Need deep-brain cleansing?
The mystery of sleep has fascinated neurobiologists for decades. The fundamental question is what is the purpose of sleep? Findings in a new study by Lulu Xie et al. 2013 suggests that one purpose of sleep might be to clear neurotoxic waste that accumulates in the brain during daily activity. Skeletal muscle senses overuse differently than the brain does. The brain detects increased levels of metabolites and mental fatigue ensues, ultimately leading to sleep which lowers the levels back down to baseline. The physiologic mechanism allowing metabolite clearance from the brain may be regulated in part by fluctuating volumes of cerebral spinal fluid (illustrated below).
Figure: cerebral spinal fluid volume varies during sleep and awake states. Source Sleep It Out (Suzana Herculano-Houzel).
Mentally fatigued and fuzzy thinking? Best hit the hay and wake-up in the morning with a clear head on your shoulders.