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

Quantitative architectural analysis: a new approach to cortical mapping

Recent progress in anatomical and functional MRI has revived the demand for a reliable, topographic map of the human cerebral cortex. Till date, interpretations of specific activations found in functional imaging studies and their topographical analysis in a spatial reference system are, often, still based on classical architectonic maps. The most commonly used reference atlas is that of Brodmann and his successors, despite its severe inherent drawbacks. One obvious weakness in traditional, architectural mapping is the subjective nature of localising borders between cortical areas, by means of a purely visual, microscopical examination of histological specimens. To overcome this limitation, more objective, quantitative mapping procedures have been established in the past years. The quantification of the neocortical, laminar pattern by defining intensity line profiles across the cortical layers, has a long tradition. During the last years, this method has been extended to enable a reliable, reproducible mapping of the cortex based on image analysis and multivariate statistics. Methodological approaches to such algorithm-based, cortical mapping were published for various architectural modalities. In our contribution, principles of algorithm-based mapping are described for cyto- and receptorarchitecture. In a cytoarchitectural parcellation of the human auditory cortex, using a sliding window procedure, the classical areal pattern of the human superior temporal gyrus was modified by a replacing of Brodmann's areas 41, 42, 22 and parts of area 21, with a novel, more detailed map. An extension and optimisation of the sliding window procedure to the specific requirements of receptorarchitectonic mapping, is also described using the macaque central sulcus and adjacent superior parietal lobule as a second, biologically independent example. Algorithm-based mapping procedures, however, are not limited to these two architectural modalities, but can be applied to all images in which a laminar cortical pattern can be detected and quantified, e.g. myeloarchitectonic and in vivo high resolution MR imaging. Defining cortical borders, based on changes in cortical lamination in high resolution, in vivo structural MR images will result in a rapid increase of our knowledge on the structural parcellation of the human cerebral cortex.

Left-Right Asymmetry in Volume and Number of Neurons in Adult Broca's Area

Total neuron number in, and volume of, Brodmann areas (BA) 44 and 45 (Broca's area) were studied in Nissl-stained sections from the left and right hemispheres of five adult men and five adult women. The volume of BA 44 was greater in the left hemisphere than in the right in all ten cases, although asymmetry was only significant for the subgroup of male subjects. For six of the ten subjects (including all females), the volume of BA 45 was greater in the left hemisphere than the right. This asymmetry was significant only for the women. A significant left-over-right asymmetry has been found in total neuron number in male BA 44. Although the total number of neurons in left BA 45 was larger in all five female subjects, this asymmetry did not reach significant difference. In the male subjects no significant asymmetry difference in total neuron number was found in BA 45 either. There was no significant hemispheric asymmetry or gender interaction for neuronal number density, either in BA 44 or 45. This study is the first quantitative study of total number of neurons in BA 44 and 45 in adult subjects, and demonstrates that both the volume and the total neuron number of BA 44 and 45 on the left are generally greater than that of the right hemisphere, with the possible exception of the male BA 45. In addition, it shows that the inter-individual variability was also very large (more than twofold) in the numerical values of all variables.

The Anatomical Segregation of the Frontal Cortex: What Does it Mean for Function?

The frontal cortex consists of numerous areas, each with a special architecture (cyto-, myelo-, receptorarchitecture, etc.), connectivity and function. Quantitative tools of the analysis may assist in defining these cortical areas, and their position in a hierarchy of cortical regions and subregions. They enable a reliable definition of areal borders, and the consideration of intersubject variability. In our particular case, fMRI studies investigating certain aspects of cognitive control indicated to a rather circumscribed area in the posterior frontolateral cortex--the so-called IFJ area--which seems to correspond anatomically to a previously uncharted cortical area dorsally to area 44 as detected in histological sections of post mortem brains.

Intact hippocampal gray matter in schizophrenia as revealed by automatized image analysis postmortem

Implicated as a key structure in the pathophysiology of schizophrenia, the hippocampus is at the forefront of neuropathological and neuroimaging research. To elucidate the cellular basis of hippocampal pathology in schizophrenia, we studied the postmortem hippocampal sections of 16 patients suffering from schizophrenia and 16 controls applying the gray-level index (GLI) method. We determined the area-percentage covered by neuronal perikarya in relation to the total area of the pyramidal cell layer in the four subdivisions of the ammon's horn (cornu ammonis, CA1-4) bilaterally. Additionally, we determined the area size of the pyramidal cell layer (CA1-4) and dentate gyrus (DG) granule cell layer. Results showed no significant differences between diagnostic groups with respect to the dependent variables, supporting the view that there is no primary alteration of hippocampal gray matter in schizophrenia.

