In a double-blind study, the amplitude of the contingent negative variation (CNV) was assessed in 12 normal men given placebo and quantified "social" doses of 1-δ9-transtetrahydrocannabinol (THC) and alcohol (ethyl alcohol). Using subjects as their own controls, it was found that THC selectively enhanced the amplitude as compared to placebo while alcohol depressed it.
Kopell BS, Tinklenberg JR, Hollister LE. Contingent Negative Variation AmplitudesMarihuana and Alcohol. Arch Gen Psychiatry. 1972;27(6):809-811. doi:10.1001/archpsyc.1972.01750300071012