Human flash-VEP and quantitative EEG are independently affected by acute scopolamine

Scopolamine in acute intramuscular doses of 0.25-0.75 mg reduced the P2-N3 flash-VEP amplitude and, in the quantitative EEG, the 8.5-12.0 Hz power and total power in 8 healthy young male volunteers. The effects on flash-VEP and EEG total power were dose dependent and were evident 30 min and 90 min respectively after drug administration, regardless of dose. The reduction in 8.5-12.0 Hz power was limited to the 0.50 and 0.75 mg doses. No systematic effects on the pattern-VEP were observed. Possible interferences with flash- or pattern-VEP amplitude of the scopolamine-induced EEG changes were identified and removed by regression analysis and computation of VEP residuals from the regression function. The P2-N3 flash-VEP residuals proved EEG independent and showed relationships with dose and time after drug administration that were superimposable on those of the original data, with comparable significance levels at the drug/placebo and pre/postdrug statistical comparisons. The results indicate that VEP estimates of drug effects which are independent from EEG changes can be identified in human studies and allow some inference on the cholinergic specificity of the systems affecting late flash-VEP components. The statistical approach used in this study is suitable for application in VEP studies when effects of interacting factors are to be expected.