3006

Long-Range Spatial Organization Of The Receptive Fields Of Macaque V1 Neurons

Wednesday, May 08, 2002, 3:51 PM - 4:11 PM

J.Movshon. Center for Neural Science, New York University, New York, NY.

'The responses of V1 neurons have been reported to be facilitated in specific ways by targets outside the classically-mapped receptive field (RF); these effects have been linked to psychophysical long-range interactions. Using summation methods, we find that the excitatory RF is substantially larger than previously thought, because classical mapping techniques do not detect weak excitatory zones on the RF fringe. Outside the excitatory RF center, we find only inhibitory influences, which are strongest for stimuli that match the center in orientation and spatial scale. We account for our results and those of others by modeling the RF as a single excitatory profile overlapped by a larger zone of inhibition that modifies the gain of responses. The sensitivity of the center and surround are independently regulated by contrast and stimulation history. As a result, the summation of excitatory influences within the RF center varies, and can appear to be of large extent when surround sensitivity is low and the fringes of the RF center are unmasked. The dimensions of the RF center match the scale of horizontal intracortical connections in V1, suggesting that these connections do not support "long-range" interactions, but simply provide excitatory inputs that build the classical RF. The only "long-range" interactions evident within V1 RFs are inhibitory, and seem to be involved with the regulation of gain. Because facilitatory interactions supporting psychophysical long-range effects are not evident in V1 cells, these effects must in the main be mediated by areas outside V1 where neurons have larger RFs.
Co Authors: James R. Cavanaugh*, and Wyeth Bair. New York University* and HHMI.

 J. Movshon, None.