A systematic review of 91 fMRI studies on acute psychedelic effects found substantial methodological heterogeneity. Only 51 unique samples were used across the 91 papers, and 54% of studies did not meet current standards for correcting Type I errors or controlling motion artifacts. Psilocybin and LSD consistently modulated connectivity along the sensorimotor-association cortical axis. Ketamine consistently increased activation in the dorsomedial prefrontal cortex. The review calls for future adoption of pre-registration, standardized processing and statistical testing, and data sharing to improve rigor.
Cannabis use is linked to higher psychosis risk, and this study examined whether brain glutamate levels in the anterior cingulate cortex (ACC) relate to symptoms depending on cannabis use. Among 79 participants across the psychosis spectrum, higher ACC glutamate independently predicted greater positive and negative symptoms. However, in cannabis users, lower glutamate was associated with more positive symptoms. Psychosis patients who used cannabis had lower ACC glutamate, suggesting glutamatergic dysfunction may amplify symptom severity. The findings implicate ACC glutamate as a transdiagnostic correlate of symptom burden, especially in cannabis users with psychosis.