Auditory evoked potentials and response to lithium prophylaxis

Auditory evoked potentials were recorded in 28 euthymic patients with affective psychosis who had received lithium prophylaxis for at least 5 years. Binaural clicks at 4 intensities were presented in randomized order via headphones. Potentials were recorded from Cz, C3, and C4 referenced to linked mastoid electrodes. N1-P2 amplitudes, N1 and P2 latencies, and the slope of the amplitude/stimulus intensity function (ASF) were determined in each patient. The patients were divided into responders and nonresponders on the basis of whether or not they had been hospitalized for treatment of relapses during the last 5 years of lithium prophylaxis. The ASF was steeper for all leads in responders than in nonresponders. In addition, N1 latencies were shorter for all leads in responders than in nonresponders. Age played a role in the differences observed between responders and nonresponders for ASF, but not for N1 latencies.