Attention-deficit/hyperactivity disorder (ADHD) and impulsivity have been linked to the functioning of the brain’s reward network. However, many of these studies focus on the anticipatory phase of reward processing and are limited by small sample sizes. In the current study, a community sample of 1081 adults (mean age = 28.8, SD = 3.7) completed a computerized functional magnetic resonance imaging task examining reward outcome. Out-of-scanner participants completed self-report measures of ADHD symptoms and impulsivity. A voxelwise t-test of activation during reward outcomes indicated activation in the left and right ventral striatum, the ventromedial prefrontal cortex, and the posterior cingulate, as well as greater activation in sensory and motor areas. In voxelwise regression analyses, neural response to reward in the left striatum, insula, dorsolateral prefrontal cortex, and lateral temporal cortex, as well as bilaterally in the occipital cortex, was inversely associated with inattentive symptoms of ADHD. No associations were found between neural response to reward and hyperactive symptoms of ADHD or impulsivity. Results were generally consistent in follow-up region of interest analyses. These findings suggest activation in reward network regions is linked to inattentive, but not hyperactive symptoms of ADHD, even in those without a diagnosis.

There is mixed evidence that individuals who use cannabis have reduced hippocampal and amygdalar gray matter volume, potentially because of small sample sizes and imprecise morphological characterization. New automated segmentation procedures have improved the measurement of these structures and allow better examination of their subfields, which have been linked to distinct aspects of memory and emotion. The current study applies this new segmentation procedure to the Human Connectome Project Young Adult dataset (N = 1081) to investigate associations of cannabis use with gray matter volume in the hippocampus and amygdala. Results revealed significant bilateral inverse associations of hippocampal volume with recent cannabis use (positive THC urine drug screen) and total lifetime consumption (ps<.001), as well as association of the left amygdala total lifetime consumption (p<.001). Hippocampal subfield analyses indicated these associations were primarily driven by the head of the hippocampus, the first section of the cornu amonis (CA1), and the subicular complex, which have been linked to verbal working memory, episodic memory, and spatial memory respectively. In the amygdala, the association was driven by subfields in the basolateral complex, which links the amygdala to the cortex and is critical in emotion regulation. No associations were detected for age of cannabis initiation or lifetime presence of cannabis use disorder. In one of the largest studies to date, these results support the hypothesis that cannabis use is linked with hippocampal and amygdalar volume and clarify both the specific subfields and the specific aspects of cannabis use that are responsible for these links.