ganglion

Its additional role, say the researchers, may shift from trash sorter to signal messenger in dorsal root ganglion neurons -- cells that convey sensory signals from nerve cells close to the skin to the central nervous system.

If short-wavelength light activates the ganglion cells, they signal to the internal clock that it is daytime.

"Rather, our results support the findings of many other studies that the light-sensitive ganglion cells are most important for the human internal clock," says the scientist.

The electrical nerve impulses are finally transmitted to ganglion cells in the retina and then via the optic nerve to the visual cortex in the brain.

"However, the light-sensitive ganglion cells also receive information from the cones. This raises the question of whether the cones, and thereby the light colour, also influence the internal clock. After all, the most striking changes in brightness and light colour occur at sunrise and sunset, marking the beginning and end of a day," says Dr. Christine Blume.