Green light induces antinociception via visual-somatosensory circuits

Light has been shown to relieve pain, but the underlying neural mechanisms remain unknown. Here, we show that low-intensity (200 lux) green light treatment exerts antinociceptive effects through a neural circuit from the visual cortex projecting to the anterior cingulate cortex (ACC) in mice. Specifically, viral tracing, in vivo two-photon calcium imaging, and fiber photometry recordings show that green light activated glutamatergic projections from the medial part of the secondary visual cortex (V2M^Glu) to GABAergic neurons in the ACC, which drives inhibition of local glutamatergic neurons (V2M^Glu→ACC^GABA→Glu). Optogenetic or chemogenetic activation of the V2M^Glu→ACC^GABA→Glu circuit mimics green-light-induced antinociception in both neuropathic and inflammatory pain model mice. Artificial inhibition of ACC-projecting V2M^Glu neurons abolishes the antinociception induced by green light. Taken together, our study shows the V2M-ACC circuit as a potential candidate mediating green-light-induced antinociceptive effects.