Chemical involved in awakening in the presence of light

Researchers have found a group of neurons in the hypothalamus of the brain help us in awakening.

This research is conducted by Jerome Siegel, a professor of psychiatry at the Semel Institute for Neuroscience and Human Behavior at University of California, Los Angeles (UCLA), and colleagues and is published in the recent edition of The Journal of Neuroscience.

Researchers have found that hypothalamus – an area at the base of the brain controlling involuntary actions like release of hormones, hunger, sleep, body temperature – is associated with the light-induced arousal response. Cells in this part of the brain release neurotransmitter, called as hypocretin, which is related to awakening in the presence of light.

Hypothalamus & pituitary

Researchers worked on mice and found that mice without hypocretin were unable to stay awake in light but mice with hypocretin showed intense activation of the cells in the light but didn’t show any activity in the dark.

The same researchers from UCLA previously found that reduction of hypocretin results in narcolepsy and sleepiness related to Parkinson’s diseases. Siegel said,

“This current finding explains prior work in humans that found that narcoleptics lack the arousing response to light, unlike other equally sleepy individuals, and that both narcoleptics and Parkinson’s patients have an increased tendency to be depressed compared to others with chronic illnesses,”


McGregor, R. et. al. (2011). Highly Specific Role of Hypocretin (Orexin) Neurons: Differential Activation as a Function of Diurnal Phase, Operant Reinforcement versus Operant Avoidance and Light Level. The Journal of Neuroscience, 31(43): 15455-15467.

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