Individual differences in average evoked responses to d- and l-amphetamine with and without lithium carbonate in depressed patients.

Visual average evoked responses (AERs) to four intensities of light were studied in hospitalized depressed patients receiving placebo, d-amphetamine, l-amphetamine, lithium and d- and l-amphetamine combined with lithium. For the assessment of the subjective effects of the drugs, the patients completed a 34-item mood and behavior self-rating scale. AER responses to repeated doses of the amphetamines were consistent within the same individual but varied greatly between different individuals. For the patient group considered as a whole, only minor AER changes occurred in response to either d- or l-amphetamine; nonetheless, these minor changes were attenuated by lithium co-administration. There were indications, however, that AER baseline measures could be used as predictors of change in self-rating due to both d- and l-amphetamine, as patients who had larger AER amplitudes on baseline also tended to have larger increases in activation ratings and reductions in depression ratings. The amount of increase in AER amplitude or amplitude/intensity slope seen with amphetamine was also significantly correlated with the amount of increase in activation or euphoria ratings with amphetamine administration. These effects were most prominent in the same P100 component that we have previously found to differentiate bipolar and unipolar depressed patient groups.