The effects of varying doses of Δ9-tetrahydrocannabinol on the human visual and somatosensory evoked response

Abstract

The present study was designed to determine the effects of varying oral doses of Δ 9-THC on the human visual and somatosensory evoked response. Two groups of 10 subjects were studied. One group reported smoking marijuana at least twice a week (frequent user group) while subjects in the second group reported their marijuana use did not exceed twice per month (occasional user group). Δ 9-THC was extracted from raw marijuana plant material and administered orally on sugar cubes in doses of 0.2, 0.4 and 0.6 mg/kg. All subjects received each dose of Δ 9-THC and a placebo in a randomized sequence. Recording sessions were separated by at least one week. Data are reported for visual and somatosensory evoked responses recorded from frontal, central and occipital scalp 4 h after drug administration. For each response recorded under drug and placebo conditions amplitudes and latencies of consistently identifiable wave components were calculated and analyzed. No consistent evoked response differences were found between the frequent and occasional user groups. The most prominent finding was the consistency with which Δ 9-THC slowed the latency of evoked response waves while producing relatively little change in amplitude. In contrast, most drugs have been found to exert their main effects on evoked response amplitude with only slight alterations of latency. It was thus hypothesized that Δ 9-THC acts to increase the threshold of cortical and subcortical neurons or neural networks involved in producing the evoked response rather than to selectively inhibit brain-stem centers. Δ 9-THC administration produced no evidence of an excitatory action on the central nervous system. In those infrequent instances in which Δ 9-THC did produce a change in evoked response amplitude it was always a decrease. Unlike alcohol, Δ 9-THC did not alter amplitude hemispheric asymmetry.