Initiation of the optokinetic response (OKR) in mice.

To study the initial part of the mouse optokinetic response, OKR (approximately 500 ms from the onset of visual stimulus motion), we recorded the ocular response to a vertical sinusoidal grating moving at a constant velocity. We found that the magnitude of the response monotonically increased as the stimulus contrast increased. The response showed a narrow band-pass property for the spatiotemporal frequency, with the largest sustained response observed at 0.125 cycle/deg and 1.5 Hz. We also found that temporal frequencies higher than 1.5 Hz elicited transient increase in the eye velocity, but weak or no sustained eye movements. Thus the initial OKR in mice is characterized by the spatiotemporal frequency of the visual stimuli. Our results suggest that the initial OKR contains two components: a transient that diminishes within approximately 200 ms, and a tonic that is maintained for more than 400 ms, and that the initial part of the OKR in mice is an appropriate measurement parameter for studies of the visual and motor systems, like ocular following response (OFR) in primates.