Second-generation antipsychotics (SGA) are thought to have a more favorable impact on neurocognitive functions with respect to first-generation antipsychotics (FGAs). Event-related potentials (ERPs) represent valuable tools in the assessment of cognitive effects of psychotropic drugs; however, few ERP studies investigated antipsychotic drug effects on neurocognition in human subjects.

The present ERP, double-blind, cross-over study was carried out in 12 male healthy subjects to investigate the effects of a single oral dose of haloperidol, placebo or risperidone on effortful and automatic allocation of attentional resources to auditory stimuli.

ERPs were recorded from 30 unipolar leads (0.5-70 Hz bandpass, 256 Hz sampling rate), during a three-tone oddball task in which target, standard and rare-nontarget tones were randomly presented. Subjects had to press a button when hearing a target tone, while ignoring both standard and rare-nontarget stimuli.

P3 for target (P3b) and rare-nontarget stimuli (P3a) were identified at Cz and Pz leads. Amplitude maps at peak latency were then compared across conditions. If a significant drug effect was obtained, changes in the cortical sources of P3 were analyzed using Low-Resolution Electromagnetic Tomography (LORETA).

No change was observed for P3b. P3a amplitude was increased by risperidone, at midline and right centro-parietal regions, but not by haloperidol. No change was observed in P3a cortical generators.

P3a, an index of the automatic allocation of attentional resources, is increased only by risperidone, suggesting a favorable effect of this SGA on orienting processes.