Abstract
Many prominent theories of visual anomalies (e.g., hallucinations) in schizophrenia suggest differences in neurotransmitter levels in the visual cortex. For example, imbalances in excitatory and inhibitory neurotransmitters (e.g., glutamate and GABA) may contribute to psychotic symptoms. Previous studies using proton magnetic resonance spectroscopy (MRS) have reported differences in concentrations of GABA, glutamate, glutamine, N-acetyl aspartate (NAA), and glutathione (GSH) among patients with schizophrenia. It is not yet clear whether neurochemical differences are specific to schizophrenia, or may be present among patients with psychotic disorders more broadly. The role of genetic risk for psychosis in neurochemical dysfunction is also not clear. We sought to determine whether and how patterns of neurochemical concentrations in the visual cortex might differ in people with psychosis and their first-degree biological relatives. As part of the ongoing Psychosis Human Connectome Project, we acquired 7 T MRS (STEAM) data in the visual cortex, scaled to water, from 45 patients with a psychotic disorder (schizophrenia, schizoaffective disorder, or bipolar disorder), 29 non-psychotic biological relatives, and 36 healthy controls. We found no significant univariate differences in GABA or glutamate levels between groups. There were trends towards group differences for several other metabolites, including NAA and macromolecules, but these did not survive correction for multiple comparisons. Using 5-fold cross-validated multivariate decoding (support vector machine) analyses, we sought to differentiate between patients, relatives, and controls based on the pattern of metabolite concentrations in the visual cortex from MRS. Preliminary results from our decoding analysis suggest that the neurochemical profile from MRS may reflect neural dysfunction in early visual cortex among patients with psychosis, and may be associated with genetic risk for psychosis.