VESTIBULO-COLLIC REFLEX IN TOPOLOGICALLY DEFINED BRAIN-STEM LESIONS

Stimulation of the ear by loud elicits evokes a potential which can be averaged out of the EMG-activity from contracted sternocleidomastoid muscle. This phenomenon has been called vestibulo-collic reflex becaus e of a presumed disynaptic pathway from the vestibular organ via the v estibular nuclei to the motoneurons of cervical muscles. In order to t est this suggested pathway, we examined the vestibulo-collic reflex in 20 healthy volunteers and seven patients with topologically defined l esions of the brain stem (four patients with Wallenberg's syndrome of the dorsolateral medulla, one patient with a lesion in mesencephalon a nd two patients with tumors in the cerebello-pontine angle). Clicks we re delivered unilaterally via a pair of headphones. EMC activity was c ollected over 100 ms by surface electrodes placed on sternocleidomasto id belly and averaged. Muscle was maintained in tonic contraction duri ng the examination by elevation of the head. In the healthy subjects, a biphasic potential with initial positive deflection and short latenc y could be recorded on the side of the stimulation (fig. 2). In the tw o patients with tumors in the cerebello-pontine-angle and in two patie nts with Wallenberg's syndrome, the potential was abolished on the aff ected side (fig. 4). One of these patients, who showed a loss of the p otential four days after the stroke, was examined a second time fiftee n days later, and now the reflex had reappeared. In the other two pati ents with Wallenberg's syndrome, the reflex was normal. But in these t wo persons, the ischemic lesion was already older (>10 days). Our resu lts support the suggested pathway of the vestibulocollic reflex from t he vestibular nuclei to the motoneurons of the sternocleidomastoid mus cle in the dorsolateral medulla.