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

Wednesday, 08.02.2006 14 c.t.

Stimulus dependent redistribution of gamma oscillation frequency in V1

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

Contact person: Fred Wolf


Seminarraum Haus 2, 4. Stock (Bunsenstr.)


Gamma activity has been associated with various integrative processes in the visual system. Numerous studies in anesthetized animals have shown a conspicuous increase in power for the gamma frequency band (30 to 60 Hz) in response to visual stimuli. Recently, these observations were extended to behavioral studies, which specifically addressed the role of gamma activity in cognitive processes demanding selective attention. In most of these investigations drifting gratings have been chosen as stimulus. A common finding was the dependence of gamma oscillations on stimulus properties, such as contrast, direction of movement, spatial frequency and coherence. Stimuli, which activate a large number of cells sharing similar properties, generally induce strong gamma responses. Here we used a second moving grating superimposed on the first one (plaids) in order to simultaneously activate cell populations with different tuning properties. We were able to confirm previous findings, which showed strong gamma activity in responses to moving gratings. Synchronous oscillatory responses were seen both at the single cell and population levels. Synchronization strength was stable during the whole epoch of stimulation and occasionally increased along the course of the trial. A clear disruption of synchronous oscillatory patterns was observed by adding a second grating (plaids condition). This effect was specific for the gamma band, as seen by correlation and spectral analysis of the local field potential. Interestingly, synchronization was not recovered by changing the superimposed gratings into a single object (pattern motion condition). The differences observed in gamma activity for the various conditions occurred without a significant difference in firing rates. A possible explanation for our results may be found in the patterns of intra-cortical connections in V1, since cells of similar properties are preferentially connected. Single gratings are capable of inducing strong cooperative interactions among a homogeneous population of cells while the plaid leads to competition. Further studies addressing the role of attention and expectation on cooperative interactions are necessary to clarify these issues.

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