Orange light helps thinking

Who needs coffee in the morning when you can just shine an orange light in your eyes? A team of European scientists has shown that exposure to an orange light improves alertness and cognitive brain function.

Light, both natural and artificial, affects our circadian rhythms, causing alertness and sometimes upsetting our sleep patterns. Scientists believe this physiological interaction with light acts through the body’s photoreception system, which relies heavily on a recently discovered light-sensitive cell or photopigment called melanopsin found within the eye. These cells work separately to the rods and cones needed for vision.

Melanopsin

Previous research on animals in the last few years has shown that, if melanopsin is absent, non-visual functions are disrupted. Their built-in biological clock becomes deregulated and ‘free runs’ independent from day-night cycles, and light no longer has a stimulating effect.

Researchers from the University of Liège, Belgium, and INSERM Stem Cell and Brain Research Institute, France, wanted to find out how melanopsin affects the human brain, what effect different wavelengths of light had on melanopsin and how this influences executive brain responses – cognitive brain functions such as anticipation, working memory, sequencing (breaking tasks into smaller units and ordering them), problem-solving and decision-making – and alertness.

Testing

The researchers put 16 young and healthy test subjects through a week of regulating their sleep/wake patterns (with approximately 8 hours of sleep each night). On the days of the experiment, participants arrived 2 hours after waking and were exposed to white light for 5 minutes to standardise their light history. The subjects than underwent consecutive and identical functional magnetic resonance imaging (fMRI) scans, during which they performed a simple auditory detection task and a more difficult auditory working memory task while continuously exposed to the same test light (green light at 515 nm).

Just over an hour before each recording, the subjects were exposed to 10-minute blasts of either blue (at 461 nm) or orange light (at 589 nm – strictly speaking, quite a yellowy orange light). They were blindfolded at all times when not undergoing light exposures or their scan and brain tasks.

Results

The researchers were able to show that executive brain responses were influenced by the wavelength of the light to which individuals were exposed some 70 minutes prior to each recording. Prior exposure to the longer wavelength orange light enhanced the subsequent impact of the test light – the subjects showed greater brain activity in several regions of the frontal lobes related to alertness and cognition – while prior exposure to the shorter wavelength blue light had the reverse outcome.

“This wavelength-dependent impact of prior light exposure is consistent with recent theories of the light-driven melanopsin dual states. Our results emphasize the critical role of light for cognitive brain responses and are, to date, the strongest evidence in favour of a cognitive role for melanopsin, which may confer a form of ‘photic memory’ to human cognitive brain function,” write the researchers in their published paper.

In a press release from INSERM, the researchers write, “Ultimately, these findings argue for the use and design of lighting systems to optimize cognitive performance.” Given melanopsin’s cognitive effects, perhaps the concept of ‘smart’ lighting systems in schools and universities has a whole new meaning.

The research was published online ahead of print on 10 March 2014 in the journal Proceedings of the National Academy of Sciences (PNAS).