The macaque inferior parietal lobule: cytoarchitecture and distribution pattern of serotonin 5-HT1A binding sites

The inferior parietal lobule (IPL) of the macaque monkey integrates sensory information as a prerequisite for reaching and grasping movements. Electrophysiological data suggest that the convexity of the IPL is heterogeneous along its rostro-caudal axis. Cytoarchitecture reflects this functional diversity. However, various parcellations have been proposed so far, ranging from one homogeneous region to four areas. In order to obtain a more valid anatomical map of the IPL, we studied the distribution pattern of serotonin 5-HT1A binding sites (i.e., the domain of synaptic transmission and cortical information processing) and cytoarchitecture with an observer-independent technique (thus avoiding the subjectivity inherent in visually guided microstructural parcellations). We cut with a cryostat microtome four unfixed macaque hemispheres and processed sections for 5-HT1A binding sites with [3H]8-OH-DPAT receptor autoradiography or for cell bodies with a modified silver stain. We digitized the autoradiographs and the histological sections and extracted from the cortex of the IPL equidistant density profiles oriented vertically to the cortical layers. We then compared groups of neighboring profiles with multivariate statistics expecting to see a significant difference in profile shape at the interface between two cortical areas. These positions were compared between 5-HT1A autoradiographs (neurochemical borders) and adjacent histological sections (cytoarchitectonic borders). Neurochemical and cytoarchitectonic borders showed a good topographical correspondence and revealed three areas arranged in a rostro-caudal sequence along the convexity of the IPL. Dorsally, the areas extend approximately 1 mm into the depth of the lateral bank of the intraparietal sulcus. Their ventral border lies on the convexity of the IPL close to the shoulder of the lateral sulcus. The three areas are in close agreement with areas PF, PFG, and PG as defined by Pandya and Seltzer (J Comp Neurol 204:196-210, 1982) and Gregoriou et al. (Program No. 919.5, Abstract Viewer/Itinerary Planner, Washington, Society for Neuroscience, 2003). The neurochemical and cytoarchitectonic data show that a complex structural framework underlies the functional heterogeneity along the rostro-caudal axis of the IPL, e.g., the representation of different types of arm and hand actions in different sectors of the monkey's workspace.

Multimodal architectonic mapping of human superior temporal gyrus

Although it is generally accepted that human superior temporal gyrus is activated by a huge variety of auditory and linguistic tasks, little is known about the exact positions and extents of cortical areas that are located on the lateral convexity of the gyrus (e.g., Brodmann's area 22). Such information, however, is relevant for a rigorous testing of structural-functional relationships in both normal volunteers and patients suffering from disorders of auditory and language perception. The present combined cytoarchitectonic and receptorarchitectonic study identifies a distinct area (Te3) in the lateral bulge of the superior temporal gyrus by using an algorithm-based approach for the detection of cortical borders. Our mapping data show that, in contrast to Brodmann's area (BA) 22, only small portions of Te3 reach the dorsal and ventral banks of the gyrus. Therefore, we labelled the newly defined area as "Te3" and not as "BA 22". The cytoarchitectonically defined borders of Te3 coincide with abrupt changes in the receptorarchitecture of several classical neurotransmitters, suggesting that Te3 represents a functionally relevant area of the human superior temporal gyrus. Since position and extent of area Te3 varied considerably between subjects, probability maps were created that show for each voxel of the standard references space, the frequency with which Te3 was present in it. These maps, in combination with previously published maps of the primary auditory cortex, can directly be compared with functional imaging data, and may open new perspectives for the analysis of structural-functional correlations in the human auditory and language systems.

The Human Parietal Operculum. I. Cytoarchitectonic Mapping of Subdivisions

The human secondary somatosensory cortex (SII) is located on the parietal operculum, as shown by intraoperative stimulation and functional imaging studies. The position and extent of the anatomical correlates of this functionally defined region, however, are still unknown. We have therefore histologically mapped the putative anatomical correlates of the SII cortex in cell-body-stained histological sections of 10 human postmortem brains using quantitative cytoarchitectonic analysis. The gray level index (GLI), which is an indicator of the volume fraction of nerve cell bodies, was measured in the parietal operculum. GLI profiles as measures of the laminar pattern of the cortex were extracted perpendicular to cortical layers. Cytoarchitectonic borders were detected observer-independently by multivariate statistical analysis of the laminar profiles. Four cytoarchitectonic areas (termed OP 1-4) were identified. This cytoarchitectonic heterogeneity of the parietal operculum corresponds to results of functional imaging studies on the human SII cortex and data from non-human primates where multiple subregions within SII have been demonstrated by electrophysiological and connectivity studies.

Design-based stereology in neuroscience

Quantitative morphology of the CNS has recently undergone major developments. In particular, several new approaches, known as design-based stereologic methods, have become available and have been successfully applied to neuromorphological research. However, much confusion and uncertainty remains about the meaning, implications, and advantages of these design-based stereologic methods. The objective of this review is to provide some clarification. It does not comprise a full description of all stereologic methods available. Rather, it is written by users for users, provides the reader with a guided tour through the relevant literature. It has been the experience of the authors that most neuroscientists potentially interested in design-based stereology need to analyze volumes of brain regions, numbers of cells (neurons, glial cells) within these brain regions, mean volumes (nuclear, perikaryal) of these cells, length densities of linear biological structures such as vessels and nerve fibers within brain regions, and the cytoarchitecture of brain regions (i.e. the spatial distribution of cells within a region of interest). Therefore, a comprehensive introduction to design-based stereologic methods for estimating these parameters is provided. It is demonstrated that results obtained with design-based stereology are representative for the entire brain region of interest, and are independent of the size, shape, spatial orientation, and spatial distribution of the cells to be investigated. Also, it is shown that bias (i.e. systematic error) in results obtained with design-based stereology can be limited to a minimum, and that it is possible to assess the variability of these results. These characteristics establish the advantages of design-based stereologic methods in quantitative neuromorphology.

