Presentation of a remote target influences visual responses of rabbit lateral geniculate cells

The described investigations analyze the influence of presenting a circumscribed target outside the limits of the classical receptive field (CRF) on the responses of lateral geniculate cells in rabbits. Animals were prepared for single cell recordings in acute experiments in the usual fashion. Cells were stimulated with a light-emitting diode (LED) positioned in the CRF and a second stimulus (S2) presented outside the field. The latter stimulus does not modify the spontaneous firing of the neuron when presented in isolation. S2 is either stationary or moving over small distances (total excursion is 3.5 degrees of arc). A moving S2 increases or decreases the responses to the LED by a greater magnitude than a stationary S2. Significantly, in 80 percent of direction-biased cells, centripetal movement of S2, that is, movement toward the receptive field, affected the neuronal discharge if it coincided with the preferred direction of the unit. These results suggest that the introduction of a remote stimulus modifies the responses of geniculate cells in rabbits.