Effects of caffeine on resting EEG and response to sine wave modulated light.

A double blind, placebo controlled study was designed to assess transient caffeine effects on spontaneous and evoked brain activity in man. Twelve normal males received 200 mg caffeine citrate or placebo on separate occasions. EEG from left and right occipital regions was recorded in the absence of stimulation and during the response to sine wave modulated light (SML). The photic stimulation frequencies were 5, 10, 15, 18 and 24 c/sec. EEG power at frequencies corresponding to fundamental and selected harmonics of stimulation frequencies was obtained. The time course of response to SML was studied over a period of 2 min. Caffeine reduced the EEG power under resting conditions and during SML stimulation. This reduction was statistically significant at 10 and 15 c/sec. At 24 c/sec, caffeine reduced the fundamental SML response, but not the resting EEG power. Evaluation of the SML response time course did not reveal any consistent tendencies. It appears that the response is sustained in a stable way over the period of 2 min.