Evolution of the brainstem orofacial motor system in primates: a comparative study of trigeminal, facial, and hypoglossal nuclei

The trigeminal motor (Vmo), facial (VII), and hypoglossal (XII) nuclei of the brainstem comprise the final common output for neural control of most orofacial muscles. Hence, these cranial motor nuclei are involved in the production of adaptive behaviors such as feeding, facial expression, and vocalization. We measured the volume and Grey Level Index (GLI) of Vmo, VII, and XII in 47 species of primates and examined these nuclei for scaling patterns and phylogenetic specializations. Allometric regression, using medulla volume as an independent variable, did not reveal a significant difference between strepsirrhines and haplorhines in the scaling of Vmo volume. In addition, correlation analysis using independent contrasts did not find a relationship between Vmo size or GLI and the percent of leaves in the diet. The scaling trajectory of VII volume, in contrast, differed significantly between suborders. Great ape and human VII volumes, furthermore, were significantly larger than predicted by the haplorhine regression. Enlargement of VII in these taxa may reflect increased differentiation of the facial muscles of expression and greater utilization of the visual channel in social communication. The independent contrasts of VII volume and GLI, however, were not correlated with social group size. To examine whether the human hypoglossal motor system is specialized to control the tongue for speech, we tested human XII volume and GLI for departures from nonhuman haplorhine prediction lines. Although human XII volumes were observed above the regression line, they did not exceed prediction intervals. Of note, orang-utan XII volumes had greater residuals than humans. Human XII GLI values also did not differ from allometric prediction. In sum, these findings indicate that the cranial orofacial motor nuclei evince a mosaic of phylogenetic specializations for innervation of the facial muscles of expression in the context of a generally conservative scaling relationship with respect to medulla size.

Comparison of contrast, sensitivity and efficiency of signal amplified and nonamplified immunohistochemical reactions suitable for videomicroscopy-based quantification and neuroimaging

In recent years, many different technical modifications of immunohistochemical methods have been developed. The selection of a suitable technique for quantitative purposes such as mapping studies can be quite difficult. Various features of a certain method must be considered such as the sensitivity, costs, duration and practicability with respect to serial sectioned specimens. Background and foreground difference or contrast and the influence of artifacts are major problems of quantitative immunohistochemistry. It is not known which of the different modifications of immunohistochemical signal amplifications and non-amplifications gives optimal results in respect to image analytical-based quantification. However, for image analysis, it is important to analyze sections which offer a sufficient contrast between foreground and background. The sensitivity of a system is crucial when quantitative immunohistochemistry should be applied to scarce material with longer postmortem and storage times which occur often by processing human brains. In addition, the enzyme-substrate reactions have an obvious influence on this criterion; therefore, different substrates were also tested. The contrast may be as well effected by the quality and specificity of the primary antibody, the type of tissue and naturally by preparative (fixation, postmortem delay, storage) and individual factors (age, circadian effects, diseases, sex). Because all of these factors may yield to different results by combining them with different neuronal structures, we used three different antigen expressions for a specific analysis: fibrillary, granulary and perikaryal antigen distributions in brains from Wistar rats. Principally, the sensitivity of the modifications of immunohistochemical amplifications is revealed more strongly than without enhancement steps; however, the contrast between foreground and background structures does not necessary increase by applying a certain amplification technique. The lowest contrast (15%) was detected after applying the labelled streptavidin-biotin technique. All other methods offer comparable contrasts in between 30% and 40%. The catalyzed signal amplification reaction has been found to give optimal results (40% contrast) for image analysis. However, from the technical point of view and variability of protein expression, storage and postmortem delay, it was necessary to adapt the commercial CSA Kit from Dako (K1500). The modified technique, called C2 method, offers better results with respect to sensitivity, total costs, duration and contrast (60%) and variability of contrast.

Outstanding language competence and cytoarchitecture in Broca's speech region

Studies on brains of individuals with an exceptional mental capacity are of widespread interest. Here, we analyze the cytoarchitecture of areas 44 and 45 (anatomical correlates of Broca's speech region) of a person with a documented extraordinary competence in language performance (Emil Krebs, E.K.), and compared it with 11 control brains. Morphometry and multivariate statistical analysis revealed significant cytoarchitectonic differences between E.K. and the controls in left and right areas 44, in right 45, and in interhemispheric asymmetries. We conclude, that the exceptional language competence of E.K. may be related to distinct cytoarchitectonic features in Broca's region.

