[The electrophysiological approach to tardive dyskinesias]

Electrological study of TD is of value on two counts: it facilitates diagnosis in cases where the origin of the dyskinesia is not known, it enables objective monitoring of therapeutic studies. TD electromyographic recordings are highly specific. The recording shows: either, continuous activity of irregular amplitude corresponding to that which is called "tardive dystonia" in a clinical context, or, discontinuous irregular activity sometimes grouped into bursts of activity of relatively long duration, with a rhythm of 0.5 to 2 Hz during the temporal sequences, which are of variable duration. This type of activity is the same as that found in movements induced by L-dopa (L-dopa IM). In both cases, these involuntary movements only occur after several months' or years' treatment. They predominate in the oro-facial region. However, reactions to various pharmacological agents are not identical. While activity is decreased by neuroleptics and increased by L-dopa, anticholinergics have no effect on L-dopa IM whereas they exacerbate TD. GABA decreases TD but is ineffective against L-dopa IM. The reaction of these movements to L-dopa and neuroleptics, suggests that both reflect hypersensitivity to dopamine. Their different reactions to GABA lead one to suppose that GABA modulation of the dopaminergic system is defective in TD.