Aims: Dysfunction in inhibitory and error-evaluation systems has been highlighted in theories of the development and maintenance of addiction, but the evidence suggests the dysfunction differs by drug. Specifically, among cannabis users, the literature presents an inconsistent view of behavioural measures in support of such deficits; underlying alcohol use, which has also been linked with self-regulation problems, may explain these differences. We report a novel study examining inhibitory control in young regular cannabis users and extend on past research by controlling for alcohol use and including measurement of event-related potentials (ERPs).
Methods: 20 regular cannabis users and 74 non-users (aged 18-21 years) completed a stop-signal task while brain electrical activity was recorded. Post-experimentally, propensity weighting accounted for group differences in alcohol use. Measures include the time required to stop a response (stop-signal reaction time or SSRT), N2 and P3 amplitude and latency to stop-signals on which inhibition failed vs. was successful, and the error-related negativity and positivity (ERN and Pe, respectively) to erroneous responses.
Results: Cannabis users and non-users did not differ on SSRT, or reaction time or accuracy to Go-only trials. The groups also did not differ on ERN or Pe amplitude or latency, on N2 or P3 latency for successful or failed inhibitions, or on N2 or P3 amplitude to successful inhibitions. However, the cannabis user group displayed increased N2 amplitude, and decreased P3 amplitude, on failed inhibition trials, relative to non-users.
Discussion: Together, the results suggest intact inhibitory processing and error monitoring, but changes in conflict monitoring processes among young regular cannabis users. Limitations of the study are discussed, including the group differences in alcohol consumption, the heaviness of cannabis use, and the possibility of acute cannabis intoxication effects. Future research confirming conflict monitoring deficits among young cannabis users is indicated.