Blink Reflex Evocation and EMG Recording

The subjects were examined in a comfortable supine position and instructed to keep their eyes gently closed. The EMG activity of the orbicularis oculi muscle was recorded by attaching surface electrodes to the subject's skin using a conductive electrode gel. The active electrodes were placed on the lower eyelids, the reference electrodes were placed 2 cm lateral to the outer canthi, and the grounding electrode was placed on the wrist of the left upper limb. Each blink reflex was evoked by electrical stimulation (constant current rectangular pulses with a stimulation duration of 0.2 ms) above the right supraorbital notch percutaneously. The stimulus intensity was 10 times the sensory threshold, defined as the minimum stimulation intensity at which the subject could perceive at least four of eight stimuli.