Sleep is defined as a state in which the body exhibits low responsivity to external stimuli. Commonly humans spend 8 hours a day sleeping. Most animals require sleep. Biologists’ favorite experiment worm, nematode C. elegans, requires sleep. This worm has exactly 959 cells, of which 302 are neurons (brain cells) and needs about 3 sleep hours a day. Different animals spend different periods of time sleeping. Horses, the alertness record-holders, sleep about two hours a day, while the little brown bat (Myotis lucifugus), sleeps about 20 hours a day.

Sleep is crucial for human and animal health. Sleep deprivation in humans can cause high blood pressure, diabetes, heart attack, heart failure and stroke. Too little sleep can also cause obesity, depression and a lower sexual drive.

Using scientific measures we can diagnose the effects of sleep on brain activity, and even learn about the different types of hormones associated with sleep, such as melatonin and stamina that are responsible for the sleep process. Reducing the hormonal activity of serotonin and norepinephrine causes REM sleep, a deep sleep with dreams. Another hormone involved in the sleep process is cortisol, which participates in the waking process.

Sleep is also known to shape our memories. In a paper published in Nature Neuroscience journal, the researchers reported on the mechanism that allows memory design in our brains. The brain contains cells called microglia. The meaning of the word glia in Greek is glue. In the past, these cells were thought to be the adhesive bonding the neurons whom are important for brain activity. Further investigation has revealed that microglia cells are actually immune cells that respond to any sign of infection or brain damage. According to the new study, these cells are active during sleep, and treat brain damages that have occurred. During sleep their activity is more efficient. The researchers observed that when the hormone concentration of norepinephrine increases, the brain exits the REM sleep, and the microglia cells are significantly less active.

This study shows that maintenance and repair of neural circuits occur during sleep and may be partly mediated by the ability of microglia cells to dynamically interact with the brain. Finally, these findings reinforce the importance of healthy sleep.

Have a Good Night’s Rest