MONKEY P3 IN AN ODDBALL PARADIGM - PHARMACOLOGICAL SUPPORT FOR MULTIPLE NEURAL SOURCES

Two experiments examined the effects of the alpha-2 antagonist L657,74 3 on monkey electroencephalographic (EEG) and event-related potential (ERP) activity following auditory and visual stimuli. In the first exp eriment, EEG was recorded before and after the administration of a sal ine placebo or L657,743 (0.01, 0.05 mg/kg IM). No drug effects occurre d on EEG spectral frequencies. In the second experiment, ERPs were rec orded during an 80- 10- 10 passive oddball paradigm. The paradigm cons isted of a repetitive tone as background, a different-pitch tone as th e auditory oddball, and a yellow rectangle as an infrequent visual sti mulus. Waveforms were collected before and after the administration of placebo or drug (0.01, 0.03, 0.05 mg/kg IM). Both auditory oddball an d visual stimuli elicited large P34-like potentials with different dis tributions, suggesting different sources. However, their magnitudes we re similarly reduced by drug administration. These effects were signif icant at parietal but unchanged at other sites. The data support the h ypothesis that norepinephrine is a modulatory neurotransmitter common to auditory and visual P3s in parietal areas. On the other hand, midli ne and temporal P3s are unaffected by manipulations of noradrenergic a ctivity, supporting the existence of two independent P3 sources.