Blink reflex studies in patients with Parkinsonism before and during therapy.

Electrophysiological analysis of the blink reflex makes it possible to quantitate the reflex changes observed in pathology. The authors therefore propose a `habituation index' to be determined by recording the electromyographic reflex response during stimulation at controlled frequencies. Several populations of subjects were tested. It was confirmed that marked differences in blink reflex habituation exist between normals and patients with Parkinson's disease. It was also found that when patients with Parkinsonism were treated with the classical anticholinergic drugs their habituation index remained virtually unchanged. However, treatment with either l-dopa or amantadine caused a rise in the index in almost all patients tested. On the basis of these findings it is suggested that these two new drugs have a highly similar mechanism of action.