
David Edward Martin
63.8K posts





THE SUNRISE IS THE MOST POTENT CIRCADIAN STIMULUS. A 2020 paper published in Current Biology identified a previously unknown retinal circuit explaining precisely why the spectral contrast of sunrise so powerfully entrains the circadian system. The key neuron is the M1 intrinsically photosensitive retinal ganglion cell (ipRGC), which projects directly to the suprachiasmatic nucleus (SCN), the brain’s master circadian pacemaker. In primates, M1 ipRGCs are wired to perform a spectral comparison between yellow/red and blue light via two simultaneous pathways. ***This cone-based circuit is just one of several mechanisms by which morning light entrains the circadian system. Going outside after sunrise still delivers meaningful melanopsin stimulation as overall irradiance builds, and that sustained signal remains highly beneficial. The spectral contrast mechanism described here is simply the most precisely tuned and potent stimulus the system has, one that outdoor morning light delivers far more effectively than any indoor environment. As yellow and red wavelengths increase at sunrise, L and M cones drive LM-ON bipolar cells, which directly excite the M1 ipRGC. Simultaneously, the relative decrease in short-wavelength light reduces S-cone activation, quieting S-ON bipolar cells, which reduces drive to a newly identified S-cone amacrine cell, releasing its inhibitory input onto the ipRGC. Disinhibition and excitation converge on the same cell simultaneously. Melanopsin, the ipRGC’s intrinsic photopigment peaking at ~480nm, is slower and requires sustained high irradiance, taking over as morning light intensity builds. The result is a temporal relay: the cone circuit delivers a rapid spectral signal at the horizon transition, then melanopsin sustains entrainment through the morning. No indoor lighting replicates this. The sunrise delivers the exact stimulus this circuit evolved over hundreds of millions of years to detect. #science #circadian #sunrise #neuroscience #biology













🎁 Birthday and 🥁 VIGIL, May 5th. Third birthday in prison! Invitation to a Vigil for Dr. #ReinerFuellmich 📣 Let the announced vigil go around the world! Let a candle burn.🕯 📍 Bremervörde, Germany 🇩🇪 📅 Date: May 5, 2026 ⏰ Time: 2:00 PM to 7:00 PM 👉🏻 t.me/MahnwacheReine…

















