendrite density from noninvasive MR diffusion measurements, a parameter likely to be of value for understanding normal as well as abnormal brain development and function.

Cytoarchitectonic identification and probabilistic mapping of two distinct areas within the anterior ventral bank of the human intraparietal sulcus

Anatomical studies in the macaque cortex and functional imaging studies in humans have demonstrated the existence of different cortical areas within the intraparietal sulcus (IPS). Such functional segregation, however, does not correlate with presently available architectonic maps of the human brain. This is particularly true for the classical Brodmann map, which is still widely used as an anatomical reference in functional imaging studies. The aim of this cytoarchitectonic mapping study was to use previously defined algorithms to determine whether consistent regions and borders can be found within the cortex of the anterior IPS in a population of 10 post-mortem human brains. Two areas, the human intraparietal area 1 (hIP1) and the human intraparietal area 2 (hIP2), were delineated in serial histological sections of the anterior, lateral bank of the human IPS. The region hIP1 is located posterior and medial to hIP2, and the former is always within the depths of the IPS. The latter, on the other hand, sometimes reaches the free surface of the superior parietal lobule. The delineations were registered to standard reference space, and probabilistic maps were calculated, thereby quantifying the intersubject variability in location and extent of both areas. In the future, they can be a tool for analyzing structure-function relationships and a basis for determining degrees of homology in the IPS among anthropoid primates. We conclude that the human IPS has a more finely grained parcellation than shown in Brodmann's map.

Neuronal density and architecture (Gray Level Index) in the brains of autistic patients

Although neuropathologic studies have centered on small samples, it is accepted that brains of autistic individuals tend to be large, on average. Knowledge regarding the cause of this macrocephaly is limited. Postmortem studies reveal little in terms of cortical dysplasia. Some of these studies suggest increased cell-packing density in subcortical structures. These neuronomorphometric studies have been subjective or based their conclusions on measures of neuronal density. Our study sought the possible presence of increased cell-packing density by using the Gray Level Index. The Gray Level Index is defined as the ratio of the area covered by Nissl-stained elements to unstained area in postmortem samples. Analyzed images included Brodmann's cortical areas 9, 21, and 22 of 9 autistic patients (7 males, 2 females; mean age of 12 years, with a range of 5 to 28 years) and 11 normal controls (7 males, 4 females; mean age of 14 years, with a range of 3 to 25 years). The overall multivariate test revealed significant differences both between autistic patients and controls (P = .001) and between hemispheres (P = .025). Follow-up univariate tests showed significant diagnosis-dependent effects in feature distance (P = .005), the standard deviation in distance (P = .016), and feature amplitude (P = .001). The overall mean Gray Level Index was 19.4% in controls and 18.7% in autism (P = .724). In autism, an increased number of minicolumns, combined with fewer cells per column (or their greater dispersion), results in no global difference in neuronal density.

The minicolumn hypothesis in neuroscience

The minicolumn is a continuing source of research and debate more than half a century after it was identified as a component of brain organization. The minicolumn is a sophisticated local network that contains within it the elements for redundancy and plasticity. Although it is sometimes compared to subcortical nuclei, the design of the minicolumn is a distinctive form of module that has evolved specifically in the neocortex. It unites the horizontal and vertical components of cortex within the same cortical space. Minicolumns are often considered highly repetitive, even clone-like, units. However, they display considerable heterogeneity between areas and species, perhaps even within a given macrocolumn. Despite a growing recognition of the anatomical basis of the cortical minicolumn, as well as its physiological properties, the potential of the minicolumn has not been exploited in fields such as comparative neuroanatomy, abnormalities of the brain and mind, and evolution.

Macaque monkey retrosplenial cortex: I. three-dimensional and cytoarchitectonic organization

