Exteroceptive reflexes in dystonia: a study of the recovery cycle of the R2 component of the blink reflex and of the exteroceptive suppression of the contracting sternocleidomastoid muscle in blepharospasm and torticollis

Abstract

The recovery cycle of the R2 component of the blink reflex and the exteroceptive suppression of EMG activity in the contracting sternocleidomastoid muscle produced by electrical stimulation of the supraorbital nerve were studied in normal subjects and in patients with either blepharospasm or torticollis. The latencies of the reflexes were normal, suggesting that the neural structures that mediated them were intact. However, the recovery of the R2 component of the blink reflex was enhanced in patients with either blepharospasm or torticollis. Also, the size of the exteroceptive suppression of the sternocleidomastoid muscle was reduced in both groups of patients. Our results are indicative of abnormalities of interneurons mediating exteroceptive reflexes in patients with craniocervical dystonia that are not restricted to the systems controlling the muscle involved in the dystonia.