Analysis of neural mechanisms underlying verbal fluency in cytoarchitectonically defined stereotaxic space—The roles of Brodmann areas 44 and 45

We investigated neural activations underlying a verbal fluency task and cytoarchitectonic probabilistic maps of Broca's speech region (Brodmann's areas 44 and 45). To do so, we reanalyzed data from a previous functional magnetic resonance imaging (fMRI) [Brain 125 (2002) 1024] and from a cytoarchitectonic study [J. Comp. Neurol. 412 (1999) 319] and developed a method to combine both data sets. In the fMRI experiment, verbal fluency was investigated in 11 healthy volunteers, who covertly produced words from predefined categories. A factorial design was used with factors verbal class (semantic vs. overlearned fluency) and switching between categories (no vs. yes). fMRI data analysis employed SPM99 (Statistical Parametric Mapping). Cytoarchitectonic maps of areas 44 and 45 were derived from histologic sections of 10 postmortem brains. Both the in vivo fMRI and postmortem MR data were warped to a common reference brain using a new elastic warping tool. Cytoarchitectonic probability maps with stereotaxic information about intersubject variability were calculated for both areas and superimposed on the functional data, which showed the involvement of left hemisphere areas with verbal fluency relative to the baseline. Semantic relative to overlearned fluency showed greater involvement of left area 45 than of 44. Thus, although both areas participate in verbal fluency, they do so differentially. Left area 45 is more involved in semantic aspects of language processing, while area 44 is probably involved in high-level aspects of programming speech production per se. The combination of functional data analysis with a new elastic warping tool and cytoarchitectonic maps opens new perspectives for analyzing the cortical networks involved in language.

Broca's region: cytoarchitectonic asymmetry and developmental changes

Functional imaging and clinical studies in children and adults have provided evidence of developmental changes in the hemispheric specialization for language. Whereas cytoarchitectonic asymmetry has been demonstrated in Broca's region of adults, the anatomical correlates of developmental changes in language dominance are largely unknown. In the present postmortem study of 34 human brains (ages ranging from 3.5 months to 85 years), the cytoarchitecture of areas 44 and 45 as the putative anatomical correlates of Broca's region, their developmental changes, and interhemispheric asymmetry were analyzed. Asymmetry as estimated by Euclidean distances between feature vectors of cytoarchitectonic profiles of left and right areas 44 and 45 was already found in 1-year-old infants. Asymmetry tended to increase with age, which was significant in area 45, but not in area 44. An adult-like, left-larger-than-right asymmetry in the volume fraction of cell bodies [gray level index (GLI)] was reached at approximately 5 years in area 45 and 11 years in area 44. These time points indicate a delayed development of the cytoarchitectonic asymmetry in Broca's region in comparison with that of the primary motor cortex. It may be hypothesized that the delayed maturation is the microstructural basis of the development of language abilities and the influence of language practice on cytoarchitecture during childhood. Interhemispheric asymmetry in the cytoarchitecture of areas 44 and 45 continues to change throughout life. We conclude that the cytoarchitectonic asymmetry of areas 44 and 45 is a result of microstructural plasticity that endures throughout almost the whole lifespan.

Analyzing the neocortical fine-structure

Cytoarchitectonic fields of the human neocortex are defined by characteristic variations in the composition of a general six-layer structure. It is commonly accepted that these fields correspond to functionally homogeneous entities. Diligent techniques were developed to characterize cytoarchitectonic fields by staining sections of post-mortem brains and subsequent statistical evaluation. Fields were found to show a considerable interindividual variability in extent and relation to macroscopic anatomical landmarks. With upcoming new high-resolution magnetic resonance imaging (MRI) protocols, it appears worthwhile to examine the feasibility of characterizing the neocortical fine-structure from anatomical MRI scans, thus, defining neocortical fields by in vivo techniques. A fixated brain hemisphere was scanned at a resolution of approximately 0.3 mm. After correcting for intensity inhomogeneities in the dataset, the cortex boundaries (the white/grey matter and grey matter/background interfaces) were determined as a triangular mesh. Radial intensity profiles following the shortest path through the cortex were computed and characterized by a sparse set of features. A statistical similarity measure between features of different regions was defined, and served to define the extent of Brodmann's Areas 4, 17, 44 and 45 in this dataset.

Automated image analysis of disturbed cytoarchitecture in Brodmann area 10 in schizophrenia

To detect cytoarchitectonic abnormalities in the Brodmann area 10 (BA10) of schizophrenic patients, we applied a newly modified variant of the gray-level index (GLI) method as fully automated image analysis method providing cytoarchitectonic profiles of the whole cortex as a scanning tool. Microscopic images of silver-stained sections of 20 schizophrenic brains compared to 20 control brains were automatically scanned and binarized at an adaptive threshold. In 30 measuring fields through the whole cortical depth, the dependent measure of gray-level index (GLI) as the area-percentage covered by perikarya in a measuring field was obtained providing a cytoarchitectonic profile. GLI is an estimate of the volume density of perikarya. A statistical analysis of mean GLI values was performed for six compartments, separately, approximately corresponding to cortical layers. Results revealed significant GLI reductions in schizophrenic brains in all six compartments suggesting either a decreased perikarya fraction or an increased neuropil fraction. The described automated image analysis method providing cytoarchitectonic profiles can be applied as a fast and observer-independent scanning tool to detect cytoarchitectonic abnormalities in multiple brain regions.

