Sleep is an essential human behavior thought to be implicated in newborn neural development, memory consolidation, and disposal of harmful cellular debris. The Mayo Clinic suggests that adults should aim for 7-9 hours of sleep per night, while teens and younger children require 9-13 hours for optimal brain and body health.
While the specific processes that occur during sleep are still largely unknown, scientists from the University of Rochester Medical Center and the Massachusetts Institute of Technology have uncovered important information about brain maintenance during sleep that utilizes specialized immune cells, microglia. Microglia are derived from macrophages and function in synaptic pruning, neuronal support, and immune responses.
This study suggests that microglia increase maintenance efficiency during sleep, implying that these cells can distinguish between awake and asleep brain states. Microglia have beta2 adrenergic receptors which are responsive to the hormone norepinephrine. During awake periods norepinephrine levels are high, sending microglia into a dormant state. Conversely, during sleep microglia are more active due to lower circulating levels of the hormone.
The scientists' results suggest a broader role for microglia as "surveillance" cells. The study also points to new avenues for scientific inquiry, such as how adrenergic signaling may affect or contribute to neuropathology. With all of the interesting pathways for future experimentation, it's immediately easy to see the importance sleep to maintaining proper brain function.