Ultrasound pulses helped map responses in a deep brain region involved in pain and mood

Ultrasound pulses helped map responses in a deep brain region involved in pain and mood

On August 19, the authors posted a scientific preprint analyzing 36 participants: 19 with chronic pain and 17 with depression that had responded poorly to standard treatment. After brief ultrasound stimulation at neighboring sites in the anterior cingulate cortex, participants reported positive changes more often than after a sham procedure.

The anterior cingulate cortex is a deep region along the brain's midline that contributes to pain experience and mood regulation. The authors tested whether they could stimulate several nearby sites in this region in sequence, collect a brief self-report after each stimulation, and identify sites that produced consistent responses.

An MRI scan linked the stimulation coordinates to each participant's anatomy. A dual array of ultrasound transducers accounted for distortion of the beam by the skull and moved the focus between sites approximately four millimeters apart. After each trial, which lasted from 30 seconds to three minutes, the participant reported whether their pain or mood had changed. This allowed the researchers to associate each site with the participant's immediate response.

In two preliminary studies, each participant underwent both the active and sham procedures at separate visits. In both conditions, participants heard white noise and a recording of the pulses through headphones. During the sham procedure, the device delivered no ultrasound energy. The researchers classified 29% of 807 responses after active stimulation and 8% of 797 responses after the sham procedure as positive.

The response maps differed between the groups. In participants with chronic pain, the largest difference from the sham procedure was found in the anterior part of the anterior cingulate cortex. In participants with depression, it was found in the middle section of the region's lower part. Participants with a higher proportion of positive responses at the first visit showed greater reductions in pain or depressive symptom severity 24 hours later.

For these protocols, the authors established a sequence that linked the stimulation site, the rapid self-report, and the comparison with the sham procedure within a single experiment. This type of self-report could provide a signal for selecting a stimulation site during the procedure.