Thorsten Schormann

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 Brodmanns 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 Brodmanns 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 subserves imagery of motion: a combined cytoarchitectonic and fMRI study.

Brocas 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 Brocas 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 Brocas 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 Brocas 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. Hum. Brain Mapping 11:273–285, 2000.

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 brains 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 Brodmanns 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.

Areas 3a, 3b, and 1 of human primary somatosensory cortex: 2. Spatial normalization to standard anatomical space

Interindividual topographical variability of cytoarchitectonically defined somatosensory areas 3a, 3b, and 1 was analyzed in the standard anatomical format of a computerized brain atlas. T1-weighted magnetic resonance images were obtained from 10 postmortem brains. The brains were serially sectioned at 20 mcm, sections were stained for cell bodies, and areas 3a, 3b, and 1 were defined with an observer-independent cytoarchitectonic technique. After correction of the sections for deformations due to histological processing, the 3-D reconstructed histological volumes of the individual brains and the volume representations of the cytoarchitectonic areas were adapted to the reference brain of a computerized atlas. Corresponding areas were superimposed in the 3-D space of the reference brain. These population maps describe, for each voxel, how many brains have a representation of one particular cytoarchitectonic area. Each areas extent is very variable across different brains, but representations of areas 3a, 3b, and 1 in >/=50% of the brains were found in the fundus of the central sulcus, its caudal bank, and on the crown of the postcentral gyrus, respectively. Volumes of interest (VOIs) were defined for each area in which >/=50% of the brains have a representation of that area. Despite close spatial relationship of areas 3a, 3b, and 1 in the postcentral gyrus, the three VOIs overlap by <1% of their volumes. Functional imaging data can now be brought into the same standard anatomical format, and changes in regional cerebral blood flow can be calculated in VOIs of areas 3a, 3b, and 1, which are derived from genuine cytoarchitectonic data.

Quantitative analysis of sulci in the human cerebral cortex: Development, regional heterogeneity, gender difference, asymmetry, intersubject variability and cortical architecture

The degree of cortical folding (GI) and the relation between sulci and borders of cyto‐ and receptorarchitectonically defined areas were analyzed in postmortem human brains. The GI reaches adult levels (with highest values in the association cortices) around birth and does not decrease during aging. It shows a sex‐dependent left‐over‐right asymmetry. Sulci and borders of architectonical areas coincide only in a few examples; thus, sulci are not generally valid landmarks of the microstructural organization of the cortex.

Three-dimensional linear and nonlinear transformations: an integration of light microscopical and MRI data.

The registration of image volumes derived from different imaging modalities such as MRI, PET, SPECT, and CT has been described in numerous studies in which functional and morphological data are combined on the basis of macrostructural information. However, the exact topography of architectural details is defined by microstructural information derived from histological sections. Therefore, a technique is developed for integrating micro‐ and macrostructural information based on 1) a three‐dimensional reconstruction of the histological volume which accounts for linear and nonlinear histological deformations, and 2) a two‐step procedure which transforms these volumes to a reference coordinate system. The two‐step procedure uses an extended principal axes transformation (PAT) generalized to affine transformations and a fast, automated full‐multigrid method (FMG) for determining high‐dimensional three‐dimensional nonlinear deformations in order to account for differences in the morphology of individuals. With this technique, it is possible to define upwards of 1,000 times the resolution of ∼1 mm in MRI, making possible the identification of geometric and texture features of microscopically defined brain structures. Hum. Brain Mapping 6:339–347, 1998.

Correlation between human personality and neural activity in cerebral cortex.

