A new kind of brain implant is giving hope to people living with chronic pain that conventional treatments cannot relieve. The device not only monitors brain activity but also delivers stimulation precisely when pain signals appear, offering a level of personalisation never achieved before in this field.
Chronic pain affects an estimated 20 per cent of adults in the United States. For many, standard treatments such as medication or physical therapy provide little or no relief. This is partly because chronic pain does not arise from a single location in the brain. Instead, it is the product of complex brain circuitry, which varies from one person to the next. Until now, most deep brain stimulation (DBS) therapies have relied on a “one size fits all” approach, applying stimulation in a fixed manner, regardless of individual differences. The results have been inconsistent, and the treatment often loses effectiveness over time.
Researchers at the University of California, San Francisco, set out to test whether a customised approach might work better. Six volunteers with intractable chronic pain underwent a detailed mapping process known as intracranial electroencephalography. Electrodes were placed in 14 regions of the brain and monitored for ten days. This allowed the team to track how each person’s brain responded during moments of intense pain compared with moments of relative comfort.
Once these personal patterns were identified, permanent DBS electrodes were implanted. Unlike earlier systems that provide constant stimulation, these implants were programmed to activate only when pain-related activity appeared in the brain. They also switched off during sleep, preventing unnecessary stimulation. Machine learning helped the system distinguish between brain activity linked to high pain and that linked to low pain.
After six months of fine-tuning, the devices were put to the test. Each participant completed a double-blind trial where they received three months of genuine stimulation and three months of sham stimulation, without knowing which was which. The sham treatment delivered low-frequency pulses in non-optimal locations. Throughout the trial, participants reported their pain levels several times a day.
The results were striking. Real stimulation reduced daily pain intensity by about 50 per cent. In contrast, sham stimulation caused a slight increase in reported pain. Participants also became more active, with daily step counts rising by 18 per cent during true stimulation compared with only 1 per cent during the sham phase. In addition, many reported fewer symptoms of depression and a marked improvement in their ability to carry out everyday activities.
One participant, who had not been able to hug his wife for years because of unrelenting pain, regained enough function to do so after receiving the implant. Even those who experienced only modest reductions in pain reported meaningful improvements in quality of life, which the researchers considered significant enough to continue treatment.
Importantly, these benefits lasted. Over a follow-up period of three and a half years, participants maintained their improvements without the loss of effectiveness that has hampered earlier DBS systems. The researchers believe this durability is due to the adaptive design, which delivers stimulation only when needed, avoiding the brain’s tendency to adapt to constant input.
Despite the promise, challenges remain. Scaling up this highly individualised approach will be expensive and complex, and the procedure itself is invasive. Future research will need to explore whether similar results can be achieved with less invasive forms of neuromodulation. Still, for people whose lives have been dominated by severe pain, the findings mark a major step forward.
As senior researcher Philip Denison put it, the next phase will be to directly compare adaptive stimulation with continuous stimulation to measure outcomes, while also addressing economic barriers. Nevertheless, the success of this small trial suggests that personalised brain implants could one day transform the treatment of chronic pain.
Reference: medRxiv DOI: 10.1101/2025.08.11.25333010
