Yuko Higuchi ^1,2* Shizuka Odagiri ³ Takahiro Tateno ⁴ Michio Suzuki ^5,6 Tsutomu Takahashi ^1,2

• ¹ Department of Neuropsychiatry, University of Toyama Graduate School of Medicine and Pharmaceutical Sciences, Toyama, Japan
• ² Research Center for Idling Brain Science, University of Toyama, Toyama, Toyama, Japan
• ³ Center for Clinical Training, Toyama University Hospital, Toyama, Japan
• ⁴ Uozu Shinkei Sanatorium, Uozu, Japan
• ⁵ Itoigawa Clinic, Itoigawa, Japan
• ⁶ Arisawabashi Hospital, Toyama, Toyama, Japan

Background and Objectives: Several studies have reported on the resting-state electroencephalogram (EEG) power in patients with schizophrenia, with a decrease in α (especially α2) and an increase in δ and β1 power compared with healthy control; however, reports on at-risk mental states (ARMS) are few. In this study, we measured the resting-state EEG power in ARMS, and investigated its features and the relationship between the power of the frequency bands and their diagnostic outcomes.Methods: Patients with ARMS who were not on any psychotropic medication and met the Comprehensive Assessment of At-Risk Mental State criteria were included. Patients who developed psychotic disorders were labeled as the ARMS-P group, while patients with ARMS who were followed up prospectively for more than 2 years and did not develop psychotic disorders were classified as the ARMS-NP group. EEGs were measured in the resting state, and frequencies were analyzed using standardized low-resolution brain electromagnetic tomography (sLORETA). Seven bands (δ, θ, α1, α2, β1-3) underwent analysis. The sLORETA values (current source density [CSD]) were compared between the ARMS-P and ARMS-NP groups. Clinical symptoms were assessed at the time of EEG measurements using the Positive and Negative Syndrome Scale (PANSS).Results: Of the 39 patients included (25 males, 14 females, 18.8±4.5 years old), eight developed psychotic disorders (ARMS-P). The ARMS-P group exhibited significantly higher CSD in the β1 power within areas of the left middle frontal gyrus (MFG) compared with the ARMS-NP group (best match: X=-35, Y=25, Z=50 [MNI coordinates], Area 8, CSD=2.33, p<0.05). There was a significant positive correlation between the β1/α ratio of the CSD at left MFG and the Somatic concern score measured by the PANSS. Discussion: Increased β1 power was observed in the resting EEG before the onset of psychosis and correlated with a symptom. This suggests that resting EEG power may be a useful marker for predicting future conversion to psychosis and clinical symptoms in patients with ARMS.