Topographic quantitative EEG sequelae of chronic marihuana use: a replication using medically and psychiatrically screened normal subjects.

In two previous studies it was reported that chronic marihuana (THC) use was associated with unique quantitative EEG features which were present in the non-intoxicated state. THC users, as contrasted with controls, had significant elevations of Absolute Power, Relative Power, and Coherence of alpha activity over the bilateral frontal cortex. Furthermore, a quantitative EEG discriminant function analyses permitted a 95% correct user versus non-user classification. However, because all of the THC users and 58% of the non-user controls were psychiatric inpatients, diagnostic and medication effects, if any, were uncontrolled. In the present study the same quantitative EEG methods were used to study daily THC users and non-user controls who underwent a rigorous screening process to insure that they were medically and psychiatrically healthy. The results of previous studies were replicated and an additional EEG correlate of chronic THC exposure (reduced alpha frequency) was identified.