Electrically induced blink reflex and clinical blinking ability in patients with amyotrophic lateral sclerosis

A study of the electrically induced blink reflex was performed on 17 patients with amyotrophic lateral sclerosis (ALS), graded according to the voluntary and reflexive blinking ability. In the early stage, delay of bilateral R2 latencies, decrease of bilateral R2 amplitudes and disappearance of the contralateral R2 component occurred. Then, the ipsilateral R2 component vanished when the voluntary blinking was incomplete. In cases with the remaining R2 component, the recovery curves of R2 amplitude revealed the weakened influence of the central nervous system to the interneurons that constructed the R2 component. In highly impaired patients who had lost the reflexive blinking ability, the R1 component had disappeared. Electrically induced blink reflex is useful in assessing the degree of disability in the upper facial muscles.