Mismatch negativity in tobacco-naïve cannabis users and its alteration with acute nicotine administration.

Chronic cannabis use may interact with factors, such as age of onset of cannabis use, family history, and genetic factors, to elicit schizophrenia (SZ)-like symptoms, including sensory and cognitive deficits. However, evidence of a relationship between cannabis use and cognitive impairment is confounded by concomitant use of tobacco. The objective of this study was to compare tobacco-naïve cannabis users with individuals without a history of tobacco/cannabis use on the auditory mismatch negativity (MMN) event-related potential (ERP), a neural measure of auditory deviance detection which is diminished in SZ. An exploratory arm of the study, conducted within a randomized, double-blind, placebo controlled design, examined the acute effects of nicotine gum (6mg) on MMN in cannabis users. MMN was recorded in response to 5 deviant stimuli within an optimal MMN paradigm in 44 healthy, non-tobacco smoking volunteers aged 18-26. Cannabis users (n=21) started smoking cannabis prior to age 17, at least 1 joint per month. To examine the effects of chronicity, users were grouped into relatively heavy long-term (HLT; n=11) users and light short-term (LST; n=10) users. Impaired deviance detection was shown in cannabis users vs. nonusers as reflected by a smaller MMN to duration deviants. Chronicity of use was also associated with MMN alterations, as HLTs displayed a reduced duration and gap MMN vs. LSTs. Compared with placebo, nicotine treatment enhanced select MMN deviants in cannabis user subgroups. As deficits associated with early and persistent cannabis use are similar to those seen in SZ, these dose-dependant disturbances in early sensory processing with cannabis use may be one cognitive pathway which mediates an increased risk for SZ in vulnerable youth, and be influenced by concurrent cigarette smoking behavior.