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.
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.
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 melano