Cortical slow potential shifts in tardive dyskinesia.

1. Slow cortical potential shifts such as the late terminal E-wave component of the CNV appear to be determined mainly by the level of motor preparation and as such it was employed to investigate the degree of cortical involvement in schizophrenics exhibiting abnormal motor phenomena induced by prolonged treatment with neuroleptics. 2. The basic experimental task was a constant foreperiod warned reaction time task consisting of a brief warning tone (S1) followed 4 sec later by a light, the imperative stimulus (S2), upon which the subject was instructed to release a response key. The task was presented twice, in a randomized order, under neutral and fast set instructions, to tardive (TD) and non-tardive dyskinesia (NTD) groups. 3. Computer EEG analysis identified and analysed on early O-wave measured as the average amplitude 500-1000 msec post S1, and the latter E-wave measured as the average amplitude 500 msec prior to S2. Two additional epochs of PINV activity were also analysed. 4. The results indicated that the TD group exhibited significantly larger PINV activity, but unlike NTD patients, the TD group failed to exhibit any significant increases in E-wave amplitude concommitant with improved behavioral reaction times. The results are discussed in relation to a disinhibitory theory of tardive dyskinesia.