Detection of cortical transition regions utilizing statistical analyses of excess masses

A new statistical approach for observer-assisted detection of transition regions of adjacent cytoarchitectonic areas within the human cerebral cortex was developed. This method analyzes the structural information of cytoarchitectural profiles (e.g., the modality of a gray level intensity distribution) based on observed excess mass differences verified by a suitable statistical test. Profiles were generated by scanning the cerebral cortex over respective regions of interest that were oriented to trajectories running parallel to the orientation of cell columns. For each single profile, determination of excess masses provided evidence for a certain number of peaks in the cell density, thereby avoiding fluctuation due solely to sampling anomalies. Comparing such excess mass measurements by means of multiple local rank tests over a wide range of profiles allowed for the detection of cytoarchitectural inhomogeneities at respective given confidence levels. Special parameters (e.g., level of significance, width of targeted region, number of peaks) then could be adapted to specific pattern recognition problems in lamination analyses. Such analyses of excess masses provided a general tool for observer-assisted evaluation of profile arrays. This observer-assisted statistical method was applied to five different cortical examples. It detected the same transition regions that had been determined earlier through direct examination of samples, despite cortical convexities, concavities, and some minor staining inhomogeneities.

Neural activity in human primary motor cortex areas 4a and 4p is modulated differentially by attention to action

The mechanisms underlying attention to action are poorly understood. Although distracted by something else, we often maintain the accuracy of a movement, which suggests that differential neural mechanisms for the control of attended and nonattended action exist. Using functional magnetic resonance imaging (fMRI) in normal volunteers and probabilistic cytoarchitectonic maps, we observed that neural activity in subarea 4p (posterior) within the primary motor cortex was modulated by attention to action, while neural activity in subarea 4a (anterior) was not. The data provide the direct evidence for differential neural mechanisms during attended and unattended action in human primary motor cortex.

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.

Human somatosensory area 2: observer-independent cytoarchitectonic mapping, interindividual variability, and population map

We analyzed the topographical variability of human somatosensory area 2 in 10 postmortem brains. The brains were serially sectioned at 20 microm, and sections were stained for cell bodies. Area 2 was delineated with an observer-independent technique based on significant differences in the laminar densities of cell bodies. The sections were corrected with an MR scan of the same brain obtained before histological processing. Each brain's histological volume and representation of area 2 was subsequently reconstructed in 3-D. We found that the borders of area 2 are topographically variable. The rostral border lies between the convexity of the postcentral gyrus and some millimeters deep in the rostral wall of the postcentral sulcus. The caudal border lies between the fundus of the postcentral sulcus and some millimeters above it in the rostral wall. In contrast to Brodmann's map, area 2 does not extend onto the mesial cortical surface or into the intraparietal sulcus. When the postcentral sulcus is interrupted by a gyral bridge, area 2 crosses this bridge and is not separated into two segments. After cytoarchitectonic analysis, the histological volumes were warped to the reference brain of a computerized atlas and superimposed. A population map was generated in 3-D space, which describes how many brains have a representation of area 2 in a particular voxel. This microstructurally defined population map can be used to demonstrate activations of area 2 in functional imaging studies and therefore help to further understand the role of area 2 in somatosensory processing.

Human primary auditory cortex: cytoarchitectonic subdivisions and mapping into a spatial reference system

The transverse temporal gyrus of Heschl contains the human auditory cortex. Several schematic maps of the cytoarchitectonic correlate of this functional entity are available, but they present partly conflicting data (number and position of borders of the primary auditory areas) and they do not enable reliable comparisons with functional imaging data in a common spatial reference system. In order to provide a 3-D data set of the precise position and extent of the human primary auditory cortex, its putative subdivisions, and its topographical intersubject variability, we performed a quantitative cytoarchitectonic analysis of 10 brains using a recently established technique for observer-independent definition of areal borders. Three areas, Te1.1, Te1.0, and Te1.2, with a well-developed layer IV, which represent the primary auditory cortex (Brodmann area 41), can be identified along the mediolateral axis of the Heschl gyrus. The cell density was significantly higher in Te1.1 compared to Te1.2 in the left but not in the right hemisphere. The cytoarchitectonically defined areal borders of the primary auditory cortex do not consistently match macroanatomic landmarks like gyral and sulcal borders. The three primary auditory areas of each postmortem brain were mapped to a spatial reference system which is based on a brain registered by in vivo magnetic resonance imaging. The integration of a sample of postmortem brains in a spatial reference system allows one to estimate the spatial variability of each cytoarchitectonically defined region with respect to this reference system. In future, the transfer of in vivo structural and functional data into the same spatial reference system will enable accurate comparisons of cytoarchitectonic maps of the primary auditory cortex with activation centers as established with functional imaging procedures.

Prefrontal cortex in humans and apes: a comparative study of area 10

Area 10 is one of the cortical areas of the frontal lobe involved in higher cognitive functions such as the undertaking of initiatives and the planning of future actions. It is known to form the frontal pole of the macaque and human brain, but its presence and organization in the great and lesser apes remain unclear. It is here documented that area 10 also forms the frontal pole of chimpanzee, bonobo, orangutan, and gibbon brains. Imaging techniques and stereological tools are used to characterize this area across species and provide preliminary estimates of its absolute and relative size. Area 10 has similar cytoarchitectonic features in the hominoid brain, but aspects of its organization vary slightly across species, including the relative width of its cortical layers and the space available for connections. The cortex forming the frontal pole of the gorilla appears highly specialized, while area 10 in the gibbon occupies only the orbital sector of the frontal pole. Area 10 in the human brain is larger relative to the rest of the brain than it is in the apes, and its supragranular layers have more space available for connections with other higher-order association areas. This suggests that the neural substrates supporting cognitive functions associated with this part of the cortex enlarged and became specialized during hominid evolution.

