Early studies attempting to untangle the neurological basis of sleep typically removed or injured part of an animal’s brain to measure the effects. The results implicated a region called the basal forebrain in inducing sleep, yet some studies indicated that it was important for arousal. “The impression is that maybe in that region there’s a mixture of mechanisms,” says Yang Dan, a neurobiologist at the University of California, Berkeley. “But that’s not a very satisfactory answer.”
Dan sought to identify which cells in the basal forebrain promote which brain state. The region contains three main types of neurons: cholinergic, glutamatergic, and GABAergic. Dan and her colleagues further classified the GABAergic neurons into those containing somatostatin (SOM+) or parvalbumin (PV+).
The researchers optogenetically activated each of these four cell types in mice to locate them and track their activity. The cholinergic, glutamatergic, and PV+ GABAergic neurons typically fired multiple times per second when the mice were awake or in REM sleep, but less often during non-REM sleep, a sleep stage in which the brain is less aroused overall. In contrast, non-REM sleep was when the SOM+ GABAergic neurons were most active.
Read more from The Scientist | March 1st, 2016: https://www.the-scientist.com/sleep-circuit-33948