8th International Conference on
Functional Mapping of the Human Brain
June 2 - 6,2002, Sendai, JAPAN
Presidential Symposium
Cyto- and receptorarchitectonics of the human parietal cortex
Karl Zilles
Institute of Medicine, Research Center Juerich, D-52425 Juerich; and C.&O. Vogt-Institute of Brain Research, University of Duesseldorf, D-40001 Duesseldorf
Cyto- and myeloarchitectonic maps of the human parietal cortex have been published since the beginning of the last century. However, the parietal lobe remained an uncharted region, since these findings failed to explain the much greater areal differentiation, especially in the posterior parietal cortex, which has been revealed by functional imaging studies (e.g., Bremmer et al. 2001; Fink et al. 2000).
Since a complete architectonic map of the human parietal cortex still remains a task for the future, this talk will
- revisit the practically forgotten myelo- and cytoarchitectonic studies by Vogt (1911), Gerhardt (1940) and Batsch (1956), and
- present new data indicating the regional heterogeneity of transmitter receptor distributions (receptor architectonics) and laminar organization (cytoarchitectonics) in the human parietal lobe.
Architectonical and imaging data are displayed in a common spatial reference system. The intersubject variability in size and position (relative to macroscopical landmarks) of parietal areas is reflected by probability maps of the cortical areas. Thus, results from activation studies can be directly correlated with cytoarchitectonic maps. This approach provides a detailed insight into the anatomical structure of activated foci.
The analysis of the regional and laminar distribution of numerous different receptors of all classical transmitter systems provides a new tool for the neurochemical characterization of the parietal areas, especially if compared to primary and higher unimodal sensory cortices, motor areas and other association cortices. It was found that different functional systems within the parietal cortex differ by their receptor fingerprints (simultaneous presentation of areal specific densities of numerous transmitter receptors by polar coordinate plots), which demonstrate the structural and functional heterogeneity of the human parietal cortex (Zilles and Palomero-Gallagher 2001).
Batsch, E.-G. 1956. Die myeloarchitektonische Untergliederung des Isocortex parietalis beim Menschen. J. Hirnforsch. 2: 225-258.
Bremmer, F., Schlack, A., Shah, N.J., Zafiris, O., Kubischik, M., Hoffmann, K.-P., Zilles, K., and Fink, G.R. 2001. Polymodal motion processing in posterior parietal and premotor cortex: a human fMRI study strongly implies equivalencies between humans and monkeys. Neuron 29: 287-296.
Fink, G.R., Marshall, J.C., Shah, N.J., Weiss, P.H., Halligan, P.W., Grosse-Ruyken, M., Ziemons, K., Zilles, K., and Freund, H.-J. 2000. Line bisection judgements implicate right parietal cortex and cerebellum as assessed by fMRI. Neurology 54: 1324-1331.
Gerhardt, E. 1940. Die Cytoarchitektonik des Isocortex parietalis beim Menschen. J. Psychol. Neurol. 49: 367-419.
Vogt, O. 1911. Die Myeloarchitektonik des Isocortex parietalis. J. Psychol. Neurol. 18: 107-118.
Zilles, K., and Palomero-Gallagher, N. 2001. Cyto-, myelo- and receptor architectonics of the human parietal cortex. NeuroImage 14: 8-20.
Parietal Cortical Mechanisms for Spatial Navigation
Charles J. Duffy
University of Rochester, Rochester, NY, USA
Neurons in monkey extrastriate cortical area MST respond to optic flow stimuli that simulate the visual scene during observer self-movement. We presented optic flow stimuli during whole-body translational movement and found robust interactions between visual, vestibular and pursuit signals about heading direction. These signal interactions function to support the neuronal population representation of heading direction under various naturalistic conditions.
Combined optic flow and translational movement on a circular path revealed more complex self-movement signals in MST. Many neurons showed large differences in their heading responses depending on whether the animal had followed a clockwise or counterclockwise path to the preferred heading. Other neurons reversed their heading selectivity on clockwise and counterclockwise paths. These neurons responded best at a specific place in the room, regardless of the path taken to that place.
Our findings suggest that MST neurons combine multi-sensory cues about self-movement to represent heading direction based-on the most reliable cues that are available at that time. Signal interactions in MST may be the cortical foundation of the animalŽÕs spatial representation of its location in the environment and the neurophysiological basis of its using self-movement to update its internal representation of its position in the environment.
Neural basis of body image in the parietal cortex
Atsushi Iriki
Department of Physiology, School of Dentistry, Tokyo Medical and Dental University
Bimodal (somatosensory and visual) neurons in the monkey intra¡¡parietal cortex (where the hierarchical processing of somatosensory information adjoin the information on spatial vision processed along the dorsal stream) code the image of the self, which is subject to intentional modification. When trained to use a tool, it becomes an extension of the hand both physically and perceptually, resulting in alteration of the body image (the knowledge about the dimension, posture and movement of the arm in relation to the environmental space) in accordance with the characteristics of the tool at¡¡hand: We trained macaque monkeys to retrieve distant objects, beyond the limit of the reach of the innate arm, using a rake as a tool and neuronal activity was recorded in the anterior bank and the fundus of the intraparietal sulcus contralateral to the hand using a tool. There we found a large number of bimodal neurons which appeared to code the image of the hand by integrating somatosensory and visual information - these neurons have visual receptive fields which encompass their somatosensory receptive fields located at hand and forearm. During tool use, their visual receptive fields were altered to include the entire length of the rake. These use-dependent expansion occurred only when the monkeys held a tool and intended to use it as an extension of their hand. These findings may constitute the neural correlate formodification of the body schema as a basis of assimilation of the tool intoour own body. Also, we found that these neurons can also code the body-image projected onto the video monitor, perhaps corresponding to its "iconic" representation. During the course of training, behavioral analyses suggested that a novel mode of somatosensory-visual integration seemed to develop in order to organize adequate bodily movement to manipulate the tool, possibly subserved by reformation of the neural circuitry in which molecular genetic processes in the cortical area described above are involved. We are now extending these studies (by combining behavioral, electrophysiological, neuroanatomical, molecular biological, and positron emission tomography imaging techniques) to examine the cortical mechanisms subserving tool use in monkeys. When above described representations were further advanced, it would become totally free from physical constraints of the actual world to become a (pre-)symbolic one to represent evolutionary precursors of higher cognitive functions, and might eventually lead to evolution of human language or to the met aphysical thoughts. HOME
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