This is the first in a series of reports on the neuroanatomic organization and connectivity of the macaque monkey retrosplenial cortex, i.e., areas 29 and 30. To elucidate the topographic configuration of the retrosplenial cortex and adjacent structures, we have made three-dimensional computer reconstructions of the posterior cingulate region that includes the retrosplenial cortex. The largest portion of the posterior cingulate gyrus is located dorsal to the corpus callosum. At the caudal limit of the corpus callosum, the gyrus curves around the splenium, turns laterally and forms a region called the isthmus that links the cingulate and parahippocampal gyri. The isthmus contains the caudomedial lobule, which is a rostrally oriented bulge that is made up, in part, of portions of the retrosplenial cortex. To delineate the subdivisions of the retrosplenial and adjacent cortices, we conducted a cytoarchitectonic analysis by using cerebral hemispheres that were cut at oblique angles and stained with a variety of techniques, including immunohistochemistry for nonphosphorylated neurofilament protein. The dorsal bank of the callosal sulcus and the rostral surface of the isthmus are covered by the retrosplenial cortical areas 29l, 29m, and 30, whereas most of the medial surface of the posterior cingulate gyrus and the ventral bank of the posterior cingulate sulcus consist of areas 23i and 23e. The most caudoventral portion of the cingulate gyrus is composed of an area (area 23v) that resembles the retrosplenial and posterior cingulate cortices but has a much more prominent layer IV. On the dorsal bank of the calcarine sulcus, we also defined a transitional zone, area 30v, located between the retrosplenial cortex and the prestriate visual cortex.

Architectonic analysis of the human retrosplenial cortex

The architecture of the macaque retrosplenial cortex, including its posteroventral extension around and below the splenium of the corpus callosum, was recently characterized (Morris et al. [1999a] Eur. J. Neurosci. 11:2506-2518.). This analysis was made possible by sectioning the posterior cingulate gyrus radially, i.e., in planes that were orthogonal to its line of curvature and that, therefore, preserved the laminar organization of this region. The aim of the present study was to examine the architecture and the limits of the human retrosplenial cortex. Cross sections through the entire posterior cingulate gyrus were obtained by applying the sectioning technique developed in the monkey, so that an explicit comparison could be made between the architecture of the human and the monkey retrosplenial cortex. The present analysis revealed that, as is the case in the macaque brain, the human retrosplenial cortex is composed of granular areas 29a-c and d, and dysgranular/agranular area 30. The human retrosplenial cortex, like that of the macaque monkey, runs, as an arch, around the splenium of the corpus callosum. In the macaque brain, the retrosplenial cortex remains buried within the callosal sulcus throughout its entire course around the splenium. In the human brain, however, the posteroventral segment of the retrosplenial cortex extends on the medial wall of the cerebral hemisphere to encompass most of the cortical region commonly referred to as the "isthmus of the cingulate gyrus."

Brodmann's areas 17 and 18 brought into stereotaxic space-where and how variable?

Studies on structural-functional associations in the visual system require precise information on the location and variability of Brodmann's areas 17 and 18. Usually, these studies are based on the Talairach atlas, which does not rely on cytoarchitectonic observations, but on comparisons of macroscopic features in the Talairach brain and Brodmann's drawing. In addition, in this atlas are found only the approximate positions of cytoarchitectonic areas and not the exact borders. We have cytoarchitectonically mapped both areas in 10 human brains and marked their borders in corresponding computerized images. Borders were defined on the basis of quantitative cytoarchitecture and multivariate statistics. In addition to borders of areas 17 and 18, subparcellations within both areas were found. The cytoarchitectonically defined areas were 3-D reconstructed and transferred into the stereotaxic space of the standard reference brain. Surface rendering of the brains revealed high individual variability in size and shape of the areas and in the relationship to the free surface and sulci. Ranges and centers of gravity of both areas were calculated in Talairach coordinates. The positions of areas 17 and 18 in the stereotaxic space differed between the hemispheres. Both areas reached significantly more caudal and medial positions on the left than on the right. Probability maps were created in which the degree of overlap in each stereotaxic position was quantified. These maps of areas 17 and 18 are the first of their kind and contain precise stereotaxic information on both interhemispheric and interindividual differences.

