Psychosis and Cannabis: An Investigation of Individual and Combined Effects on Cognition and White Matter

Abstract

Reduced cognitive functioning has been observed in individuals with early phase psychosis (EPP) and is similar to reductions in cognitive functioning in nonpsychiatric populations who use cannabis. Less clear, however, is the combined effect of EPP and cannabis use on cognition. Furthermore, it is believed that reduced white matter integrity occurs in the brains of individuals with EPP and cannabis users and may underlie the noted dysfunctions. To clarify the impact of cannabis use and EPP individually, as well as the combined effect, two studies were executed. Study 1 utilized a clinical database of EPP patients with low/no or moderate/severe cannabis use and found those with moderate/severe use had better psychomotor speed and working memory. Prospective data was collected for Study 2 which included a healthy control comparison group as well as structural white matter neuroimaging techniques to investigate the individual and combined effects of EPP and cannabis use on cognition and white matter integrity. Controls outperformed EPP patients on tasks of working memory, executive functioning, and psychomotor speed. Cannabis use negatively impacted working memory, executive functioning, and verbal learning and memory. The integrity of white matter in the left prefrontal region was reduced for those with EPP compared to controls. Cannabis use did not affect white matter. High rates of cannabis use in those with EPP warrant further investigation into the relationship between EPP and cannabis use to assess the individual and combined impacts of each on cognitive functioning and white matter.