Abstract
1. The firing frequency of 31 single fibers in the trochlear nerve of alert monkeys was related to eye movement. Monkeys were conditioned to finger press lighted buttons in order to produce a calibrated sequence of eye movements in the horizontal and vertical directions. 2. About 3 msec prior to and during a downward saccade, all units exhibited an intense burst in firing frequency. The average maximum burst frequency was about 400 spikes/sec. 3. Prior to and during an upward saccade, all units exhibited a marked decrease in firing rate. 4. If the downward deviation of the eye exceeded a certain minimum position (the threshold), all units exhibited a very regular tonic rate during the fixation pauses between saccades. The tonic firing frequency was linearly related to vertical eye position. Maximum tonic rates reached 200–300 spikes/sec. 5. The activity of simian trochlear fibers is very similar to the activity of neurons in the abducens and oculomotor nuclei. Therefore, one functional type of motoneuron which subserves saccadic, smooth pursuit and fixation eye movements exists in all of the oculomotor nuclei. Vergence movements were not investigated.
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