Effect of γ-tACS on prefrontal hemodynamics in bipolar disorder: A functional near-infrared study

Objectives: Transcranial alternating current stimulation (tACS) is a potential therapeutic psychiatric tool that has been shown to modulate clinical symptoms and brain function by inducing brain oscillations. However, direct evidence on the effects of gamma-tACS ( gamma-tACS) on Bipolar I Disorder (BD -I) is limited. In the present study we used functional near -infrared spectroscopy to explore prefrontal hemodynamic changes in BD -I patients receiving combined gamma-tACS intervention in addition to pharmacological treatment. Methods: Only 39 male patients with BD -I in the acute manic phase were included, and they were randomly divided into an intervention group (n = 18) and a control group (n = 21). The intervention group received gamma-tACS treatment on a weekday for a total of 10 sessions in the right prefrontal cortex and left prefrontal cortex. All participants were pretested (baseline) and posttested (2 weeks after) with questionnaires to assess clinical symptoms and cognitive abilities, and with functional near infrared spectroscopy (fNIRS) to assess spontaneous cortical hemodynamic activities. Results: Compared to the control group, the intervention group had greater increases in Montreal Cognitive Assessment (MoCA) scores, and greater decreases in Bech-Rafaelsen Mania Rating Scale (BRMS) scores. In the intervention group, functional connectivity (FC) was significantly greater in the left hemisphere. gamma-tACS treatment resulted in a left hemispheric lateralization effect of resting state FC in BD -I patients, increasing the hemodynamic activity of the patient 's left prefrontal cortex. Conclusions: gamma-tACS can improve cognitive impairment and mood symptoms with BD -I patients in an acute manic episode by enhancing FC in the patients ' left prefrontal cortex.