Electrophysiological (H-reflex) studies of patients with tardive dyskinesia.

The authors studied the H-reflex recovery curves of 31 schizophrenic patients with tardive dyskinesia in response to acute administrations of apomorphine, amphetamine, or physostigmine and compared them with curves of chronic schizophrenic patients without tardive dyskinesia and normal volunteers. Their most unexpected finding was the absence of an H-reflex in 9 of the 31 patients with tardive dyskinesia. They also found a relationship between severity of tardive dyskinesia and the value of the facilitatory peak Hchi: patients with more severe tardive dyskinesia symptoms had significantly higher values for Hchi.