Researchers id brain's 'sleep switch' - Scientists activated the neuron cells using a laser light beam to make them fire in mice, a process called optogenetics. When the VLPO cells are stimulated 1 to 4 times per second, they fire each time they are stimulated, resulting in sleep.

See the source article by following the link below:
Researchers id brain's 'sleep switch' - Scientists activated the neuron cells using a laser light beam to make them fire in mice, a process called optogenetics. When the VLPO cells are stimulated 1 to 4 times per second, they fire each time they are stimulated, resulting in sleep.