Broca's region subserves imagery of motion: a combined cytoarchitectonic and fMRI study

Broca's region in the dominant cerebral hemisphere is known to mediate the production of language but also contributes to comprehension. Here, we report the differential participation of Broca's region in imagery of motion in humans. Healthy volunteers were studied with functional magnetic resonance imaging (fMRI) while they imagined movement trajectories following different instructions. Imagery of right-hand finger movements induced a cortical activation pattern including dorsal and ventral portions of the premotor cortex, frontal medial wall areas, and cortical areas lining the intraparietal sulcus in both cerebral hemispheres. Imagery of movement observation and of a moving target specifically activated the opercular portion of the inferior frontal cortex. A left-hemispheric dominance was found for egocentric movements and a right-hemispheric dominance for movement characteristics in space. To precisely localize these inferior frontal activations, the fMRI data were coregistered with cytoarchitectonic maps of Broca's areas 44 and 45 in a common reference space. It was found that the activation areas in the opercular portion of the inferior frontal cortex were localized to area 44 of Broca's region. These activations of area 44 can be interpreted to possibly demonstrate the location of the human analogue to the so-called mirror neurones found in inferior frontal cortex of nonhuman primates. We suggest that area 44 mediates higher-order forelimb movement control resembling the neuronal mechanisms subserving speech.

Automated image analysis of disturbed cytoarchitecture in Brodmann area 10 in schizophrenia: a post-mortem study

1. Among different etiological concepts in schizophrenia research is the disconnect on hypothesis involving distributed brain regions. Adequate empirical research requires correlational studies of multiple brain regions. In this pilot study, the authors therefore tested the applicability of an automated image analysis device as a scanning tool to detect cytoarchitectural abnormalities in Brodmann area (BA) 10. 2. The authors applied the gray level index (GLI) method as automated image analysis on 10 schizophrenic brains compared to 10 controls. The GLI as perikarya-neuropil-ratio is obtained as the ratio between the area covered by cellular cross sections and the area of the total measuring field in 101 continous measuring fields from pial surface to the cortical depth. Resulting data provide a specific cytoarchitectonic profile curve. An analysis was performed separately for mean GLI and GLI values in six compartments covering approximately the different cortical laminae. 3. A statistically significant reduction of the mean GLI was demonstrated in the schizophrenic group covering laminae III to VI, as detected by multivariate analysis and corroborated by univariate analyses and t-tests. 4. This result clearly underlines a cytoarchitectonic disturbance with a perikarya neuropil-ratio reduction in BA 10, that is associated with schizophrenia. This is suggestive either of an increased neuropil fraction or a decreased neuronal perikarya fraction. The latter could either be due to a volume or a total number reduction of neuronal perikarya. These data are compatible with previously published data on cell loss in schizophrenics in BA 10.

A stereological approach to human cortical architecture: identification and delineation of cortical areas

Stereology offers a variety of procedures to analyze quantitatively the regional and laminar organization in cytoarchitectonically defined areas of the human cerebral cortex. Conventional anatomical atlases are of little help in localizing specific cortical areas, since most of them are based on a single brain and use highly observer-dependent criteria for the delineation of cortical areas. In consequence, numerous cortical maps exist which greatly differ with respect to number, position, size and extent of cortical areas. We describe a novel algorithm-based procedure for the delineation of cortical areas, which exploits the automated estimation of volume densities of cortical cell bodies. Spatial sampling of the laminar pattern is performed with density profiles, followed by multivariate analysis of the profiles' shape, which locates the cytoarchitectonic borders between neighboring cortical areas at sites where the laminar pattern changes significantly. The borders are then mapped to a human brain atlas system comprising tools for three dimensional reconstruction, visualization and morphometric analysis. A sample of brains with labeled cortical areas is warped into the reference brain of the atlas system in order to generate a population map of the cortical areas, which describes the intersubject variability in spatial conformation of cortical areas. These population maps provide a novel tool for the interpretation of images obtained with functional imaging techniques.

Coordinate-independent mapping of structural and functional data by objective relational transformation (ORT)

Neuroscience has produced an enormous amount of structural and functional data. Powerful database systems are required to make these data accessible for computational approaches such as higher-order analyses and simulations. Available databases for key data such as anatomical and functional connectivity between cortical areas, however, are still hampered by methodological problems. These problems arise predominantly from the parcellation problem, the use of incongruent parcellation schemes by different authors. We here present a coordinate-independent mathematical method to overcome this problem: objective relational transformation (ORT). Based on new classifications for brain data and on methods from theoretical computer science, ORT represents a formally defined, transparent transformation method for reproducible, coordinate-independent mapping of brain data to freely chosen parcellation schemes. We describe the methodology of ORT and discuss its strengths and limitations. Using two practical examples, we show that ORT in conjunction with connectivity databases like CoCoMac (http://www.cocomac.org) is an important tool for analyses of cortical organization and structure-function relationships.

