Our fascination with sleep is universal and ancient. One of my favorite images from Greek mythology appears repeatedly in the cameo brooches of the Victorian era. It shows the goddess of night, Nyx, with a baby on each shoulder. One is her son Hypnos, the god of sleep and the other Thanatos, the god of death. Poppies (from which mankind has always generated a sedative) and an owl, herald of the night, often appear in the scene. I remember the first time I saw a mural of Nyx and her twin boys in the office of a particularly charming anesthesiologist. He saw his work as presiding over the patient in the operating room not only to produce profound sleep, but with careful modulation of the anesthetic, guarding him against its brother, death.
In the modern era, our interest in why we sleep, what happens during sleep and what troubles our sleep, particularly as we age, has persisted. But, unlike the ancient Greeks, we now have some answers. For example, one of the most important things that happens during sleep is a processing of all the memories of our experience during the day, erasing some that are harmful or disturbing and preparing others for long-term residence in the brain. Over 40 years ago, Crick and Mitchison described the winnowing out during sleep of disorganized signals the day’s events have produced. In an active process which they called “reverse learning, the brain discards unimportant or distorted remnants of our experience” [i] They emphasized that this is not the same as simple forgetting. This winnowing out of disorganized or harmful signals happens during rapid eye movement sleep (REM), and the dreams that are so abundant during this time (which we never remember) are the manifestations of this pruning of connections between neurons that are harmful or useless. Shuntaro Izawa and his colleagues in Japan have just shown that special melatonin concentrating hormone neurons are involved in the process.[ii] Active production of melatonin, the hormone produced by the pineal gland deep in the center of the brain, begins as daylight fades and promotes our descent into sleep. It is this concentration of melatonin in the hypothalamus that erases the fragmented, fantastical dreams produced during REM sleep. Izawa calls this “active forgetting”. One wonders if this particular mechanism in the brain could be harnessed to erase what we do not want to remember and to forget the past experiences that trouble us most.
 Crick F and Mitchison G. The function of dream sleep. Nature 304:111-114.1983.
 Izawa S, Chowdhury S, Miyazaki T et al. REM sleep-active MCH neurons are involved in forgetting hippocampus-dependent memories. Science.365:1308-1313.
Dr. Marianne Legato, Professor Emerita of Clinical Medicine at Columbia University is an internationally known academic physician, author, lecturer, and specialist in gender-specific medicine. She is founding member of the International Society for Gender Medicine and also the founder and director of The Partnership for Gender-Specific Medicine at Columbia University and its next iteration, The Foundation for Gender-Specific Medicine. These enterprises are the first collaborations between academic medicine and the private sector focused solely on gender-specific medicine: the science of how normal human biology differs between men and women and of how the diagnosis and treatment of disease differs as a function of gender and sex. Her ground breaking textbook on Gender-and Sex Specific Medicine has been published in 2017 in the 3rd edition.
She has published extensively on Gender and Sex Specific Medicine, both scientifically and for the lay public. She is also the founding editor of the journal Gender Medicine, and the Journal Gender and Genome, published for the scientific community. In 1992, Dr. Legato won the American Heart Association’s Blakeslee Award for the best book written for the lay public on cardiovascular disease. She is a practicing internist in New York City and has been listed each year in New York Magazine’s “Best Doctors” since the feature’s inception in 1993.