Functional Outcome in People at High Risk for Psychosis Predicted by Thalamic Glutamate Levels and Prefronto-Striatal Activation

Little is known about the neurobiological factors that determine functional outcome in people at high risk for psychosis. We use multimodal neuroimaging to investigate whether cortical responses during a cognitive task and thalamic glutamate levels were associated with subsequent functional outcome. Sixty subjects participated: 27 healthy controls (CTRL) and 33 at ultrahigh risk (UHR) for psychosis. At baseline, cortical responses during a verbal fluency task were measured using functional Magnetic Resonance Imaging (fMRI) and proton Magnetic Resonance Spectroscopy (1H-MRS) was used to measure thalamic glutamate levels. The UHR subjects were then followed clinically for a mean duration of 18 months, and subdivided into “good” and “poor” functional outcome subgroups according to their Global Assessment of Function score at follow-up. UHR subjects with a poor functional outcome showed greater cortical and subcortical activation than UHR subjects with a good functional outcome. They also had lower levels of thalamic glutamate and showed a negative relationship between thalamic glutamate levels and prefrontal-striatal activation that was not present in the good functional outcome or control groups. In people at high risk for psychosis, their subsequent level of functioning may depend on the extent to which neurophysiological and neurochemical function is perturbed when they first present to clinical services.Key words: psychosis, ultra-high risk, functional outcomes, functional MRI, spectroscopy, glutamate