Scientists Use Light-Activated Drugs to Map Neural Circuits Driving Placebo Pain Relief

Researchers use light-activated drugs and mouse models to identify the brain pathways and internal painkillers that drive the placebo effect.

By: AXL Media

Published: Apr 17, 2026, 6:54 AM EDT

Source: Information for this report was sourced from University of California - San Diego

Deconstructing the Neurological Placebo Mechanism

Researchers have successfully pinpointed the internal "pharmacy" of the brain by mapping the pathways that allow expectations to translate into physical pain relief. In a study published in the journal Neuron, a team led by Matthew Banghart of UC San Diego used a "reverse translation" approach to adapt human placebo protocols for mice. This method allowed the team to deconstruct the underlying mechanisms of the placebo effect with unprecedented precision. By tracking neural activity from the cortex down to the brainstem and spinal cord, the study established how the brain’s higher-order cognitive expectations can trigger a potent, localized analgesic response.

The Critical Role of Endogenous Opioids

The study identifies the ventrolateral periaqueductal gray (vlPAG) as the essential hub for endogenous opioid signaling during placebo trials. Using novel sensors, the scientists detected the release of natural opioid neuropeptides, commonly known as endorphins, within this specific brain region. The findings confirm that the vlPAG acts as a gateway, where the brain’s self-generated signals mimic the effects of external opioid medications. This discovery provides the first definitive evidence that naturally occurring peptides are not just present during the placebo effect but are the primary drivers of the resulting pain relief.

Precision Control via Light-Activated Technology

To verify the necessity of these internal painkillers, the team employed a breakthrough technology known as PhNX, or photoactivatable naloxone. This light-activated drug allowed researchers to block opioid receptors at exact locations and times using focused light. By selectively interfering with opioid signaling in the vlPAG, the scientists demonstrated that both morphine-induced relief and placebo-driven relief were neutralized. This high-resolution manipulation proved that the placebo effect relies on the same biological "machinery" as powerful pharmaceutical narcotics, but without the systemic risks.