Effects of patterned backgrounds on responses of lateral geniculate neurons in cat.

In the lateral geniculate nucleus (LGN) of paralyzed cats under urethane anaesthesia, an extensive disinhibitory region (DIR) outside the inhibitory surround of the receptive field (RF) was found in both sustained and transient cells. Its extent is comparable to that of McIlwain's periphery effect (1964). The responses to a light spot, flashed into different parts of the RF center, were used to assess the effect of different background patterns, located over the DIR, on responsiveness and receptive field organization. A straight line background cutting across the RF center led to a marked shrinkage in RF size and to a suppression of the center response. In sustained cells, these influences were not due to the light flux of the background, but were mainly due to the spatial property of the line itself. This was demonstrated by comparing the effect of a straight line background with that of a zigzag line or of distributed dots. The light flux for the different patterns and their spatial weighting was the same, so that they differed from each other solely in their form. A straight line background elicited much stronger suppression of the center response and more marked shrinkage of the RF than if the component dots are dispersed over a wider area, but keeping the radial distances of the individual dots from the RF-center constant. The data suggest that the dispersion of the component dots in different backgrounds plays an important role as response amplitude and RF diameter increase proportional to the dispersive area of the background patterns. For transient cells, all backgrounds used showed similar effects on center responses and RF diameter, indicating that for them it was the light flux of the backgrounds rather than their spatial property that caused the effects.