T. Schormann

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.

Probabilistic Mapping and Volume Measurement of Human Primary Auditory Cortex

Despite their potential utility in clinical and research settings, the range of intra- and interindividual variations in size and location of cytoarchitectonically defined human primary auditory cortex (PAC) is largely unknown. This study demonstrates that gyral patterns and the size and location of PAC vary independently to a considerable degree. Thus, the cytoarchitectonic borders of PAC cannot be reliably inferred from macroscopic-MR visible-anatomy. Given the remarkable topographical variability of architectonic areal borders, standard brain mapping which is made solely on the basis of macroanatomic landmarks may lead to structural-functional mismatch. Consequently, interpretations of individual auditory activity patterns might often be inaccurate. In view of the anatomic discrepancies, we generated probability maps of PAC in which the degree of intersubject overlap in each stereotaxic position was quantified. These maps show that the location of PAC in Talairach space differs considerably between hemispheres and individuals. In contrast to earlier cytoarchitectonic work which is based in most cases on studies of single brains, our systematic approach provides extensive microanatomic data as a reference system for studies of human auditory function.

Mapping of histologically identified long fiber tracts in human cerebral hemispheres to the MRI volume of a reference brain: position and spatial variability of the optic radiation.

The interpretation of the anatomical basis of functional deficits after subcortical infarcts could be considerably improved, if the precise topography and interindividual variability in size and course of long fiber tracts in adult human cerebral hemispheres were available in a spatial reference system. We therefore developed a method enabling the mapping of long fiber tracts to the volume of a standard reference brain. The examined fiber tracts were identified in myelin-stained histological serial sections of 10 human brains. The reference brain is a 3-D reconstruction of in vivo obtained magnetic resonance images (MRIs). The warping of histological volumes with the labeled fiber tracts to the reference brain by means of linear and nonlinear transformation procedures results in population maps that demonstrate the interindividual variability in position, size, and course of fiber tracts. In this paper, we present population maps of the optic radiation and the lateral geniculate body as a first example of this mapping strategy. Both structures present a considerable interindividual variability. Furthermore, voxel-based morphometry shows significant side differences with larger volumes of both structures in the left hemisphere than in the right hemisphere. A more than twofold variability of size in the interhemispheric extension of the optic radiation and the lateral geniculate body is found even after normalization of absolute brain size. Our observations demonstrate that the present approach based on population maps of fiber tracts and nuclei can improve the anatomical localization and interpretation of brain lesions visible in MRIs at the level of microstructurally identified architectonical units.

Activation Reduction in Anterior Temporal Cortices during Repeated Recognition of Faces of Personal Acquaintances

Repeated recognition of the face of a familiar individual is known to show semantic repetition priming effect. In this study, normal subjects were repeatedly presented faces of their colleagues, and the effect of repetition on the regional cerebral blood flow change was measured using positron emission tomography. They repeated a set of three tasks: the familiar-face detection (F) task, the facial direction discrimination (D) task, and the perceptual control (C) task. During five repetitions of the F task, familiar faces were presented six times from different views in a pseudorandom order. Activation reduction through the repetition of the F tasks was observed in the bilateral anterior (anterolateral to the polar region) temporal cortices which are suggested to be involved in the access to the long-term memory concerning people. The bilateral amygdala, the hypothalamus, and the medial frontal cortices, were constantly activated during the F tasks, and considered to be associated with the behavioral significance of the presented familiar faces. Constant activation was also observed in the bilateral occipitotemporal regions and fusiform gyri and the right medial temporal regions during perception of the faces, and in the left medial temporal regions during the facial familiarity detection task, which are consistent with the results of previous functional brain imaging studies. The results have provided further information about the functional segregation of the anterior temporal regions in face recognition and long-term memory.

Activation in the ipsilateral posterior parietal cortex during tool use: a PET study.

The basis of perceptual assimilation of tool and hand has been considered to be in modification of body schemata, for which integration of multimodal sensory information about our body parts is required. Using positron emission tomography and H(2)(15)O, we aimed to identify brain regions that change their neural activity in association with changes in neural processing of visual and/or somatosensory information when humans use a simple tool. Normal subjects were instructed to manipulate a small graspable object with a pair of tongs or with the fingers of their right or left hand. The only site activated during manipulation with the tool, compared with the fingers, with the right hand was the lateral edge of the right intraparietal sulcus (IPS). During manipulation using the left hand with the tool, compared with using the fingers, an area in the middle part of the left IPS was activated. Areas in the contralateral hemisphere were activated during both the tool-use and the finger-use tasks compared to the control task, but there was no statistically significant difference between the tool-use and the finger-use tasks. Therefore, the results suggest that the ipsilateral posterior parietal cortex was recruited during the tool-use tasks to integrate visuosomatosensory information.

The Effect of Verbal Feedback on Motor Learning—A PET Study

The purpose of this study was to investigate brain mechanisms underlying feedback effects on motor learning. We measured human brain activity using positron emission tomography (PET) during length-of-line drawing tasks in the presence or absence of verbal feedback, i.e., information on the precision of motor performance. The average error in responses was significantly lower and the percentage of correct responses was significantly higher in the case of tasks with feedback than those in the absence of feedback. The contralateral sensorimotor, premotor, supplementary motor, the right prefrontal, bilateral parietal and temporal, and anterior cingulate cortices, and the left basal ganglia were activated during all the line-drawing tasks. The right lateral prefrontal and occipital cortices and the left basal ganglia exhibited marked increase in activity after learning. The right inferior parietal and the anterior cingulate cortices were activated in the presence of feedback which provided information on how the subjects should correct their performances. The results indicate that these brain areas may play an important role in representing knowledge of results during motor learning and that appropriate feedback may facilitate motor learning.

Direction of cross‐modal information transfer affects human brain activation: a PET study

The purpose of this study was to determine the functional organization of the human brain involved in cross‐modal discrimination between tactile and visual information. Regional cerebral blood flow was measured by positron emission tomography in nine right‐handed volunteers during four discrimination tasks; tactile–tactile (TT), tactile–visual (TV), visual–tactile (VT), and visual–visual (VV). The subjects were asked either to look at digital cylinders of different diameters or to grasp the digital cylinders with the thumb and index finger of the right hand using haptic interfaces. Compared with the motor control task in which the subjects looked at and grasped cylinders of the same diameter, the right lateral prefrontal cortex and the right inferior parietal lobule were activated in all the four discrimination tasks. In addition, the dorsal premotor cortex, the ventral premotor cortex, and the inferior temporal cortex of the right hemisphere were activated during VT but not during TV. Our results suggest that the human brain mechanisms underlying cross‐modal discrimination have two different pathways depending on the temporal order in which stimuli are presented.

The European computerised human brain database

J. Fredriksson*-f, P.E. Roland*, P. Svenssont, K. Amunt&Q~, C. Cavada#, R Ha&, A. Coweyll, F. Crivetlo**, S. t&y&, 6. tt, B* **, D. Pep+weR

Four dimensions in the state of memory and emotion concerned with a person: Factor analysis using subject's self evaluation and PET

A. Schleicher

Anatomy and transmitter receptors of the supplementary motor areas in the human and nonhuman primate brain

, T. Schomam~, M. Seppa’, H. Uylings