Eye-Head Coordination and Lateral Canal Block in Squirrel Monkeys

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Abstract
Eye and head nystagmus during horizontal optokinetic stimulation was analyzed in squirrel monkeys. Slow phase speed of coupled head and eye nystagmus showed highly significant negative correlations in normal subjects; correlation coefficients were −0.81 at 60°/sec and −0.72 at 100°/sec stimuli. Bilateral lateral semicircular canal block resulted in a reduction of the negative correlation. The postoperative reduction of the correlation coefficient value ranged from 0.17–0.28 (significant at P<0.01 level) at 60°/sec stimulus and 0.06–0.13 (not significant) at 100°/sec stimulus. Gaze speed was calculated by summing slow phase speeds of coupled head and eye nystagmus. Mean error of gaze in normal subjects was 1.5% at 60°/sec stimulus and 7.8% at 100°/sec stimulus. Mean gaze speed showed an overshoot (8% at 60°/sec stimulus and 6.5% at 100°/sec stimulus) in the three to four weeks postoperative period; however, this subsided two to three months after the operation. Measurement of head-turning performance (in yaw plane) in humans may provide a clinically useful index for the assessment of certain types of vestibular function.