Glutamate, Contextual Insensitivity, and Disorganized Speech in First-Episode Schizophrenia: A 7T Magnetic Resonance Spectroscopy Study

Background

In people with schizophrenia, formal thought disorder is a core symptom that emerges early and persists into chronic stages despite treatments. It manifests as disorganized speech and is often associated with poor long-term outcomes. A key feature of this disorganization is an impairment in the buildup and use of context provided by preceding words when choosing upcoming words. Recent work has shown that spoken words are less predictable based on global linguistic context in schizophrenia, but the neural basis of this remains unknown. Glutamate dysfunction in the anterior cingulate cortex has long been implicated in schizophrenia, but its connection to behavioral impairments remains unclear.

Methods

In this study, we investigated the relationship between linguistic contextual sensitivity and glutamate level in the dorsal anterior cingulate cortex in 39 patients with first-episode psychosis (33 men) and 33 sociodemographically matched healthy control participants (22 men). Contextual sensitivity was measured using a large language model (GPT-3), and glutamate levels were measured using 7T magnetic resonance spectroscopy.

Results

We found a significant interaction between diagnosis and glutamate level in predicting contextual sensitivity: Patients with lower glutamate levels had poor contextual sensitivity, a relationship not seen in healthy control participants. Glutamate variation was specifically explained by contextual sensitivity after controlling for other clinical and language variables, underscoring the robustness and specificity of this association.

Conclusions

These results highlight a potential glutamatergic basis for disorganized speech in schizophrenia and suggest that contextual sensitivity in speech could reflect anterior cingulate glutamate variations in early psychosis.