Electrophysiological study of blink reflex in humans: differences in mental and supraorbital nerves.

In order to find an explanation for the discrepancy between previous reports on the consistency of the blink reflex response with stimulation of the mental nerve, the habituation of the blink reflex was studied with stimulation of the supraorbital and mental nerves in 14 healthy adults. A series of eight electrical stimuli was delivered to the distributions of the nerves on each side at frequency rates of 1.0, 0.5, 0.2 and 0.1 Hz. The latencies and peak-to-peak amplitudes of the ipsilateral late blink reflex components (R2i) were measured. The habituation phenomenon was analysed by means of multivariate analysis of the amplitudes, the nerve and frequency effects were determined by means of a repeated measures analysis of variance model. The blink reflex showed more pronounced amplitude attenuation of the consecutive responses with stimulation of the mental than the supraorbital nerve at rates of 0.5 and 0.2 Hz, and marginally so also at 0.1 Hz. For the supraorbital nerve, habituation could be demonstrated with stimulation frequencies of 1.0 and 0.5 Hz, while for the mental nerve a statistically significant habituation phenomenon was found even with the lowest repetition rate of 0.1 Hz. The greater tendency of the mental nerve blink reflex to habituate is obviously one reason why it has previously sometimes been considered too inconsistent to be useful in clinical practice. For the recording of the supraorbital nerve blink reflex, a 10 s interval between stimuli is adequate, whereas longer interstimulus intervals may have to be adopted to obtain consistent blink reflex responses with stimulation of the mental nerve.