Responses to moving texture patterns of cells in the striate-recipient zone of the cat's lateral posterior-pulvinar complex.

Abstract

We have studied the response properties of cells in the lateral part of the lateral posterior nucleus or striate-recipient zone (LPl) of the lateral posterior nucleus-pulvinar complex to the motion of textured patterns [visual noise]. Our purpose was to determine basic noise response characteristics and to compare these properties to that of cells in area 17 known to project to the LPl. Practically all LPl cells (87%) responded to the motion of visual noise. The evoked discharges were either sustained or characterized by several bursts. On average, as found in cortex, LPl neurons were more broadly tuned for the direction of noise than that of gratings (bandwidths of 49 and 36 degrees, respectively; t-test, P < 0.005). Noise tuning function in LPl was comparable to that found in cortex (mean of 48 degrees). One third of the LPl units did not exhibit any preferences for drift direction of noise. Such cells were virtually not encountered in the striate cortex. This group of LPl cells was generally not tuned for grating direction. For practically all LPl cells, responses to noise varied as a function of drift velocity. The mean optimal velocity was 27.5 degrees/s with mean bandwidth of 2.5 octaves. LPl cells were sensitive to a broader range of velocities than complex cells in area 17. The results of the present study showed that visual noise is an appropriate stimulus for studying motion sensitivity of cells in the LPl. It also revealed that the noise response properties, such as direction and velocity tuning functions, are very similar to those reported in the striate cortex. The exact contribution of area 17 in the visual noise responsiveness of LPl cells remains to be determined. This study provides additional evidence that the lateral posterior nucleus-pulvinar complex may be involved in many aspects of visual processing.