Pretectal neurons responding to slow wide-field retinal motion: Could they compensate for slow drift during fixation?

The visual response properties are described of a group of retinal slip neurons in the wallaby pretectum, referred to as slow cells. Their responses to motion are direction-selective: tempero-nasal and naso-temporal motion over the contralateral eye increase and decrease, respectively, the firing rate relative to the spontaneous level. Slow cells are maximally sensitive to image velocities from 0.08 to 10°/s. The present study focuses on slow cells that are maximally sensitive to image velocities below 1°/s. An interesting characteristic of 82% of slow cells is that once motion stops, the firing rate exhibits a same-sign after-response. This is characterized by a slow exponential return from the firing rate during motion to the spontaneous rate. The time constants of the after-responses are independent of the temporal frequency, velocity, duration and direction of the motion stimulus. It is proposed that the neurons may assist the stabilization of eye position during fixation.