Figure 3. Drug-induced OKR-like responses in the absence of a moving visual stimulus.

(A) Eye movements in the absence of a moving visual stimulus before and after an i.p. injection of ketamine (8 mg/kg), memantine (23 mg/kg), or phencyclidine (4 mg/kg). Scale bar: 0.5 mm. (B) Spontaneous eye movements before (n = 29) and after (n = 30) i.p. memantine, with saccade amplitudes normalized and traces temporally aligned by the saccade, and the time constant (T_C) of the best-fitting exponential for each recording of eye position versus time for the 116 milliseconds immediately after the saccade. The inset shows a graphical definition of T_C as the time corresponding to a 63% change in eye position, following exponential kinetics. Horizontal bars represent the mean. (C) Automated identification of box-car (black) versus OKR-like (red) spontaneous eye movements in 2 thirteen-second recordings, with or without i.p. phencyclidine. For each recording, the timing and polarity of the fast components were scored (central quantized trace), and then each saccade was categorized as box-car or OKR-like (bottom quantized trace). Scale bar: 1 mm. (D) Total (left), box-car–shaped (center), and OKR-like (right) saccades during a 10-minute recording obtained before (black) or after (red) the indicated drug. M, memantine; K, ketamine; P, phencyclidine. (E) Distribution of time intervals between adjacent fast components before versus after drug administration. (F) Clustering of saccade polarity: the number of adjacent saccades of the same polarity within a 10-minute interval before versus after drug administration. Blue lines show the calculated distribution of adjacent saccades of the same polarity for a matched number of saccades divided equally into positive and negative polarities and randomly ordered in time. For each drug, the data shown are from a single representative mouse. Data in B are presented as the mean ± standard deviation.