A study of contingent negative variation and post-imperative negative variation: search for state and trait electrophysiological markers in schizophrenia.

OBJECTIVE To compare event-related potential measures, contingent negative variation and post-imperative negative variation in drug-naïve or drug-free schizophrenic patients and normal healthy controls, and to study the effect of antipsychotic medication on the above measures. METHODS A hospital-based prospective study was conducted at Central Institute of Psychiatry, Ranchi, India. The sample constituted 31 drug-naïve or drug-free patients with schizophrenia and 31 normal healthy individuals, matched for age and gender. An S1-S2 paradigm was used, in which the warning stimulus (S1) was auditory and the target stimulus or imperative stimulus (S2) was visual. The early contingent negative variation was marked at 500 milliseconds after S1, and late contingent negative variation was marked as the negative wave just prior to S2. The post-imperative negative variation was measured as the continued negativity after S2. RESULTS Drug-naïve and drug-free patients significantly differed from the controls on amplitudes of early and late contingent negative variations, as well as on latency of late contingent negative variation. The rate for correct classification in 80% of cases (Wilks' lambda = 0.76) was observed in measuring amplitude of late contingent negative variation only. After exposure to antipsychotic drugs, the late contingent negative variation amplitude was found to normalise in the patient group. CONCLUSION The late contingent negative variation could be considered a state marker for schizophrenia.