Temporal modulation of the background affects the sensitization response of X- and Y-cells in the dLGN of cat.

ABSTRACT

The responses of X- and Y-cells to a small flashing test probe modulated at 2 Hz were measured as a function of the diameter of a concentric circular background. The background was either a static homogeneous disk, a flickered homogeneous disk, a static radially-vaned disk, or a rotating vaned disk, all of equivalent space- and time-averaged luminance. Variation of background diameter produced systematic changes in response that reflected general X- and Y-cell receptive field differences. Initial increases in background diameter decrease the response to the test probe ("desensitization") of both X- and Y-cells to a minimum level at a diameter that approximates the size of the receptive field center. Further increases in the background diameter result in an increase of the response to the test probe ("sensitization") that is very large for X-cells and much less for Y-cells. Temporal modulation of the background does not alter the desensitization of X- or Y-cells, but strongly reduces the sensitization of X-cells. Temporal modulation of the background by flicker and by motion produced equivalent effects. These results are compared to similar human psychophysical tests used clinically. Implications concerning the mediation of psychophysical sensitization are also considered.