High-Intensity tACS Improves Chronic Insomnia by Modulating Brain Networks

A randomized trial shows 15 mA stimulation reduces sleep index scores and reorganizes functional connectivity in hyperarousal circuits.

For Doctors in a Hurry

Clinicians lack effective non-pharmacological interventions for chronic insomnia, prompting investigation into high-intensity transcranial alternating current stimulation.
The researchers conducted a double-blind, randomized, sham-controlled trial involving 18 patients over a four-week treatment period.
Active stimulation reduced Pittsburgh Sleep Quality Index scores from 13.8 to 7.7, a statistically significant improvement (p < 0.001).
The authors conclude that stimulation reorganizes brain network topology by increasing global efficiency within the Default and Salience networks.
These findings suggest that high-intensity stimulation may serve as a viable clinical intervention for patients suffering from chronic insomnia.

Targeting Neural Hyperarousal in Chronic Insomnia

Chronic insomnia remains a pervasive clinical challenge, frequently persisting despite first-line interventions such as cognitive behavioral therapy or short-term pharmacotherapy [1]. Current clinical guidelines emphasize the need for evidence-based alternatives for patients who do not achieve remission, as persistent sleep disturbances are linked to significant systemic comorbidities [2, 1]. Neuroimaging research suggests that the pathophysiology of insomnia involves aberrant functional connectivity within the salience network and the default mode network, which are associated with clinical hyperarousal and cognitive rumination [3]. Non-invasive neuromodulation, particularly transcranial alternating current stimulation, has emerged as a potential strategy to target these specific neural circuits by modulating cortical oscillations [4, 5]. Recent trials have indicated that this modality can improve sleep efficiency and total sleep time, though the underlying mechanisms of network reorganization remain a subject of active investigation [2]. A new study now offers fresh insights into the specific topological changes and network-level effects associated with high-intensity stimulation.

Clinical Response to High-Intensity Stimulation

The researchers conducted a 4-week, double-blind, randomized, sham-controlled trial to evaluate the efficacy of high-intensity transcranial alternating current stimulation (tACS) for patients with chronic insomnia. The intervention utilized a specific stimulation intensity of 15 mA, a level chosen to modulate the neural circuits associated with sleep-wake regulation. A total of eighteen patients completed the full study protocol, which included the longitudinal resting-state MRI scans necessary to correlate clinical improvements with changes in brain architecture. The primary clinical outcome was measured using the Pittsburgh Sleep Quality Index (PSQI), a self-report questionnaire that assesses sleep quality and disturbances over a one-month period, where higher scores indicate poorer sleep. In the active tACS group, PSQI scores decreased from 13.8 (3.0) at baseline to 7.7 (3.0) following the intervention, representing a statistically significant improvement (p < 0.001). This reduction suggests that the high-intensity stimulation moved patients from a state of severe sleep disruption toward a much more manageable clinical profile. In contrast, the sham group, which received a placebo stimulation to account for the Hawthorne effect or patient expectations, showed no meaningful clinical recovery. The PSQI scores in the sham group changed from 13.8 (2.9) to 13.9 (2.4), a result that lacked statistical significance (p = 0.74). These data points underscore that the observed improvements in the active group were likely due to the physiological effects of the 15 mA current rather than a placebo response, providing a clear distinction between the two cohorts in terms of therapeutic benefit.

Downregulation of Spontaneous Activity and Connectivity

The therapeutic effects of the 15 mA transcranial alternating current stimulation were associated with significant physiological changes in resting-state neural function. Following the four-week intervention, the researchers observed extensive reductions in spontaneous brain activity within the Default Network, a system of interconnected regions typically associated with self-referential thought and internal reflection. Similar reductions in spontaneous brain activity were identified in the Salience/Ventral Attention Network, which plays a critical role in detecting and filtering relevant sensory stimuli. These physiological shifts were closely tied to patient outcomes, as the reductions in spontaneous brain activity showed a negative correlation with the increase in clinical sleep scores. This correlation suggests that the dampening of baseline activity in these specific networks is a primary driver of the observed improvements in sleep quality. The study further examined how the intervention reorganized the communication between distant brain regions by measuring functional connectivity (the temporal correlation between spatially remote neurophysiological events). The analysis revealed that functional connectivity was significantly altered within the Default Network and the Salience/Ventral Attention Network following the treatment protocol. Crucially, the majority of functional connectivity changes in these networks displayed a decreasing trend, indicating a reduction in the pathological over-synchronization often seen in the hyperarousal state of chronic insomnia. By attenuating these internal communication pathways, the high-intensity stimulation appears to reset the neural circuits that otherwise prevent patients from transitioning into and maintaining restful sleep.

Topological Reorganization of Sleep Circuits

To understand how high-intensity stimulation alters the underlying architecture of the brain, the researchers employed graph theoretical analysis (a mathematical framework used to model the brain as a complex network of nodes and connections). This analysis revealed a significant topological reorganization within the Default and Salience/Ventral Attention networks of the 18 patients who completed the trial. This structural shift suggests that the clinical efficacy of 15 mA transcranial alternating current stimulation stems from its ability to reshape the fundamental organization of neural circuits involved in hyperarousal, rather than simply modulating isolated brain regions. The observed network reorganization was characterized by reduced clustering coefficients (a measure of the degree to which nodes in a graph tend to cluster together). In patients with chronic insomnia, high clustering often reflects a pathological over-segregation of neural processing that maintains a state of constant alertness. Furthermore, the intervention led to reduced characteristic path lengths, representing the average number of steps required to connect any two nodes in the network. By shortening these paths, the stimulation appears to facilitate more direct communication across the brain, potentially allowing for more flexible transitions between the cognitive states required for wakefulness and the physiological states required for sleep. These changes in network architecture were coupled with increased global efficiency (a metric representing the capacity of a network for parallel information transfer). This increase in efficiency indicates that the treatment optimized the brain's communication pathways, moving the neural environment toward a more integrated and less effortful state of processing. When viewed alongside the significant reduction in Pittsburgh Sleep Quality Index scores from 13.8 (3.0) to 7.7 (3.0) with a p-value of less than 0.001, these findings provide a clear mechanical link between the topological reorganization of the brain and the resolution of chronic insomnia symptoms. For the practicing clinician, these data suggest that high-intensity stimulation acts as a corrective tool for the rigid and inefficient network configurations that characterize the hyperaroused brain.

Study Info

Modulating Default and Salience/Ventral Attention networks: Exploring the treatment effect of transcranial alternating current stimulation on chronic insomnia

Hongxing Wang, Danhao Zheng, Jing Huang, Wenfeng Zhao, et al.

Journal Psychotherapy and Psychosomatics

Published April 20, 2026