Unilateral reduction of the early and late blink reflex component in hemiparkinson syndrome

Electrically evoked blink reflexes were recorded in 10 patients with unilateral tremor and/or rigor, mostly diagnosed as hemiparkinson syndrome. Five of the patients could be investigated before and after stereotaxic thalamo-subthalamotomy. The EMG activity of the early and late components was quantified by means of averaging and integrations techniques. In addition, the latencies of the reflex components were determined. The major finding was a unilateral decrease of the EMG activity of both the early and late components confined to the clinically affected side. This pattern points to a lowered state of excitability of neurons in or close to the facial nucleus, probably due to a dysfunction of contralateral EPMS structures. A loss of facilitatory influences from EPMS centers, e.g. the nigro-striatal system, on brain stem neurons in the area of the facial nucleus appears most probable. The latencies of the early and late components were mostly normal. After stereotaxic surgery, the BR activity was decreased bilaterally. The difference between the affected and unaffected sides, however, was nearly unchanged. At present an unspecific postoperative effect cannot be excluded.