Monkey P3 in an "oddball" paradigm: pharmacological support for multiple neural sources.

Two experiments examined the effects of the alpha-2 antagonist L657,743 on monkey electroencephalographic (EEG) and event-related potential (ERP) activity following auditory and visual stimuli. In the first experiment, EEG was recorded before and after the administration of a saline placebo or L657,743 (0.01, 0.05 mg/kg IM). No drug effects occurred on EEG spectral frequencies. In the second experiment, ERPs were recorded during an 80-10-10 passive oddball paradigm. The paradigm consisted of a repetitive tone as background, a different-pitch tone as the auditory oddball, and a yellow rectangle as an infrequent visual stimulus. Waveforms were collected before and after the administration of placebo or drug (0.01, 0.03, 0.05 mg/kg IM). Both auditory oddball and visual stimuli elicited large P3-like potentials with different distributions, suggesting different sources. However, their magnitudes were similarly reduced by drug administration. These effects were significant at parietal but unchanged at other sites. The data support the hypothesis that norepinephrine is a modulatory neurotransmitter common to auditory and visual P3s in parietal areas. On the other hand, midline and temporal P3s are unaffected by manipulations of noradrenergic activity, supporting the existence of two independent P3 sources.