A new study proposes the use of focused ultrasound waves targeted at the brain as a novel method to alleviate pain.

Our perception of pain can be described as a subjective experience triggered by a physical stimulus traveling from our body to the brain. The brain then processes this stimulus, resulting in unpleasant sensations. Ongoing research focuses on various techniques for pain reduction. Recently, a group of scientists examined a new, non-invasive brain-targeted technology that aims to alleviate pain without resorting to invasive surgeries or the potential side effects commonly associated with medications.

The brain plays a central role in our experience of pain, starting with interpreting the type and source of pain and culminating in the feelings of discomfort and the negative emotions accompanying the pain. The insula, an organ located beneath the cerebral cortex,  serves as a central hub for the processing of pain. The posterior part of the insula contains a "map" of the body's organs, processing information about the location, type, and intensity of pain.  Brain activity in the posterior insula, for example, can reflect pain originating from the skin or muscles. The anterior part of the insula connects the posterior part to other brain areas, particularly the amygdala, involved in processing emotions, and the anterior cingulate cortex, which plays a key role in thinking and decision-making. The anterior part of the insula is responsible for another stage in pain processing: it links physical sensations to emotional and cognitive responses. Thus, pain acquires a subjective value and can influence our decision-making processes thereafter.

 Ultrasound technology, familiar to many as a safe imaging tool, for example in prenatal tests. Ultrasound probe | Andrey Zhernovoy, Shutterstock


A Painful Heat Sensation

In a recent study published in the journal PAIN, researchers from Virginia explored the use of ultrasound waves to influence the insula directly. They hypothesized that ultrasound waves could reduce insular activity, thereby leading to a decrease in the subjective sensation of pain. The study involved 23 healthy participants who were subjected to a moderate heat pain stimulus via a hot plate attached to the back of their hand. They reported the subjective level of pain they felt, while intermittently exposed to focused ultrasound waves directed at either the anterior or posterior part of the insula, without knowledge of wave activity or target area. Researchers also monitored participants' heart rates and variability - the varying time intervals between heartbeats - as indicators of the ultrasound waves' impact on the body's response to pain. Indeed, the participants reported lower pain levels under the influence of the ultrasound waves, especially when the waves were directed at the posterior insula. Additionally, waves targeted at both parts of the insula reduced brain activity associated with pain.

Another study by researchers from France examined participants experiencing heat-induced pain on the back of the hand while measuring activity levels in the amygdala and in the anterior and posterior insula. Results showed that posterior insular activity correlated with heat intensity and remained constant throughout the experiment. In contrast, activity in the anterior insula and amygdala varied throughout the experiment. Activity in these areas significantly increased when participants reported subjective pain, irrespective of heat intensity. The findings of both experiments collectively support the hypothesis that increased activity in both the anterior and posterior insula indicates increased pain sensation, yet further research is needed for a comprehensive understanding of pain perception.

 Focusing ultrasound waves on the posterior part of the insula led to pain reduction and did not affect heart rate variability (top), whereas focusing on the anterior part did not reduce pain but affected heart rate variability. Graphical summary of the experiment | from the research article


A Seemingly Insignificant Improvement

The observed reduction in pain was close to a single point on the subjective pain scale. At first glance, this may seem relatively inconsequential. Furthermore, with only 23 participants, the study's sample size might seem small for this type of research. However, it's important to note that this preliminary investigation focused on healthy individuals exposed to moderate pain. For individuals suffering from chronic, severe pain, even marginal pain relief can markedly improve quality of life and daily functioning. Considering the adverse effects often associated with pain medications, the development of innovative interventions for such patients is paramount.

Ultrasound waves are commonly familiar to the general public, for example, from applications such as tests throughout pregnancy, in which they enable physicians to visualize fetal development in the womb. However, with precise targeting, this technology holds promise for significantly modulating brain activity.  Given their ability to deeply penetrate the brain, non-invasiveness, and capacity to either augment or diminish brain activity in the specific brain regions, ultrasound waves can offer potential solutions across various domains.