Lighting up the human brain at night

Most people are aware that light affects human behaviour and can be used to treat disorders such as Seasonal Affective Disorder, but now researchers from the University of Surrey and the University of Liege have found new evidence that light administered during the night immediately reduces sleepiness and boosts human brain function.

These significant findings are published in today’s issue of Current Biology.

The brain processes light information to visually represent the environment but it also detects changes in ambient light level. The latter information induces non-image forming responses mediated by neural systems partially distinct from the visual system.

In humans, light acutely improves alertness but the mechanisms and brain areas underpinning this effect were unknown. Using functional brain imaging, normal subjects were studied in darkness following exposures to white light of various durations. Although all the brain scans were acquired in the same dark conditions, brain activity (cortical attention network) in those subjected to white light was significantly increased in proportion to the duration of previous illumination. The subjects’ alertness was similarly enhanced by exposure to light.

Moreover, researchers Fabien Perrin, now at the University of Lyon, Derk-Jan Dijk of the University of Surrey and Pierre Maquet of the University of Liege also show that activity in a suprachiasmatic hypothalamic area, which includes a nucleus known in animals as the master clock, was also related to the duration of light exposures.

These findings underscore the profound effects of light on the human brain and have important implications for understanding the effects of light on human behaviour.

The study was supported by the Belgian Fondation Médicale Reine Elisabeth, the Research Fund of Ulg, the PAI/IAP Interuniversity Pole of Attraction P5/04 and by the Wellcome Trust.


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