A top-down neural circuit for affective-motivational responses of pain relief induced by electroacupuncture.

Researchers have discovered how electroacupuncture (EA) relieves pain by activating specific brain circuits that reduce both physical discomfort and the emotional distress that comes with chronic pain. The study examined both human patients with chronic low back pain and animal models to understand how acupuncture signals travel from the body to the brain. Scientists found that electroacupuncture at the ST36 acupoint (located on the lower leg) activated a pathway between two brain regions: the infralimbic cortex and the nucleus accumbens shell. This circuit is crucial for processing emotions and motivation. In animals experiencing chronic pain, EA not only reduced pain sensitivity but also decreased anxiety and depression-like behaviors that often accompany persistent pain. The pain relief from EA created a positive emotional response, measured through preference tests where animals chose to spend time in locations where they received treatment. Importantly, this rewarding effect only occurred when animals were actually in pain—suggesting EA specifically targets pain-related suffering rather than creating a general pleasurable sensation. When researchers blocked this brain pathway, the benefits of EA disappeared, confirming its importance. Human patients with chronic low back pain showed similar improvements in emotional well-being after EA treatment. This research helps explain why acupuncture can be effective for chronic pain conditions that have both physical and psychological components, such as anxiety and depression that develop alongside persistent pain. The findings support using electroacupuncture as part of comprehensive pain management strategies. If you're considering acupuncture for chronic pain, seek treatment from a licensed acupuncturist trained in electroacupuncture techniques.

This study elucidates the neural mechanisms underlying EA-induced analgesia and affective responses in chronic pain states. Using spared nerve injury (SNI) rat models alongside human chronic low back pain patients, researchers demonstrated that 2 Hz EA at ST36 activates glutamatergic neurons in the infralimbic cortex (IL), which project to GABAergic neurons in the nucleus accumbens (NAc) shell. Methodologies included conditioned place preference (CPP), optogenetics, chemogenetics, multi-electrode array recording, and retrograde neuronal tracing. EA induced CPP exclusively in pain states, not in pain-free conditions, indicating specificity for pain-related negative affect. Optogenetic activation of ILGlu neurons replicated EA's analgesic and anxiolytic effects, while inhibition abolished them. Critically, the IL-NAc shell pathway was necessary for EA-induced analgesia, CPP, and reduction of anxiety-like behaviors. Human subjects showed corresponding improvements in affective-motivational measures via self-report questionnaires. Clinical implications suggest EA targets top-down neural circuits mediating the emotional dimension of pain, supporting its use for chronic pain with comorbid psychological symptoms. This represents a mechanistic validation of EA's role in integrated pain management.