Broca's region revisited: cytoarchitecture and intersubject variability

The sizes of Brodmann's areas 44 and 45 (Broca's speech region) and their extent in relation to macroscopic landmarks and surrounding areas differ considerably among the available cytoarchitectonic maps. Such variability may be due to intersubject differences in anatomy, observer-dependent discrepancies in cytoarchitectonic mapping, or both. Because a reliable definition of cytoarchitectonic borders is important for interpreting functional imaging data, we mapped areas 44 and 45 by means of an observer-independent technique. In 10 human brains, the laminar distributions of cell densities were measured vertical to the cortical surface in serial coronal sections stained for perikarya. Thousands of density profiles were obtained. Cytoarchitectonic borders were defined as statistically significant changes in laminar patterns. The analysis of the three-dimensional reconstructed brains and the two areas showed that cytoarchitectonic borders did not consistently coincide with sulcal contours. Therefore, macroscopic features are not reliable landmarks of cytoarchitectonic borders. Intersubject variability in the cytoarchitecture of areas 44 and 45 was significantly greater than cytoarchitectonic differences between these areas in individual brains. Although the volumes of area 44 differed across subjects by up to a factor of 10, area 44 but not area 45 was left-over-right asymmetrical in all brains. All five male but only three of five female brains had significantly higher cell densities on the left than on the right side. Such hemispheric and gender differences were not detected in area 45. These morphologic asymmetries of area 44 provide a putative correlate of the functional lateralization of speech production.

Architecture and connections of retrosplenial area 30 in the rhesus monkey (Macaca mulatta)

Because of the sharp curvature of the retrosplenial region around the splenium of the corpus callosum, standard coronal sections are not appropriate for architectonic analysis of its posteroventral part. In the present study, examination of the posteroventral retrosplenial region of the rhesus monkey in sections that were orthogonal to its axis of curvature (and therefore appropriate for architectonic analysis) has permitted definition of its architecture and precise extent. This analysis demonstrated that areas 29 and 30 of the retrosplenial cortex, as well as adjacent area 23 of the posterior cingulate cortex, extend together as an arch around the splenium of the corpus callosum and maintain their topographical relationship with one another throughout their entire course. Injections of anterograde and retrograde tracers confined to retrosplenial area 30 revealed that this area has reciprocal connections with adjacent areas 23, 19 and PGm, with the mid-dorsolateral part of the prefrontal cortex (areas 9, 9/46 and 46), with multimodal area TPO in the superior temporal sulcus, as well as the posterior parahippocampal cortex, the presubiculum and the entorhinal cortex. There are also bidirectional connections with the lateroposterior thalamic nucleus, as well as the laterodorsal and the anteroventral limbic thalamic nuclei. The connectivity of area 30 suggests that it may play a role in working memory processes subserved by the mid-dorsolateral frontal cortex in interaction with the hippocampal system.

Limbic frontal cortex in hominoids: a comparative study of area 13

The limbic frontal cortex forms part of the neural substrate responsible for emotional reactions to social stimuli. Area 13 is one of the cortical areas long known to be part of the posterior orbitofrontal cortex in several monkey species, such as the macaque. Its presence nevertheless in the human brain has been unclear, and the cortex of the frontal lobe of the great and lesser apes remains largely unknown. In this study area 13 was identified in human, chimpanzee, bonobo, gorilla, orangutan, and gibbon brains, and cortical maps were generated on the basis of its cytoarchitecture. Imaging techniques were used to characterize and quantify the microstructural organization of the area, and stereological tools were applied for estimates of the volume of area 13 in all species. Area 13 is conservative in its structure, and features such as size of cortical layers, density of neurons, and space available for connections are similar across hominoids with only subtle differences present. In contrast to the homogeneity found in its organization, variation is present in the relative size of this cortical area (as a percentage of total brain volume). The human and the bonobo include a complex orbitofrontal cortex and a relatively smaller area 13. On the contrary the orangutan stands out by having a shorter orbitofrontal region and a more expanded area 13. Differences in the organization and size of individual cortical areas involved in emotional reactions and social behavior can be related to behavioral specializations of each hominoid and to the evolution of emotions in hominids.

Systematic investigations of the contrast results of histochemical stainings of neurons and glial cells in the human brain by means of image analysis

The investigation of neurohistological specimens by image analysis has become an important tool in morphological neuroscience. The problems which arise during the processing of these images are non-trivial, especially if a pattern recognition of cells in the imaged tissue is intended. One of the major problems faced concerns the segmentation of structures of interest, whether cells or other histologic structures. The segmentation problem is often the result of an inappropriate staining procedure. For serious image analysis to be performed, the material under investigation must be optimally prepared. Spatially complex patterns, e.g. fuzzy-like neighbouring neurons, are easy to recognize for humans. But the integrative and associative performance of current artificial neuronal network schemes is too low to achieve the same recognition quality as humans do. Therefore, a general analysis of staining characteristics was performed, especially with respect to those stains which are relevant to object segmentation. Although most image analytical investigations of tissues are based on stained samples, a study of this type has not been previously conducted. Of the stains and procedures evaluated, the gallocyanin chrome alum combination staining provided the best stain contrast. Furthermore, this staining method shows sufficient constancy within different parts of the human brain. Even the fine nuclear textures are differentiable and can be used for further pattern recognition procedures.

