Relationship between fMRI response during a nonverbal memory task and marijuana use in college students

Abstract

Marijuana (MJ) is widely used among college students, with peak use between ages 18-22. Research suggests memory dysfunction in adolescent and young adult MJ users, but the neural correlates are unclear. We examined functional magnetic resonance imaging (fMRI) response during a memory task among college students with varying degrees of MJ involvement. Participants were 64 college students, ages 18-20, who performed a visual encoding and recognition task during fMRI. MJ use was ascertained for 3 months prior to scanning; 27 individuals reported past 3-month MJ use, and 33 individuals did not. fMRI response was modeled during encoding based on whether targets were subsequently recognized (correct encoding), and during recognition based on target identification (hits). fMRI response in left and right inferior frontal gyrus (IFG) and hippocampal regions of interest was examined between MJ users and controls. There were no group differences between MJ users and controls on fMRI response during encoding, although single sample t-tests revealed that MJ users failed to activate the hippocampus. During recognition, MJ users showed less fMRI response than controls in right hippocampus (Cohen's d = 0.55), left hippocampus (Cohen's d = 0.67) and left IFG (Cohen's d = 0.61). Heavier MJ involvement was associated with lower fMRI response in left hippocampus and left IFG. This study provides evidence of MJ-related prefrontal and hippocampal dysfunction during recognition memory in college students. These findings may contribute to our previously identified decrements in academic performance in college MJ users and could have substantial implications for academic and occupational functioning.

Keywords: Adolescence; Marijuana; Memory; fMRI.

Figure 1.

Average BOLD response in each ROI during encoding of stimuli that were subsequently correctly recognized. Error bars represent +/− 1 standard error. * Single sample t-test shows significant BOLD response (p < .05)

Figure 2.

Average BOLD response in each ROI during recognition “hits.” Error bars represent +/− 1 standard error. * Single sample t-test shows significant BOLD response (p < .05) ** Between groups t-test shows significant difference in BOLD response (p < .05)

Figure 3.

Whole-brain group differences in BOLD response during correct encoding (voxel-wise p<.05, uncorrected, cluster size 2700μl for display purposes). Blue regions indicate areas where MJ users showed less BOLD response than controls.

Figure 4.

Whole-brain group differences in BOLD response during recognition hits (voxel-wise p<.05, uncorrected, cluster size 2700μl for display purposes). Blue regions indicate areas where MJ users showed less BOLD response than controls.