Personality traits are a variance of behavioral patterns among individuals and may reflect a variance of brain activity, but their neurobiological explanation is still a matter of debate. Cloninger proposed three dimensions of personality traits, each of which has strong correlation with activity in a specific central monoaminergic system. Although this theory has been supported by physiological and genetic studies, it is still unclear how these personality parameters are correlated with the activity of the cortical networks which control human behavior. Here we measured the regional cerebral blood flow (rCBF) at rest in 30 normal volunteers who completed the personality inventory of Cloninger. Voxel-by-voxel analysis was employed to identify cortical regions where the rCBF showed significant correlation with any of the three personality parameters. Statistically significant correlation was observed in several paralimbic and neocortical regions and was consistent with the assumed monoaminergic influence on neural activity and the distribution of its projections, in each personality dimension. The results suggest that activity in a variety of cortical regions is associated with human personality traits and lend support to Cloningers theory concerning central monoaminergic influence on human personality traits.

A New Approach to Fast Elastic Alignment with Applications to Human Brain

A technique is presented for elastic alignment applicable to human brains. The transformation which minimizes the distance measure D(u) between template and reference is determined, thereby simultaneously satisfying smoothness constraints derived from an elastic potential known from the theory of kontinuum mechanics. The resulting partial differential equations, with up to 3·220 unknowns are directly solved for each voxel, that is, without interpolation, by an adapted full multigrid-method (FMG) providing a perfect alignment. For further increases of resolution, the full advantages of the FMG are maintained, that is, parallelization and linear effort with O(N), N being the number of grid-points.

Comparison of spatial normalization procedures and their impact on functional maps

The alignment accuracy and impact on functional maps of four spatial normalization procedures have been compared using a set of high resolution brain MRIs and functional PET volumes acquired in 20 subjects. Simple affine (AFF), fifth order polynomial warp (WRP), discrete cosine basis functions (SPM), and a movement model based on full multi grid (FMG) approaches were applied on the same dataset for warping individual volumes onto the Human Brain Atlas (HBA) template. Intersubject averaged structural volumes and tissue probability maps were compared across normalization methods and to the standard brain. Thanks to the large number of degrees of freedom of the technique, FMG was found to provide enhanced alignment accuracy as compared to the other three methods, both for the grey and white matter tissues; WRP and SPM exhibited very similar performances whereas AFF had the lowest registration accuracy. SPM, however, was found to perform better than the other methods for the intra‐cerebral cerebrospinal fluid (mainly in the ventricular compartments). Limited differences in terms of activation morphology and detection sensitivity were found between low resolution functional maps (FWHM ∼10 mm) spatially normalized with the four methods, which overlapped in 42.8% of the total activation volume. These findings suggest that the functional variability is much larger than the anatomical one and that precise alignment of anatomical features has low influence on the resulting intersubject functional maps. When increasing the spatial resolution to approximately 6 mm, however, differences in localization of activated areas appear as a consequence of the different spatial normalization procedure used, restricting the overlap of the normalized activated volumes to only 6.2%. Hum. Brain Mapping 16:228–250, 2002.

Cytoarchitectural maps of the human brain in standard anatomical space

The remarkable intersubject variability of the human cerebral cortex poses major problems for the systematic study of functional‐structural relationships. Lack of homology and macroscopical landmarks between brains implies that one cannot in three or two dimensions find which part of one gyrus or sulcus matches which part of another subjects cerebral cortex. Furthermore, the frequent lack of correspondence between cytoarchitectural borders and the bottom of sulci invalidates correlations between gross morphology and microstructure. Therefore, we proposed that microstructural criteria should be used to define an anatomical space for comparison of individual brains and for establishing a probability map for each cytoarchitecturally defined area by quantitative means [Roland and Zilles, 1994; Trends Neurosci 17:458–467]. Here we examined the mapping of cytoarchitectural areas 4a, 4p, 3a, 3b, V1, and V2 into two commonly used anatomical standard reference spaces. Linear global transformations into Talairach space produced minimal overlap of corresponding cytoarchitectural areas. Global affine and nonaffine transformations into the anatomical space of the Human Brain Atlas (HBA) gave significantly larger volumes of overlap of corresponding cytoarchitectural areas. It is expected that local transformations can further improve the registration of corresponding cytoarchitectural areas and thereby define a common standard anatomical space in which to study variations in gross anatomical structure and function. Hum. Brain Mapping 5:222–227, 1997.