Light-Sensitive Brain Cells Keep you Awake

Neurons that arouse response to light affect our ability to sleep

(RxWiki News) Bright light is often credited for arousing us and keeping us awake.  It is even known to have an antidepressant effect. But if light is responsible for arousing us, is darkness to blame for make us sleepy? 

We often hide behind sleeping masks and room-darkening curtains to avoid bright natural light. New research indicates that certain brain neurons are responsible for our reaction to light - and may be keeping us awake.

"For better sleep, avoid sleeping with the television on."

Jerome Siegel, a professor of psychiatry at the Semel Institute for Neuroscience and Human Behavior at UCLA, and colleagues have identified a group of neurons that dictate whether or not light arouses us. The team looked at the behavior of mice after genetically disabling their hypocretin, a neurotransmitter at the base of the brain responsible for body temperature, hunger, thirst and fatigue.

The researchers tested these mice along with normal mice while performing a variety of activities during both light and dark phases. The mice who didn't have hypocretin were unable to stay awake in the light and perform for reward. However, during the dark phase, these mice were unimpaired and learned at the same rate as the normal mice with hypocretin. In the normal mice, their hypocretin was activated during the light phase, but not in the dark.

"The findings suggest that administering hypocretin and boosting the function of hypocretin cells will increase the light-induced arousal response," Siegel said. "Conversely, blocking their function by administering hypocretin receptor blockers will reduce this response and thereby induce sleep." He added that hypocretin may also have antidepressant properties.

Prior research by the same team had found that hypocretin was responsible for narcolepsy and the sleepiness associated with Parkinson's disease. However, until now, the neurotransmitter's role in normal behavior was unclear.

The research was supported by the National Institutes of Health and the Medical Research Service of the Department of Veterans Affairs, and was published in the November 2011 issue of Journal of Neuroscience. 

Review Date: 
November 8, 2011