Postmortem cryosectioning as an anatomic reference for human brain mapping

This study examined the densitometric and topographic detail of high resolution 3D digital postmortem cryosectioned brain images. Anatomic image data and histology from cryosectioned human brain were compared to in vivo MRI for the ability to delineate neuroanatomic structure. 3D surface reconstructions in the Talairach and Tournoux atlas ("Co-planar stereotaxic atlas of the human brain", Thieme, New York, 1988) coordinate system enabled morphometric comparisons for a representative sample of neuroanatomic structures. Spatial resolution of cryosection images averaged 200 and 170 microns/pixel for whole head and brain, respectively, and 40 microns/pixel for isolated the brain regions. Anatomic detail was far superior to MRI, particularly in deep subcortical regions such as the basal ganglia and in mesencephalic nuclei and tracts. Digital repositioning in the Talairach coordinate system enabled efficient structure localization and morphometric comparison. Histology from collected tissue sections provided cytologic detail that could be mapped to its approximate 3D context. This approach permits comprehensive morphometric analyses necessary for an anatomic framework to a digital atlas of the human brain.

Human cingulate cortex: surface features, flat maps, and cytoarchitecture

The surface morphology and cytoarchitecture of human cingulate cortex was evaluated in the brains of 27 neurologically intact individuals. Variations in surface features included a single cingulate sulcus (CS) with or without segmentation or double parallel sulci with or without segmentation. The single CS was deeper (9.7 +/- 0.81 mm) than in cases with double parallel sulci (7.5 +/- 0.48 mm). There were dimples parallel to the CS in anterior cingulate cortex (ACC) and anastomoses between the CS and the superior CS. Flat maps of the medial cortical surface were made in a two-stage reconstruction process and used to plot areas. The ACC is agranular and has a prominent layer V. Areas 33 and 25 have poor laminar differentiation, and there are three parts of area 24: area 24a adjacent to area 33 and partially within the callosal sulcus has homogeneous layers II and III, area 24b on the gyral surface has the most prominent layer Va of any cingulate area and distinct layers IIIa-b and IIIc, and area 24c in the ventral bank of the CS has thin layers II-III and no differentiation of layer V. There are four caudal divisions of area 24. Areas 24a' and 24b' have a thinner layer Va and layer III is thicker and less dense than in areas 24a and 24b. Area 24c' is caudal to area 24c and has densely packed, large pyramids throughout layer V. Area 24c' g is caudal to area 24c' and has the largest layer Vb pyramidal neurons in cingulate cortex. Area 32 is a cingulofrontal transition cortex with large layer IIIc pyramidal neurons and a dysgranular layer IV. Area 32' is caudal to area 32 and has an indistinct layer IV, larger layer IIIc pyramids, and fewer neurons in layer Va. Posterior cingulate cortex has medial and lateral parts of area 29, a dysgranular area 30, and three divisions of area 23: area 23a has a thin layer IIIc and moderate-sized pyramids in layer Va, area 23b has large and prominent pyramids in layers IIIc and Va, and area 23c has the thinnest layers V and VI in cingulate cortex. Area 31 is the cinguloparietal transition area in the parasplenial lobules and has very large layer IIIc pyramids. Finally, variations in architecture between cases were assessed in neuron perikarya counts in area 23a. There was an age-related decrease in neuron density in layer IV (r = -0.63; ages 45-102), but not in other layers.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitative analysis of the columnar arrangement of neurons in the human cingulate cortex

