Audiogenic startle reflex in acute hemiplegia.

The generators of the audiogenic startle reflex (ASR) are located in the bulbopontine reticular formation. We studied the influence of acute vascular supratentorial lesions on ASR. Ten patients with hemiplegia due to hemispheric cerebral infarct were studied within 5 days of stroke onset. ASR and magnetic cortical stimulation were performed the same day. A muscle response to magnetic stimulation was not elicited over the plegic side in any patient. In four of seven patients, ASR was enhanced over the plegic side. We suggest that enhanced ASR is due to the loss of a predominantly inhibitory hemispheric drive on ASR generators.