Washington: Scientists have identified brain cells that respond to bright light, secreting a substance that keeps us wake.

Jerome Siegel, Professor of psychiatry at the University of California-LA Semel Institute for Neuroscience and Human Behaviour, suggests that the cells necessary for a light-induced arousal response are located in the hypothalamus.

“These cells release a neurotransmitter (conveying signals) called hypocretin,” said Siegel.
Hypothalmus is an area at the base of the brain responsible for, among other things, control of the autonomic nervous system, body temperature, hunger, thirst, fatigue -- and sleep, according to a statement from UCLA.