When I started my first research laboratory 42 years ago, one of my first actions was to replace all of the standard fluorescent light fixtures, with more natural daylight spectrum bulbs that contained more blue wavelengths. My experience, and that of research students in my laboratory, was that this made the work environment more calm and tranquil. By now we have learned that blue light is the best stimulus for a visual pathway that lies outside of the classical (red/green/blue) rod and cone photoreceptor cells of our retinas. It is driven by a the blue sensitive visual pigment, melanopsin, that is found in some newly discovered inner (ganglion) cells of the retina. Ambient light input from both this and the classical photoreceptors significantly modulates ongoing cognitive brain function, including attention, working memory, updating, and sensory processing, within a few tens of seconds. The amygdala, a central component of our emotional brain, receives sparse direct projections from the newly discovered light sensitive retinal ganglion cells and is one of the brain areas acutely affected by changes in ambient light. Vandewalle et al have now shown that ambient, particularly blue, light directly influences emotional brain processing. Their abstract:
Light therapy can be an effective treatment for mood disorders, suggesting that light is able to affect mood state in the long term. As a first step to understand this effect, we hypothesized that light might also acutely influence emotion and tested whether short exposures to light modulate emotional brain responses. During functional magnetic resonance imaging, 17 healthy volunteers listened to emotional and neutral vocal stimuli while being exposed to alternating 40-s periods of blue or green ambient light. Blue (relative to green) light increased responses to emotional stimuli in the voice area of the temporal cortex and in the hippocampus. During emotional processing, the functional connectivity between the voice area, the amygdala, and the hypothalamus was selectively enhanced in the context of blue illumination, which shows that responses to emotional stimulation in the hypothalamus and amygdala are influenced by both the decoding of vocal information in the voice area and the spectral quality of ambient light. These results demonstrate the acute influence of light and its spectral quality on emotional brain processing and identify a unique network merging affective and ambient light information.