The spatial organization of human cingulate (areas 24b, 23b, and 31) and pericingulate (areas 7 and 19) cortex was examined by using an image analyzer to measure characteristics of vertically oriented, translaminar columns of neurons in the cerebral cortex. Columns of 30-50 microns in diameter are hypothesized to be a general feature of cortical organization, but no quantitative analysis of different human cortical areas has been performed. Our results prove for the first time that a columnar organization was detectable in every area examined. The average width of cell columns was approximately 40 microns separated by a neuropil-rich fascicle of the same dimension. Because differences in the expression of a columnar organization were seen, the degree of columnization was subsequently expressed by a verticality index (VI) revealing specific changes in its dimension depending on the architectonic area. The VI was calculated by a linear combination of three variables derived from the measurement of cell density profiles in Nissl-stained sections at right angles to vertically oriented cell columns. Variables included the amplitude of profile peaks, the standard deviation of the width of those profile peaks, and the standard deviation of the distances between profile peaks. The index of verticality describes the deviation of a distinct area and layer from the mean degree of vertical organization of all cortical areas and layers examined. Thus, different degrees of columnar organization can be quantitatively described by the verticality index and can be used as criteria to characterize architectonic areas.

Brain atlases--a new research tool

Conventional brain atlases are collections of micrographs or schematic drawings of brain sections from one or a few brains in which anatomical structures are identified, for example, nuclei, cortical areas and fibre tracts. Conventional brain maps have now been replaced with modern computer-based brain atlases. The structures in computerized atlases are deformable so as to fit the sizes and shapes of individual brains, and transform three-dimensional reconstructions or images of brains into a standard brain format. In order to make generalizations about localization of function and structure at both the macroscopical and microscopical level computerized brain atlases are needed. Computerized brain atlases are also used to compensate for the shrinkage and distortions during sectioning and embedding of post-mortem brains, to study structural-functional relationships in the human brain at both the macroscopical and microscopical level, and variations in gross morphology and microstructure of the human brain, and for establishing a three-dimensional human-brain database for all of the above and also for topographically defined data from the literature.

Layer V pyramidal cells in the adult human cingulate cortex. A quantitative Golgi-study

The anterior and posterior parts of the human cingulate cortex differ in their absolute number of neurons per unit volume, with fewer neurons in the anterior part. To test the hypothesis that lower absolute number and packing density of neurons in the anterior cingulate cortex are associated with an increased complexity in the neuropil compartment, dendritic arborizations of layer V neurons in both cingulate parts were analyzed in a Golgi study. Results show that these neurons in the anterior cingulate cortex have more primary and secondary basal dendrites than those in the posterior cingulate cortex. This establishes an association of a higher complexity of the dendritic arborization in the anterior cingulate cortex with a lower cell number per unit volume and larger neuropil compartment. The significant lower degree of dendritic arborization in the posterior cingulate cortex is accompanied by a higher cell packing density. These structural differences are associated with functional differences between the two parts of the human cingulate cortex.

Architectonics of the parietal and temporal association cortex in the strepsirhine primate Galago compared to the anthropoid primate Macaca

A number of higher order association areas have been described in the parietal and temporal cortex of large-brained anthropoid primates such as Macaca. However, little is known about the evolution of these areas, and the existence of homologous areas has not yet been clearly demonstrated in other mammalian groups. We addressed this issue by comparing the myelo- and cytoarchitecture of posterior association cortex in the anthropoid Macaca to that of the small-brained, strepsirhine ("prosimian") primate Galago. Our results suggest that Galago possesses many, if not most, of the areas present in Macaca. We were able to identify regions in Galago which resemble Macaca posterior parietal area 7, superior temporal polysensory cortex (ST), inferotemporal visual cortex (IT), the temporoparietal auditory area (Tpt), and posterior parahippocampal cortex (areas TH and TF). Area 7, ST, and IT can each be subdivided further in Macaca, and for most of these subdivisions we were able to identify counterparts in Galago. However, we could not distinguish as many divisions of ST cortex in Galago as in Macaca, and it is possible that new areas arose in this region during anthropoid evolution. There also appear to be general differences in architectonic organization between these animals, with Macaca exhibiting greater development of pyramidal layer IIIc and of the internal granular layer (IV) across much of the parieto-temporal cortex. These findings suggest that many, although possibly not all, of the parietal and temporal association areas present in the modern anthropoid Macaca evolved early in primate history, prior to the divergence of the lineages leading to strepsirhines and anthropoids.

