Exposure to bright light, especially from the sun, can cause intrinsically photosensitive retinal cells to fire action potentials for hours, signaling throughout the brain and body.

“when shown bro bright light on these intrinsically photosensitive cells you could crank up the intensity of the light and the neurons would ramp up their membrane potential and then start spiking firing action potential long trains of action potentials that have been shown to go on for hours and so that's this signal that's propagating into the whole brain and body”