Impact of Marijuana on Response Inhibition: an fMRI Study in Young Adults
Andra M. Smith, Rocío A. López Zunini, Christopher D. Anderson, Carmelinda A. Longo, Ian Cameron, Matthew J. Hogan, Peter A. Fried
Prefrontal Cortex, fMRI, Marijuana, Young Adulthood, Response Inhibition
Journal of Behavioral and Brain Science,
ABSTRACT: Rationale: Marijuana use in adolescence is prevalent and increasing. Understanding the neural correlates of the impact of this use is critical for policy making and for youth awareness. Objectives The effects of marijuana use on response inhibition were investigated in 19–21-year-olds using functional magnetic resonance imaging (fMRI). Methods: Participants were members of the Ottawa Prenatal Prospective Study, a longitudinal study that collected a unique body of information on participants from infancy to young adulthood including: prenatal drug history, detailed cognitive/behavioral performance, and current and past drug use. This information allowed for the control of an unparalleled number of potentially confounding variables including: prenatal marijuana, nicotine, alcohol, and caffeine exposure and offspring alcohol, marijuana, and nicotine use. Ten marijuana users and 14 nonusers that served as controls performed a Go/No-Go task while fMRI blood oxygen level-dependent response was examined. Results: Despite similar task performance, there was a positive relationship between amount of marijuana smoked and activation in right thalamus, premotor cortex and middle frontal gyrus. These regions form part of the neural network responsible for inhibition control. There was also a positive dose dependent relationship with marijuana and activation in inferior parietal lobe and precuneus, also parts of response inhibition pathways. Conclusions: These results suggest a dose dependent alteration in neural functioning during response inhibition after controlling for other prenatal and current drug use. These alterations may be necessary in order to compensate for neural changes in response inhibition circuits caused by long term marijuana use that began during adolescence/young adulthood.