Exposure to light at night lowers cognitive function: study

Researchers at Johns Hopkins University have found that regular exposure to bright lights at night can result in depression and learning impairments.

“Basically, what we found is that chronic exposure to bright light — even the kind of light you experience in your own living room at home or in the workplace at night if you are a shift worker — elevates levels of a certain stress hormone in the body, which results in depression and lowers cognitive function,” said Samer Hattar, a biology professor in the Johns Hopkins University’s Krieger School of Arts and Sciences.

His study was published Wednesday in the journal Nature.

Hattar found that mice exposed to bright light at night showed depressive-like symptoms and had higher levels of the stress hormone cortisol. The effect appears to be caused by special cells in the eye called intrinsically photosensitive retinal ganglion cells (ipRGCs), which stimulate the brain's limbic system when exposed to light.

“Mice and humans are actually very much alike in many ways, and one is that they have these ipRGCs in their eyes, which affect them the same way,” Hattar explained. "In addition, in this study, we make reference to previous studies on humans, which show that light does, indeed, impact the human brain's limbic system. And the same pathways are in place in mice."

Research published earlier this year in the journal Molecular Psychiatry found that hamsters exposed to dim artificial light at night for four weeks began showing depressive-like symptoms, such as being generally less active and showing less interesting in drinking sugary water. Within two weeks of returning to a standard light cycle, the depressive-like symptoms disappeared, suggesting the effect is completely reversible.

Watch video, courtesy of John Hopkins University, below: