Local chemoarchitecture explains widespread lower cortical thickness associated with clinical high risk for psychosis.

The Clinical High Risk (CHR) state for psychosis is consistently associated with widespread cortical thinning. However, the underlying mechanisms driving this neuroanatomical phenotype remain poorly understood. Here, we integrated the ENIGMA CHR Working Group's large pooled dataset (N = 1782 CHR, N = 1333 healthy controls) with an open-source PET molecular atlas to identify, for the first time, potential neurochemical drivers of cortical thinning associated with psychosis risk, transition, and its core symptoms. Using multilinear model analysis, we show that local chemoarchitecture significantly explains CT differences associated with CHR case-control status, the severity of negative symptoms, and future psychosis transition after excluding medication confounds. PET-based maps of dopamine, GABA, glutamate, serotonin, and norepinephrine consistently emerged as the strongest predictors of lower CT in CHR and psychosis transition (total dominance range: 62-69% and 58-87%, respectively), with contributions of monoamine systems being especially sensitive to medication exposure (8-23% change in dominance range). Negative symptom-associated cortical thinning was best explained by PET-based maps of dopamine, histamine, serotonin and opioid systems (total dominance range: 60-81%), with contributions of histamine being sensitive to medication exposure (9-19% change in dominance range). Combined, these results uniquely identify specific neurochemical systems - particularly monoaminergic, glutamatergic, and GABAergic pathways - as key molecular mechanisms associated with cortical thinning in people at high risk of developing psychosis.