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.

Essential functions of the human self model are implemented in the prefrontal cortex

The human self model comprises essential features such as the experiences of ownership, of body-centered spatial perspectivity, and of a long-term unity of beliefs and attitudes. In the pathophysiology of schizophrenia, it is suggested that clinical subsyndromes like cognitive disorganization and derealization syndromes reflect disorders of this self model. These features are neurobiologically instantiated as an episodically active complex neural activation pattern and can be mapped to the brain, given adequate operationalizations of self model features. In its unique capability of integrating external and internal data, the prefrontal cortex (PFC) appears to be an essential component of the neuronal implementation of the self model. With close connections to other unimodal association cortices and to the limbic system, the PFC provides an internally represented world model and internal milieu data of the organism, both serving world orientation. In the pathophysiology of schizophrenia, it is the dysfunction of the PFC that is suggested to be the neural correlate for the different clinical schizophrenic subsyndromes. The pathophysiological study of psychiatric disorders may contribute to the theoretical debate on the neuronal basis of the self model.

Areas 3a, 3b, and 1 of human primary somatosensory cortex

This study defines cytoarchitectonic areas 3a, 3b, and 1 of the human primary somatosensory cortex by objective delineation of cytoarchitectonic borders and ensuing cytoarchitectonic classification. This avoids subjective evaluation of microstructural differences which has so far been the only way to structurally define cortical areas. Ten brains were fixed in formalin or Bodian's fixative, embedded in paraffin, sectioned as a whole in the coronal plane at 20 microm, and cell stained. Cell bodies were segmented from the background by adaptive thresholding. Equidistant density profiles (125 microm wide, spacing 300 or 150 microm) were extracted perpendicularly to the pial surface across cortical layers II-VI and processed with multivariate statistical procedures. Positions of significant differences in shape between adjacent groups of profiles were correlated with the cytoarchitectonic pattern. Statistically significant borders can be reproduced at corresponding positions across a series of nearby sections. They match visible changes in cytoarchitecture in the cell-stained sections. Area 3a lies in the fundus of the central sulcus, and area 3b in the rostral bank of the postcentral gyrus. Area 1 lies on its crown and reaches down into the postcentral sulcus. Interareal borders, however, do not match macrostructural landmarks of the postcentral gyrus, and they considerably vary in their positions relative to these landmarks across different brains. Hence, only genuine microstructural analysis can define the borders between these cortical areas. Additional significant borders which do not correlate with visible changes in cytoarchitecture can be found within areas 3b and 1. They may represent somatotopy and/or cortical representations of different somatosensory receptors.

Optimal staining methods for delineation of cortical areas and neuron counts in human brains

For cytoarchitectonic delineation of cortical areas in human brain, the Gallyas staining for somata with its sharp contrast between cell bodies and neuropil is preferable to the classical Nissl staining, the more so when an image analysis system is used. This Gallyas staining, however, does not appear to be appropriate for counting neuron numbers in pertinent brain areas, due to the lack of distinct cytological features between small neurons and glial cells. For cell counting Nissl is preferable. In an optimal design for cell counting at least both the Gallyas and the Nissl staining must be applied, the former staining for cytoarchitectural delineaton of cortical areas and the latter for counting the number of neurons in the pertinent cortical areas.

Observer-independent method for microstructural parcellation of cerebral cortex: A quantitative approach to cytoarchitectonics

We describe a new, observer-independent procedure for identifying boundaries between cortical areas. The method is useful for images obtained from sections which provide microstructural information on the cortical laminar pattern, e.g., Nissl-, myelin-, or immunohistochemically stained sections or receptor autoradiographs. The laminar pattern is represented by profile curves extending from the cortical surface to the white matter boundary. These profiles are constructed from digitized images. Digitization is based on the grey level index (Nissl) or densitometry (myelin, immunohistochemistry, receptor autoradiography). The shapes of neighboring profiles are compared by calculating their distances according to feature vectors extracted from the profiles. Profiles derived from a homogeneous area can be expected to be similar in shape and hence show low distance values between each other. Maximum distances can be found between profiles which lie on opposite sides of a structural boundary. The Mahalanobis distance was found to be more sensitive and to yield greater spatial resolution than other distance measures such as the Euclidean distance. Cell-stained sections of the human neocortex were analyzed. The method not only verified boundaries which had been defined by visual inspection, it also revealed new ones which had not been detected visually. The procedure offers an important supplement to the traditional methods based on visual inspection which, for the first time, is based on quantitative data and therefore offers a new level of reproducibility and observer independence. Anatomical atlases based on this procedure thus provide a new tool for the interpretation of structural data obtained from functional imaging techniques.

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.

