Synergistic effects of marijuana abuse and HIV infection on neural activation during a cognitive interference task

Abstract

Marijuana use, which is disproportionately prevalent among human immunodeficiency virus (HIV)-infected persons, can alter activity in fronto-parietal regions during cognitively demanding tasks. While HIV is also associated with altered neural activation, it is not known how marijuana may further affect brain function in this population. Our study examined the independent and additive effects of HIV infection and regular marijuana use on neural activation during a cognitive interference task. The sample included 93 adults who differed on marijuana (MJ) and HIV statuses (20 MJ+/HIV+, 19 MJ+/HIV-, 29 MJ-/HIV+, 25 MJ-/HIV-). Participants completed a counting Stroop task during a functional magnetic resonance imaging scan. Main and interactive effects on neural activation during interference versus neutral blocks were examined using a mixed-effects analysis. The sample showed the expected Stroop effect for both speed and accuracy. There were main effects of MJ in the right and left inferior parietal lobules, with the left cluster extending into the posterior middle temporal gyrus and a main effect of HIV in the dorsal anterior cingulate cortex. There was an interaction in the left fronto-insular cortex, such that the MJ+/HIV+ group had the largest increase in activation compared with other groups. Among MJ+, signal change in this cluster correlated positively with cumulative years of regular marijuana use. These results suggest that comorbid HIV and marijuana use is associated with complex neural alterations in multiple brain regions during cognitive interference. Follow-up research is needed to determine how marijuana-related characteristics may moderate HIV neurologic disease and impact real-world functioning.

Keywords: HIV; Stroop; cannabis; functional magnetic resonance imaging (fMRI); inhibitory control; marijuana.

Figure 1.. Mean activation and deactivation maps for the counting Stroop task.

Overall task activation across all participants for: (A) interference > neutral stimuli, and (B) interference < neutral stimuli. Cluster information is described in Supplementary Table 1. Activation maps were thresholded using clusters determined by Z >3.5 and a corrected cluster significance threshold of p= 0.05. The underlying image is the MNI152 2mm standard-space T1-weighted structural template. Images are in radiological orientation (left = right, right = left).

Figure 2.. Effects of marijuana use and HIV infection on neural activation during the counting Stroop task.

On the left, images show the clusters that exhibited significant F-values in the 2 (MJ status) by 2 (HIV status) between-subjects general linear model for the interference > neutral contrast. The Z-statistic images were thresholded at 2.3 with a cluster p threshold of 0.05. The underlying image is the MNI152 2mm standard-space T1-weighted structural template, and images are in radiological orientation (left = right, right = left). The four significant clusters are characterized further in Table 3. On the right, bar graphs show the percent BOLD signal change by group (error bars represent standard error from the mean).

Figure 3.. Association between neural activation during the counting Stroop task and years of regular marijuana use.

BOLD signal change was extracted from the fronto-insular cluster where the ANOVA identified an HIV*Marijuana interaction effect. The standardized residuals from the partial correlations controlling for age, education, protocol, and DVAR are plotted. These analyses were restricted to MJ+ participants, and HIV+ and HIV− groups are shown separately. The r-values represent the partial correlation coefficients. *p<.05, **p<.01.