Chronic effects of cannabis on sensory gating.

Chronic cannabis use has been associated with neurocognitive deficits, alterations in brain structure and function, and with psychosis. This study investigated the effects of chronic cannabis use on P50 sensory-gating in regular users, and explored the association between sensory gating, cannabis use history and the development of psychotic-like symptoms. Twenty controls and 21 regular cannabis users completed a P50 paired-click (S1 and S2) paradigm with an inter-pair interval of 9s. The groups were compared on P50 amplitude to S1 and S2, P50 ratio (S2/S1) and P50 difference score (S1-S2). While cannabis users overall did not differ from controls on P50 measures, prolonged duration of regular use was associated with greater impairment in sensory gating as indexed by both P50 ratio and difference scores (including after controlling for tobacco use). Long-term cannabis users were found to have worse sensory gating ratios and difference scores compared to short-term users and controls. P50 metrics did not correlate significantly with any measure of psychotic-like symptoms in cannabis users. These results suggest that prolonged exposure to cannabis results in impaired P50 sensory-gating in long-term cannabis users. While it is possible that these deficits may have pre-dated cannabis use and reflect a vulnerability to cannabis use, their association with increasing years of cannabis use suggests that this is not the case. Impaired P50 sensory-gating ratios have also been reported in patients with schizophrenia and may indicate a similar underlying pathology.