Chronic pain: ‘signature’ identified in the brain

In a small group of individuals with chronic pain caused by a stroke or amputationthe so-called

Phantom limb syndrome

were first identified brain signatures of pain itself. The researchers recorded pain data from inside the brains of these individuals. One of the major obstacles encountered by scholars in the search for effective treatments for chronic pain is represented by the fact that it is a symptom – that is, a subjective entity – whose nature can only be described by those who suffer from it, while an effective cure can be undertaken only against a sign, i.e. an objective entity whose nature can be described in a concrete way, or better yet measured. Therefore, a long-sought neurophysiological goal has been to understand how the brain represents pain, then how to intervene on this representation to make the condition more tolerable of chronic pain sufferers.

But it seems that something is about to change: the results of the have just been published in Nature Neuroscience a study of patients with
neuropathic pain, which is a variant of chronic pain caused for example by a stroke or the result of an amputation. Data were collected over months on patients at home and were analyzed using electronic data collection tools. Thereby, researchers identified a brain area associated with chronic pain and objective biomarkers of chronic pain in individual patients. These results represent a first step towards the development of new methods for monitoring and treating chronic pain. “This is a great example of how the latest tools to measure brain activity can be applied to an important public health issue, namely the need to relieve severe and persistent chronic pain,” said Walter Koroshetz, director of the National Institute of Neurological Disorders & Stroke USA. “We believe these preliminary results could lead to effective and non-addictive pain-relieving treatments, as opioids do.”

Chronic pain is one of the leading causes of disability worldwide. In particular, neuropathic pain is caused by damage to the system

nervous himself. It most commonly occurs due to injury to the nerves, but in the case of the people enrolled in this study, the pain could be coming from the brain itself. This type of pain does not respond well to treatments available today and can be quite debilitating for those forced to live with it. “When you think about pain, the bottom line is that it’s one of the most devastating experiences a person can go through,” says Prasad Shirvalkar, associate professor of anesthesia and neurosurgery at the University of California San Francisco and lead author of this study. “Despite this, there is still much to understand about the physiology of pain. By developing more effective tools to study and possibly modify the brain’s responses to this condition, we hope to provide new options for people living with chronic pain.”

Typically, researchers collect data on chronic pain through self-reports of sufferers. Examples of this type of data include questionnaires about pain intensity and its emotional impact. This study, however, also looked at direct changes in brain activity in two regions thought to respond directly to pain: the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC). «The studies of functional MRI show that the ACC and OFC regions of the cortex are activated during acute pain experiments. We were also interested in seeing if these cortical regions participate in the processing of chronic pain» continues Shirvalkar. “We were particularly interested in answering questions such as the change in pain over time and which brain signals might predict high levels of chronic pain.” Four participants, three with post-stroke pain and one with phantom limb pain, were surgically implanted electrodes placed at the level of the ACC and OFC regions. Several times a day, each participant was asked to rate the pain in terms of its strength, type, and emotional implication. After each response, the recording of the activity in the cortical areas under study was started (via a remote control device). Using artificial intelligence methodsthe research team was able to use activity in the OFC region to predict participants’ chronic pain status.

In a separate comparison study, researchers looked at the responses of the ACC and OFC regions to acute pain caused by the application of skin heat. In two of the four patients, brain activity again appeared to be predictive of pain response, but in this case the region most involved seemed to be the ACC. This suggests that The brain processes acute pain differently than chronic pain, although more studies are needed since data from only two participants were used in this comparison. However, this study represents a first step towards discovering the patterns of brain activity that underlie pain perception. Identifying such a pain ‘signature’ could allow the development of new therapies that can modulate brain activity to alleviate suffering from chronic pain.