New Research Uncovers Brain Circuit That Connects Pain and Its Emotional Impact

Pain transcends mere physical sensation; it’s intertwined with emotional experiences that can exacerbate suffering. A recent study from the Salk Institute reveals a specific brain circuit responsible for connecting physical discomfort to its emotional consequences, potentially offering new targets for managing chronic pain conditions like fibromyalgia, migraines, and PTSD.

Published in the Proceedings of the National Academy of Sciences on July 9, 2025, the research identifies a distinct group of neurons in the thalamus, challenging traditional beliefs about how pain is processed. Senior author Sung Han articulated the study's significance: "For decades, the prevailing view was that the brain processes sensory and emotional aspects of pain through separate pathways." However, their findings suggest that a portion of the sensory pain pathway also plays a crucial role in the emotional experience of pain.

This distinction is vital because it highlights why individuals experience pain differently. While most people react similarly to sensory stimuli, the emotional toll associated with pain can vary widely, with factors like anxiety and distress amplifying the suffering. If emotional responses become overly sensitive, they can lead to chronic pain disorders.

Breaking Down Pain Pathways

Traditionally, the sensory experience of pain has been understood as mediated by the spinothalamic tract, which transmits signals from the spinal cord to the thalamus and subsequently to areas responsible for sensory processing. On the flip side, affective pain was thought to rely on the spinoparabrachial tract, sending signals from the spinal cord to the brainstem.

However, the Salk team utilized advanced analytical methods to examine this complex circuitry. Their research unveiled a previously unidentified spinothalamic pathway in mice. In this new circuit, pain signals not only go to the thalamus but also connect to the amygdala, a crucial hub for emotional processing. The neurons involved express CGRP (calcitonin gene-related peptide), a neuropeptide foundational to their discoveries.

The Role of CGRP Neurons

When the researchers genetically silenced these CGRP neurons, the mice still reacted to mild pain but did not associate enduring negative feelings with it. They lacked learned fear or avoidance of pain-related situations in subsequent tests. Conversely, activating these neurons prompted distress and avoidance behaviors, even without any pain stimuli present.

This thematic shift in understanding pain points to a potential new avenue for treatment, particularly for chronic pain conditions marked by intense emotional responses. As first author Sukjae Kang notes, "Pain processing is not just about nerves detecting pain; it’s about the brain deciding how much that pain matters." Their insights might be key in addressing chronic conditions that typically resist standard medications.

Chronic Pain and Sensitivity

Chronic pain disorders like fibromyalgia and migraines are characterized by prolonged and severe pain experiences, often without a clear physical origin. Patients frequently report heightened sensitivity to stimuli that others might not find painful, such as light or sound. The team’s hypothesis involves overactivity in the CGRP pathway, suggesting that it could distort how the brain interprets sensory input.

Intriguingly, current medications that block CGRP could be explained by these findings, hinting at their effectiveness for treating migraines. This revelation may pave the way for developing new, non-addictive therapies targeted at emotional pain disorders.

Implications for Mental Health

Han also suggests that this research could hold implications for psychiatric disorders that exhibit heightened threat perception, such as PTSD. Preliminary findings from Han’s lab indicate that the CGRP-affiliated pain pathway is part of a broader brain alarm system capable of responding to multiple unpleasant sensations. By modulating this pathway through CGRP blockers, there's potential for easing symptoms of fear and hyperarousal in trauma-related conditions.

Yet, many questions remain, particularly regarding how this pathway relates to psychological pain stemming from social experiences, such as grief and loneliness. Understanding these connections may yield further insights into the emotional components of pain.

"Our discovery of the CGRP affective pain pathway gives us a molecular and circuit-level explanation for the difference between detecting physical pain and suffering from it," states Han. Their continued study of this pathway is anticipated to pave the way for advanced therapies that could significantly alleviate patient suffering.

Co-authors of the study include Shijia Liu, Jong-Hyun Kim, Dong-Il Kim, Tae Gyu Oh, Jiahang Peng, Mao Ye, Kuo-Fen Lee, Ronald M. Evans, and Martyn Goulding from Salk. Funding for the work was provided by the National Institutes of Mental Health and the Simons Foundation.

For more information, please visit the Salk Institute.