Intensity dependence of auditory evoked potentials and clinical response to prophylactic lithium medication: a replication study.

A predictor of clinical response to prophylactic lithium treatment in affective psychoses would be of considerable importance. In a pilot study, responders to prophylactic lithium medication, as compared with nonresponders, were characterized by a steeper slope of the amplitude/stimulus-intensity function (ASF slope) of the N1/P2 component of the auditory evoked potential. We tried to replicate this finding in 34 stabilized outpatients with affective illness who had been treated with lithium for at least 3 years. As in the pilot study, responders were again characterized by steeper ASF slopes than nonresponders. Since a steep ASF slope seems to indicate low central serotonergic function, it is speculated that a steep ASF slope characterizes those patients with a serotonin deficit who respond to serotonin agonists like lithium.