What's in a name? The trail of the "vacuous chewing movement" model of tardive dyskinesia
Robert B. GLASSMAN
By the 1970s it had become evident that although neuroleptics enabled schizophrenic patients to lead more normal lives, chronic use of these drugs led to an irreversible side effect, usually characterized by spontaneous movements of the jaw, lips, and tongue. Responding to an opportunity for funding, I began research in this area. After reviewing much literature on schizophrenia and tardive dyskinesia, I suggested a “three echelon” theoretical model, which viewed symptoms of schizophrenia as subcortical release phenomena, resulting from weakened frontal cortical inhibition; the same model suggested that tardive dyskinesia itself was also a release phenomenon - of deeper subcortical regions - which emerged because higher subcortical levels were chronically enervated by antidopaminergic drugs (Glassman, R. B., A neural systems theory of schizophrenia and tardive dyskinesia, Behavioral Science, 21:274-288, 1976). This hypothesis appeared to be confirmed by an experiment in which rats having frontal cortical ablations, plus chronic administration of a neuroleptic, showed increased incidence of “vacuous chewing movements” (Glassman, R. B. & Glassman, H. N. Oral dyskinesia in brain-damaged rats withdrawn from a neuroleptic: Implication for models of tardive dyskinesia. Psychopharmacology. 69:19-25, 1980). Although the release phenomenon hypothesis got a lukewarm reception, the behavioral measure proved fertile. A PsycINFO search turned up 82 papers since 1980 that have used the term “vacuous chewing.” Of these, six cite our 1980 paper. A citation index search (I thank librarian Nancy Sosna Bohm) yielded 56 citations of the 1980 paper. Of these, six overlap with the PsycINFO search; 11 others of this 56 use the term “vacuous jaw movements” in the title; nine of those have an author in common.
Session V. Movement Disorders
Pavia, Italy, 2006