[Identifying common neural circuit dysfunctions across psychiatric disorders through neurophysiological indices].

The etiology of psychiatric disorders such as schizophrenia, autism spectrum disorder (ASD), and depression remains largely unknown, and to date, no clear diagnostic criteria or curative pharmacological treatments have been established. One contributing factor is that patients with psychiatric disorders actually represent a heterogeneous population, yet are treated as a single group in clinical trials, which lowers the success rate of drug development. Against this background, there has been growing advocacy for stratification based on objective biomarkers, such as those proposed in the Research Domain Criteria (RDoC), rather than relying solely on syndrome-based classifications such as the DSM-5 or ICD-11 for diagnosis and therapeutic development. Furthermore, the elucidation of psychiatric pathophysiology and the development of effective pharmacological and therapeutic interventions require common objective indices that can bridge human and animal studies to enable translational research between preclinical and clinical domains. In patients with schizophrenia, sleep disturbances are consistently observed with high reproducibility, and abnormalities in sleep spindle generation during non-REM sleep have recently attracted attention as a novel biomarker. Moreover, spindle abnormalities have also been reported not only in schizophrenia but in subsets of patients with Alzheimer's disease, ASD, and Parkinson's disease, suggesting the possibility of shared pathophysiological mechanisms across distinct psychiatric and neurological disorders. In this article, I highlight electroencephalographic markers such as non-REM sleep spindles and gamma oscillations-objective neurophysiological indices measurable in both humans and experimental animals-that may deepen our understanding of the pathophysiology of psychiatric disorders and ultimately contribute to the development of novel therapeutics.