The dynamics of primate M retinal ganglion cells
The retinal ganglion cells (RGCs) of the primate form at least two classes—M and P—that differ fundamentally in their functional properties. M cells have temporal-frequency response characteristics distinct from P cells (Benardete et al., 1992; Lee et al., 1994). In this paper, we elaborate on the temporal-frequency responses of M cells and focus in detail on the contrast gain control (Shapley & Victor, 1979a,b). Earlier data showed that the temporal-frequency response of M cells is altered by the level of stimulus contrast (Benardete et al., 1992). Higher contrast shifts the peak of the frequency-response curve to higher temporal frequency and produces a phase advance. In this paper, by fitting the data to a linear filter model, the effect of contrast on the temporal-frequency response is subsumed into a change in a single parameter in the model. Furthermore, the model fits are used to predict the response of M cells to steps of contrast, and these predictions demonstrate the dynamic effect of contrast on the M cells' response. We also present new data concerning the spatial organization of the contrast gain control in the primate and show that the signal that controls the contrast gain must come from a broadly distributed network of small subunits in the surround of the M-cell receptive field.(Received January 9 1998)
(Accepted September 2 1998)
Key Words: Primate; Retina; M cell; Dynamics; Contrast gain control.
c1 Correspondence and reprint requests to: Ethan A. Benardete, Department of Neurosurgery, New York University Medical Center, 550 First Avenue, New York, NY 10016.
p1 Current address: Department of Neurosurgery, New York University Medical Center, 550 First Avenue, New York, NY 10016, USA.
p2 Permanent address: Department of Ophthalmology, Mount Sinai Medical Center, New York, NY 10029, USA.