Laminar distribution of neuron degeneration in posterior cingulate cortex in Alzheimer's disease

The laminar distribution of neuron losses in posterior cingulate cortex were evaluated in 25 clinically and neuropathologically diagnosed cases of dementia of the Alzheimer type (DAT). The layer of maximal neuron loss in area 23a for each DAT case was determined by comparison with mean neuron densities for each layer of 17 neurologically intact control cases. The DAT cases were separated into five classes: class 1, 12% of all DAT cases, no or less than 40% neuron loss in any layer; class 2, 24%, maximal neuron losses in layers II or III; class 3, 28%, losses mainly in layer IV; class 4, 12%, losses mainly in layers V or VI; class 5, 24%, severe losses in all layers. An analysis of large and small neurons showed that in class 2 there was an equal loss of both in layer IIIa--b, in class 3 mostly small neurons were lost in layer IV, in class 4 mostly large neurons were lost in layers III, IV and V, while in class 5 there was no selectivity. The age of disease onset and length of the disease were the same for all classes, although classes 4 and 5 tended to have an earlier onset. No measures of thioflavin S-stained neuritic plaque (NP) or neurofibrillary tangle (NFT) density discriminated among these classes. In 64% of all DAT cases there was a progressive shift in NFT from ventral area 30 where most were in layer II to areas 23a--b where there was a balance between those in superficial and deep layers to dorsal area 23c where most were in layers V and VI.(ABSTRACT TRUNCATED AT 250 WORDS)

A quantitative approach to cytoarchitectonics: analysis of structural inhomogeneities in nervous tissue using an image analyser

Cytoarchitectonic investigations are based on the analysis of structural inhomogeneities in the neuronal composition of nervous tissue. Boundaries of brain regions are established at locations where local structural properties, such as density, shape, orientation or arrangement of the nerve cells, change. A quantitative approach requires a complete scanning of histological sections and the measurement of at least one of these properties using an automatic device. In contrast to recently developed stereological methods which result in unbiased estimates of parameters and which are based on efficient sampling procedures, measurements with automatic devices are biased due to section thickness and problems in the segmentation of nerve cell bodies. Automatic measurements are necessary, however, if a complete scanning of histological sections is required in order to localize areal or laminar boundaries. In this approach, the grey level index (GLI) is measured with a TV-based image analysing system from routine histological sections. Using Nissl-staining, this parameter is a biased estimate of the local volume density of Nissl-positive structures (cell bodies). The histological section is digitized into a GLI image by a scanning procedure. The GLI image is processed by image enhancement procedures in order to visualize the laminar pattern. Areal boundaries are localized at positions where this laminar pattern changes. GLI statistics of single brain regions can easily be evaluated by delineating these regions with a cursor in the GLI images of the sections. Information from a series of sections is compiled by specific application programs.

Laminar distributions of muscarinic acetylcholine, serotonin, GABA and opioid receptors in human posterior cingulate cortex

Experimental animal studies have demonstrated a number of receptor localizations on specific cortical afferents and neurons. The present study of human posterior cingulate cortex evaluates the laminar distributions of particular receptors and their likely association with components of the neuropil. Coverslip autoradiographic and single grain counting techniques were used followed by heterogeneity analysis in which the layer of peak binding and an index of heterogeneity were determined for each ligand. The index was calculated by determining specific binding by layer as a percentage of binding in all layers. The differences from an absolutely homogeneous distribution, i.e. 11.1% for each of nine layers, were subtracted and the absolute laminar differences summed to form the index. High indices of over 15 reflected heterogeneous binding patterns in neocortex. The binding of ligands for muscarinic acetylcholine, serotonin, opioid, GABA and beta adrenoceptors was evaluated. Pirenzepine binding peaked in layer II of area 23a but was extremely homogeneous with an index of heterogeneity of 8.9. In contrast, oxotremorine-M binding had a peak in layer IIIc and an index of 16.4, while AF-DX 116 binding peaked in layer IIIa-b and had an index of 30.6. Of the ligands for serotonin uptake and receptor binding paroxetine binding was evenly distributed in layers I-III and had a low index of heterogeneity of 9.8. Ketanserin binding was also homogeneous and, since it had an index of 8.9, this pattern was virtually the same as that for paroxetine. In contrast, serotonin and 8-hydroxy-2-(di-n-propylamino)tetralin binding peaked in layer II and had very high indices of 20.8 and 50.3, respectively, suggesting only a limited association with that of the paroxetine distribution. Finally, there were three layers which contained peaks in binding for ligands for opioid, GABA and beta adrenoceptors. Firstly, layer Ia had peak dynorphin-A binding, the latter of which had an index of 22.6. Secondly, Tyr-D-Ala-Gly-MePhe-Gly-ol and 2-D-penicillamine-5-D-penicillamine-enkephalin binding peaked in layer II and had indices of 8.6 and 17.4, respectively. Thirdly, muscimol and (-)-cyanopindolol binding peaked in layer IIIa-b and had indices of 29.6 and 11.1, respectively. When viewed in the context of experimental animal studies, it is likely that heterogeneities in oxotremorine-M and paroxetine binding are associated with the termination of the thalamic and raphe nuclei, respectively. While serotonin 2 receptors are co-distributed with serotonin uptake sites, serotonin 1A receptors have a significant mismatch with these sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Mode of [14C] 2-deoxy-D-glucose uptake into retrosplenial cortex and other memory-related structures of the monkey during a delayed response

