SUMMATION AND DIVISION BY NEURONS IN PRIMATE VISUAL-CORTEX

Recordings from monkey primary visual cortex (V1) were used to test a model for the visually driven responses of simple cells. According to the model, simple cells compute a linear sum of the responses of later al geniculate nucleus (LGN) neurons. In addition, each simple cell's l inear response is divided by the pooled activity of a large number of other simple cells. The cell membrane performs both operations; synapt ic currents are summed and then divided by the total membrane conducta nce. Current and conductance are decoupled (by a complementary arrange ment of excitation and inhibition) so that current depends only on the LGN inputs and conductance depends only on the cortical inputs. Close d form expressions were derived for fitting and interpreting physiolog ical data. The model accurately predicted responses to drifting gratin g stimuli of various contrasts, orientations, and spatiotemporal frequ encies.