The impact of initiation: Early onset marijuana smokers demonstrate altered Stroop performance and brain activation

Abstract

Marijuana (MJ) use is on the rise, particularly among teens and emerging adults. This poses serious public health concern, given the potential deleterious effects of MJ on the developing brain. We examined 50 chronic MJ smokers divided into early onset (regular MJ use prior to age 16; n=24) and late onset (age 16 or later; n=26), and 34 healthy control participants (HCs). All completed a modified Stroop Color Word Test during fMRI. Results demonstrated that MJ smokers exhibited significantly poorer performance on the Interference subtest of the Stroop, as well as altered patterns of activation in the cingulate cortex relative to HCs. Further, early onset MJ smokers exhibited significantly poorer performance relative to both HCs and late onset smokers. Additionally, earlier age of MJ onset as well as increased frequency and magnitude (grams/week) of MJ use were predictive of poorer Stroop performance. fMRI results revealed that while late onset smokers demonstrated a more similar pattern of activation to the control group, a different pattern was evident in the early onset group. These findings underscore the importance of assessing age of onset and patterns of MJ use and support the need for widespread education and intervention efforts among youth.

Keywords: Age of onset; Cognition; Executive function; Marijuana; Stroop; fMRI.

Fig. 1

Logarithmic regression analysis: age of onset of MJ use vs Stroop Interference commission errors. Within the MJ smokers, earlier age of onset was significantly associated with poorer performance on the Stroop Interference subtest, including increased commission errors, or incorrect responses (R² = .076, F(1, 48) = 3.929, p = .027).

Fig. 2

Stroop (interference-rest/fixation)–(color naming-rest/fixation) fMRI activation: single-group comparison. Single-group comparisons on the Stroop Interference condition: HCs (A) demonstrated robust posterior activation in the right cingulate, while MJ smokers (B) exhibited more diffuse activation throughout the cingulate. Within MJ smokers, the early onset group (C) demonstrated activation in the anterior region of the cingulate, adjacent to the genu of the corpus callosum, whereas late onset smokers (D) exhibited posterior activation in the right cingulate, more similar to the HC group.