Topographic mapping of quantitative EEG variables in chronic heavy marihuana users: empirical findings with psychiatric patients.

EEG studies of marihuana use dating back to 1945 were reviewed. The earlier studies depended upon visual analysis of the tracing, and while some minor frequency and amplitude variations occurred in some subjects, there was no consistent THC induced change noticeable across subjects. Quantitative EEG studies of acute exposure to THC came later and produced reliable findings of a placebo controlled dose dependent THC induced increase in relative power of alpha, combined with decreased alpha frequency and a reduction of beta activity. These findings were reported for data collected from central-occipital derivations only. In our present investigation, we report that chronic heavy THC users have EEGs characterized by (1) increased absolute power of all frequencies over all cortical areas (2) hyperfrontality of elevated relative and absolute power and coherence values of alpha activity, and (3) a decrease in relative power of all non-alpha frequencies. Methodological issues were discussed and some suggestions were made for continuing research in this area.