Abstract View

TEMPORAL DYNAMICS OF ORIENTATION SELECTIVITY DEPENDS ON LOCATION IN THE ORIENTATION PREFERENCE MAP IN CAT V1. J.Schummers1,2*; J.Mariño1,2; M.Sur1,2 1. Brain & Cog Sci, 2. Picower Ctr. for Learning and Memory, Massachusetts Inst. Tech, Cambridge, MA, USA Within the orientation preference map in V1, the orientation composition of the local connections impinging on any point in the map depends strongly on the local orientation gradient at that particular location. We have previously shown that the subthreshold synaptic inputs to individual neurons reflect the distribution of orientations in the local cortical patch surrounding them. However, the spike outputs do not depend on location in the map, indicating some form of non-linear input-output transformation. We have examined the timecourse of responses to flashed stimuli to determine whether the dynamics of responses might shed some light on the integration of inputs. Using reverse-correlation analysis of spike responses to rapidly changing orientations, we have compared the tuning curves at different times relative to stimulus onset between neurons located near and far from pinwheel centers. We find that the earliest spike responses in pinwheel neurons are less selective than in orientation domain neurons. Near pinwheel centers, there is an initial increase in response to all orientations, relative to a blank stimulus, which is subsequently sculpted by suppression at non-optimal orientations. At later timepoints, there is no difference in the tuning curves of pinwheel and orientation domain neurons, as in the steady state responses to drifting gratings. We have also made whole cell recordings of responses to flashed gratings. Preliminary analysis is consistent with several aspects of the extracellular reverse-correlation analysis. Overall, our results indicate that the global and/or orientation specific suppressive mechanisms may play an important role in shaping the input-output transformation performed by V1 neurons. Support Contributed By: EY07023 (MS), MECD (JM) and HHMI (JS) Citation: J. Schummers, J. Mario, M. Sur. TEMPORAL DYNAMICS OF ORIENTATION SELECTIVITY DEPENDS ON LOCATION IN THE ORIENTATION PREFERENCE MAP IN CAT V1. Program No. 818.6. 2003 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience, 2003. Online.