'Pink Noise' Stimulation Approach Could Support Safer Anesthesia

Sudden nociceptive surges can disrupt anesthetic depth, increasing neurological stress and the risk of hemodynamic instability. These disruptions are linked to alterations in delta-wave brain activity that mark anesthetic unconsciousness. To help address this challenge, researchers have developed a closed-loop auditory stimulation approach that uses carefully timed bursts of pink noise during surgery to strengthen slow brain waves.

Researchers at Université de Montréal, working through the Centre for Advanced Research in Sleep Medicine and the Integrated Trauma Centre at Montreal’s Sacré-Cœur Hospital, are evaluating closed-loop auditory stimulation (CLAS) for patients undergoing elective surgery. The method targets the brain’s delta oscillations that characterize unconscious states under anesthesia. The work is described in a study protocol published in Frontiers in Human Neuroscience in 2026.

CLAS operates by coupling real-time electroencephalography (EEG) monitoring with automated delivery of brief, 50‑millisecond pink-noise bursts through specialized earbuds. The system detects ongoing delta waves and times the stimulus to specific phases of the oscillation. Sleep research has shown that stimulation stimulation at wave peaks can strengthen slow waves, whereas stimulation at the troughs can disturb them. The intraoperative protocol adapts this timing logic to the anesthetized brain.

Early tests in a small number of surgical patients suggest that delivering stimulation just before the troughs may most effectively amplify delta activity under anesthesia. This preliminary observation differs from sleep findings, indicating that optimal phase targeting during anesthesia may not mirror nocturnal physiology. The team is continuing investigations to confirm the effect, clarify mechanisms, and define clinical parameters for use in the operating room.

The researchers note that maintaining robust delta waves could help stabilize anesthetic depth despite nociceptive inputs generated by surgical trauma. If proven effective, the approach could lower anesthetic drug requirements, a potential advantage for physiologically fragile patients prone to complications. Additional applications mentioned include intensive care unit sedation and stabilization strategies for patients with brain injuries, where current regimens can cause side effects that impede recovery.

“We use pink noise, which sounds a bit like a waterfall but lasts only 50 milliseconds. Unlike white noise, which has equal volume across all pitches, pink noise is more intense in the lower frequencies while still spanning the entire sound spectrum,” said Catherine Duclos, professor in the Department of Anesthesiology and Pain Medicine and the Department of Neuroscience at Université de Montréal, and researcher at the Centre for Advanced Research in Sleep Medicine and the Integrated Trauma Centre at Montreal’s Sacré-Cœur Hospital.

Related Links
Université de Montréal
Centre for Advanced Research in Sleep Medicine