“The clearest finding is that sleep does not serve just a single purpose. Instead it appears to be needed for the optimal functioning of a multitude of biological processes—from the inner workings of the immune system to proper hormonal balance, to emotional and psychiatric health, to learning and memory, to the clearance of toxins from the brain. At the same time, none of these functions fails completely in the absence of sleep. In general, sleep seems to enhance the performance of these systems instead of being absolutely necessary. And yet anyone who lives for months without sleep will die.”—Robert Stickgold, Scientific American, October 2015
Sleep deprivation and the effects of reduced amounts of sleep are now being studied seriously at several universities. According to Robert Stickgold, director of the Center for Sleep and Cognition at Beth Israel Deaconess Medical Center, lack of sufficient sleep reduces the creation of antibodies produced by vaccination and thereby undermines their effectiveness, reduces the ability to clear glucose from the blood (the function of insulin), increases blood levels of the appetite-stimulating hormone ghrelin, and decreases the quantity of a hormone called leptin which inhibits hunger by signaling the brain that there is no need to eat. The results are increased feelings of hunger which contribute to obesity.
Other research suggests that memory fixation occurs during sleep and that with sleep deprivation we are likely to form twice as many memories of negative life events as of positive events. This results in biased, and potentially depressing, memories of the day’s events. Under certain circumstances, this can lead to major depression and may contribute to other psychiatric disorders as well.
An important finding for educators is that sleep after learning leads to the selective stabilization, strengthening, integration and analysis of new memories. In this way sleep controls what we remember and how we remember it. It also prevents the deterioration of memories over time and can actually improve them. It selectively strengthens memories that our brain deems valuable. What is valuable for the brain is information that can help enhance future performance.
Other lines of research are exploring the implications of the increase in inter-cellular space that occurs in the brain during sleep. This results in a better flow of cerebrospinal fluid between the brain and the spine. Experiments with mice demonstrate that betaamyloid (the precursor of the amyloid plaques found between neurons in the brains of Alzheimer’s patients) is cleared from the brain during sleep at twice the rate seen in awake animals.
Overall, the results of studies on the role of sleep in hormonal, immunological and memory functions suggest that a lack of sufficient sleep could result not only in being very tired, but sick, overweight, forgetful and very blue.