Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
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BCCN AG-Seminar

Tuesday, 07.02.2006 16 c.t.

Impact of interhemispheric connections on orientation preference in areas 17 and 18 of the ferret

by Dr. Kerstin Schmidt
from Department of Neurophysiology, Max-Planck-Institute for Brain Research, Frankfurt

Contact person: Fred Wolf

Location

Seminarraum Haus 2, 4. Stock (Bunsenstr.)

Abstract

Visual callosal connections extend between topographically corresponding regions in both hemispheres mainly representing the midline of the visual field (vertical meridian, VM). They are thought to extend preferentially between neurons of similar response properties and to integrate information from the two hemifields close to the VM. In ferrets as in other carnivores, the callosal zone expands extensively from the 17/18 border and covers a larger field than only the VM representation. It probably overlaps with a zone of bilateral representation of the central visual field in the two hemispheres. In order to investigate the functional impact of visual callosal connections on neuronal responses in areas 17 and 18 of the ferret we reversibly deactivated visual areas 17, 18 and 19 in one hemisphere by the cryoloop technique. We chose loop temperatures (2°) known to deactivate all cortical layers because callosal connections in the ferret emerge from both, infragranular and supragranular layers. Before, during and after deactivation orientation preference maps in contralateral areas 17 and 18 were obtained by optical imaging of intrinsic signals while stimulating binocularly with moving iso-oriented whole-field gratings centered on the midline and extending up to 20° in both hemifields. In a separate series of experiments, multiunit activity from 15 parallel recording sites was recorded during the manipulation. Deactivation slightly degraded orientation maps and unit responses in areas 17 and 18. Both the absolute level of activity as well as the specificity of responses were decreased in the absence of interhemispheric input by 13% (average of 8 ferrets). Thereby, the structure of the orientation maps was largely preserved. Especially close to the areal border domains preferring horizontal contours were more affected than other orientation domains. Our results suggest that callosal connections contribute to the strength and specificity of the orientation response in large parts of areas 17 and 18 representing the central visual field. Thereby, horizontal orientation domains predominantly benefit from the intact callosal connection. We suggest that callosal connections between neurons preferring horizontal contours are more frequent. These findings are compatible with callosal connections contributing to reconstruct complex visual stimuli which cross the boundaries of the visual hemifields.

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