Physiological studies on the monkey retrosplenial (RS) cortex have been few, and its functional role remains to be investigated. In the present study, activity of the RS cortex was investigated using radioactive 2-DG while the monkey was performing a visual tracking task with a delay (a delayed-response task) for 45 minutes. A remarkable increase in 2-DG uptake was observed equally in the left as well as in the right RS cortex. The anterior nucleus of the thalamus also showed increased 2-DG uptake. In addition, other memory-related structures (prefrontal cortex, dorsomedial nucleus of the thalamus, amygdala and hippocampus) showed a similar increase in 2-DG uptake compared to control monkeys, though their respective absolute values were different from one another. Since the RS cortex receives afferents from the anterior nucleus of the thalamus, which is one of the main nuclei of the Papez circuit, it is assumed that the RS cortex is important in memory function. Therefore, the remarkable increase in 2-DG uptake in the present study could reflect some aspects of memory or learning processes required to perform the delayed response.

The human pattern of gyrification in the cerebral cortex

The degree of cortical folding found in adult human brains has been analyzed using a gyrification index (GI). This parameter permits the description of a mean value for the whole brain, but also a local specific analysis of different brain regions. Correlation analyses of the GI with age, body weight, body length, brain weight and volume of the prosencephalon and the cortex show no significant results. GI values do not differ significantly between male and female brains, right and left hemispheres or right and left sides of the superior temporal plane. The GI shows maximal values over the prefrontal and the parieto-temporo-occipital association cortex. A comparison between the rostro-caudal GI patterns of human brains and those of prosimians and Old World monkeys shows the largest difference over the prefrontal cortex. The mean GI increases from prosimians to human brains with the highest values for non-human primates being in the pongid group.

Corticothalamic connections of paralimbic regions in the rhesus monkey

This study addressed the issue of whether paralimbic regions of the cerebral cortex share common thalamic projections. The corticothalamic connections of the paralimbic regions of the orbital frontal, medial prefrontal, cingulate, parahippocampal, and temporal polar cortices were studied with the autoradiographic method in the rhesus monkey. The results revealed that the orbital frontal, medial prefrontal, and temporal polar proisocortices have substantial projections to both the dorsomedial and medial pulvinar nuclei, whereas the anterior cingulate proisocortex (area 24) projects exclusively to the dorsomedial nucleus. These proisocortical areas also have thalamic connections with the intralaminar and midline nuclei. The cortical areas between the proisocortical regions on the one hand and the isocortical areas on the other, that is, the posterior cingulate region (area 23) and the posterior parahippocampal gyrus (areas TF and TH), project predominantly to the dorsal portion of the medial pulvinar nucleus, the anterior nuclear group (AV, AM), and the lateral dorsal (LD) nucleus. Additionally, the posterior cingulate and medial parahippocampal gyri (area TH) have projections to the lateral posterior (LP) nucleus. Thus, it appears that the proisocortical areas, which are characterized by a predominance of infragranular layers and an absence of layer IV, have common thalamic relationships. Likewise, the intermediate paralimbic areas between the proisocortex and isocortical regions, which also have a predominance of infragranular layers but in addition have evidence of a fourth layer, project to the medial pulvinar and to the so-called limbic nuclei, AV, AM, LD, as well as a modality-specific nucleus, LP.