Structural divisions and functional fields in the human cerebral cortex

The question of what is a cortical area needs a thorough definition of borders both in the microstructural and the functional domains. Microstructural parcellation of the human cerebral cortex should be made on multiple criteria based on quantitative measurements of microstructural variables, such as neuron densities, neurotransmitter receptor densities, enzyme densities, etc. Because of the inter-individual variations of extent and topography of microstructurally defined areas, the final microstructurally defined areas appear as population maps. In the functional domain, columns, patches and blobs signifying synaptically active parts of the cortex appear as cortical functional fields. These fields are the largest functional entities of the cerebral cortex according to the cortical field hypothesis. In its strong version, the cortical field hypothesis postulates that all neurons and synapses within the fields perform a co-operative computation. A number of such fields together provide the functional contribution of the cerebral cortex. The functional parcellation of the human cerebral cortex must be based on field population maps, which after intersection analysis appear as functional domains. The major structural-functional hypothesis to be examined is whether these functional domains are equi-territorial to the microstructurally defined meta-maps. The cortical hypothesis predicts that, if two brain tasks make use of one or several identical or largely overlapping fields, they cannot be performed simultaneously without errors or increases in latency. Evidence for such interference is presented. This evidence represents a restriction in the parallel processing of the human brain. In the posterior part of the brain not only visual cortical areas may qualify for parallel processing, but also the somatosensory cortices appear to have separate functional streams for the detection of microgeometry and macrogeometry.

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.

Two different areas within the primary motor cortex of man

The primary motor area (M1) of mammals has long been considered to be structurally and functionally homogeneous. This area corresponds to Brodmann's cytoarchitectural area 4. A few reports showing that arm and hand are doubly represented in M1 of macaque monkeys and perhaps man, and that each subarea has separate connections from somatosensory areas, have, with a few exceptions, gone largely unnoticed. Here we show that area 4 in man can be subdivided into areas '4 anterior' (4a) and '4 posterior' (4p) on the basis of both quantitative cytoarchitecture and quantitative distributions of transmitter-binding sites. We also show by positron emission tomography that two representations of the fingers exist, one in area 4a and one in area 4p. Roughness discrimination activated area 4p significantly more than a control condition of self-generated movements. We therefore suggest that the primary motor area is subdivided on the basis of anatomy, neurochemistry and function.

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.

Inhibition of angiogenesis in vitro and in ovo with an inhibitor of cellular protein kinases, MDL 27032

Protein kinase C (PKC) was implicated as an important positive regulator of angio-genesis by studies showing that tumor promoting phorbol esters, which activate PKC, stimulate angiogenesis both in vitro and in vivo. Therefore, inhibitors of PKC might be expected to block angiogenesis. MDL 27032 [4-propyl-5-(4-pyridinyl)-2(3H)-oxazolone], an inhibitor of cellular protein kinases, prevented capillary-like tube formation by human umbilical vein endothelial cells (HUVEC) on basement membrane preparations, an in vitro model for angiogenic activity. MDL 27032 had an IC50 = 50 microM, whereas MDL 27044, the 4-methyl analog of MDL 27032, was less effective (IC50 greater than 100 microM). This selectivity was reflected in the relative abilities of the two compounds to inhibit PKC and protein kinase A (PKA) activity prepared from HUVEC, and also to inhibit the basic fibroblast growth factor stimulated proliferation of HUVEC. MDL 27032 (0.3 microgram/egg) also significantly inhibited neovascularization in yolk sac membranes of developing chick embryos, whereas MDL 27044 added at concentrations up to 3 micrograms/egg was not inhibitory when compared with vehicle treated controls. Adhesion of HUVEC to individual extracellular matrix proteins, including laminin, fibronectin, and fibrinogen, but not to the mixture of matrix components or collagen type I and IV, was inhibited after treatment with MDL 27032. These studies suggest that MDL 27032, may have potential as an anti-angiogenic agent because it disrupts both formation of tube-like structures by HUVEC on Matrigel and normal neovascularization in ovo. This inhibition may in part be due to altered cellular interactions with the extracellular matrix.

Quantitative morphology of the nervous system: expanding horizons

In this review, we show how some of the recent developments in quantitative morphology (QM) are creating exciting new opportunities for studying the structure of the nervous system. We begin with a brief overview of QM, focusing on the problems neurobiologists are likely to encounter when collecting and interpreting data from tissue sections. Many of these problems, which range from selecting a sampling method to learning the latest methods, are being solved by creating a new generation of research tools. We describe several of these new tools and show how they can be used to assemble new quantitative methods for in situ hybridization, immunocytochemistry, and camera lucida drawings. The review includes examples of how QM is being used to study the brain and concludes with a brief discussion of diagnostic pathology and its need for new quantitative approaches.

Stereology: a method for analyzing images

This review deals with notions of shape, sizes, numbers, densities and orientation in space, all basic concepts in stereology. With the initiation by Delesse in 1847, but mainly since the beginning of the XXth century, many stereological methods have been published allowing us to relate two-dimensional measurements easily obtainable on flat histological images with three-dimensional characteristics of the structure analysed. Looking at these methods, the neurobiologist, generally impermeable to concepts of sampling, statistical bias, efficiency, cost of effort and distribution-free, is discountenanced and continues old laboratory usages and customs. Furthermore, for the last ten years, the advent of a plethora of new powerful tools, considered as assumption-free and more efficient than the previous ones, increase the risk proportionately the disarray of the potential user. The purpose of this review is to present synthetically all traditional and actual aspects of stereology in order to guide the reader in the labyrinth of this speciality. The necessarily short exposition is compensated by many references to which the beginner or the initiated can refer.