Date of Award

August 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Psychology

First Advisor

Krista M Lisdahl

Committee Members

Cecelia Hillard, Bonita Klein-Tasman, Chris Larson, Hanjoo Lee

Keywords

Alcohol, DTI, Emerging adulthood, Marijuana, White Matter

Abstract

Objective: Growing evidence suggests alcohol and cannabis use independently alter neural structure and functioning, particularly during sensitive developmental time periods such as adolescence and emerging adulthood. However, there has been minimal investigation into the effects co-occurring use of these two substances, despite preliminary evidence of unique acute and psychopharmacological changes due to using alcohol and cannabis together.

Method: Data drawn from the IDEAA Consortium was utilized to assess white matter integrity as measured by FreeSurfer’s TRACULA in emerging adults (n=192; 16-27 years old). Timeline Follow-Back was used to calculate past month cannabis use, alcohol use, co-use days, binge alcohol episode, and co-use-binge days. The Stroop task was administered and normed scores were used. Multiple regressions investigated white matter integrity by past month cannabis, alcohol, and co-use days, controlling for appropriate covariates (e.g., site, gender, education, length of abstinence). Analyses were run twice, once with alcohol as measured in standard units and once with binge episodes. Follow-up brain-behavior analyses assessed whether substance use or tracts that differed significantly by substance use then related to Stroop performance. Correction for multiple comparisons was conducted using Benjamini and Hochberg’s (1995) False Discovery Rate correction method.

Results: Corrected for multiple comparisons, cannabis use was significantly related to increased mean diffusivity in 12 fronto-limbic and fronto-parietal tracts. Cannabis use also associated with poorer performance on Stroop word reading. Within the MJ+ALC group, increased mean diffusivity associated with better Stroop interference performance.

Discussion: The present study found cannabis use was associated with decreased white matter integrity, as measured by mean diffusivity, across fronto-parietal and fronto-limbic tracts. These results suggest a robust relationship between cannabis use and white matter integrity in this neurodevelopmentally sensitive time period. Despite our hypotheses, co-use, alcohol use, and binge drinking did not significantly predict any measures. Future research should further investigate the potential independent and interactive affects of these substances on preclinical and clinical levels. Efforts should be made to inform the public of the likely negative impact of cannabis on white matter quality.

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