Eyelid responses evoked by microstimulation of the PIN. A, Orbicularis oculi electromyography (OO EMG) and eyelid response to two electrical pulses (50 μsec; 50 μA) applied to the ipsilateral PIN. Note the small amplitude of the evoked eyelid response. B, OO EMG and eyelid responses evoked by a train (20 Hz) of electrical pulses applied to the PIN. C, Trains of stimuli (20 Hz for 1 sec) applied to the PIN had no long-lasting effects (ANOVA) on eyelid responses (mean amplitude ± SEM; n = 10) evoked by single pulses applied to the same site. The single pulses were applied at 1 Hz, and the train was presented twice as indicated (arrows). St, Electrical stimulation.