How does the brain switch between wakefulness and sleep?

Typical sleep patterns in mammals are composed of two phases: non-rapid eye movement (NREM) sleep and REM (rapid eye movement) sleep or dreaming sleep. Researchers from Bern wanted to understand the mechanisms that help the brain switch between the two patterns. They identified a new neural circuit between hypothalamus and thalamus that have been associated with electroencephalogram rhythms during sleep. Making use of optogenetics, the researchers controlled the neurons from the hypothalamus with millisecond-timescale light pulses. The neurons’ brief activation during light sleep induced rapid awakenings, while their chronic activation maintained prolonged wakefulness. On the other hand, when the circuit was silenced, deep sleep was induced. They found that the hyperactivity of the circuit was possibly the cause of insomnia. Moreover, the circuit’s arousal power is strong enough to recover an organism from anesthetic state. This study, therefore, can prove important in treating patients who are in a vegetative state.

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