SHY hypothesis explains that sleep is the price we pay for learning

MADISON — Why do animals ranging from fruit flies to humans all need to sleep? After all, sleep disconnects them from their environment, puts them at risk and keeps them from seeking food or mates for large parts of the day. Two leading sleep scientists from the University of Wisconsin School of Medicine and Public Health say that their synaptic homeostasis hypothesis of sleep or "SHY" challenges the theory that sleep strengthens brain connections. The SHY hypothesis, which takes into account years of evidence from human and animal studies, says that sleep is important because it weakens the connections among brain cells to save energy, avoid cellular stress, and maintain the ability of neurons to respond selectively to stimuli. "Sleep is the price the brain must pay for learning and memory," says Dr. Giulio Tononi, of the UW Center for Sleep and Consciousness. "During wake, learning strengthens the synaptic connections throughout the brain, increasing the need for energy and saturating the brain with new information. Sleep allows the brain to reset, helping integrate, newly learned material with consolidated memories, so the brain can begin anew the next day. " Tononi and his co-author Dr. Chiara Cirelli, both professors of psychiatry, explain their hypothesis in a review article in today's issue of the journal Neuron. Their laboratory studies sleep and consciousness in animals ranging from fruit flies to humans; SHY takes into account evidence from molecular, electrophysiological and behavioral studies, as well as from computer simulations. "Synaptic homeostasis" refers to the brain's ability to maintain a balance in the strength of connections within its nerve cells. Why would the brain need to reset? Suppose someone spent the waking hours learning a new skill, such as riding a bike. The circuits involved in learning would be greatly strengthened, but the next day the brain will need to pay attention to learning a new task. Thus, those bike-riding circuits would need to be damped down so they don't interfere with the new day's learning. "Sleep helps the brain renormalize synaptic strength based on a comprehensive sampling of its overall knowledge of the environment," Tononi says, "rather than being biased by the particular inputs of a particular waking day." The reason we don't also forget how to ride a bike after a night's sleep is because those active circuits are damped down less than those that weren't actively involved in learning. Indeed, there is evidence that sleep enhances important features of memory, including acquisition, consolidation, gist extraction, integration and "smart forgetting," which allows the brain to rid itself of the inevitable accumulation of unimportant details. However, one common belief is that sleep helps memory by further strengthening the neural circuits during learning while awake. But Tononi and Cirelli believe that consolidation and integration of memories, as well as the restoration of the ability to learn, all come from the ability of sleep to decrease synaptic strength and enhance signal-to-noise ratios. While the review finds testable evidence for the SHY hypothesis, it also points to open issues. One question is whether the brain could achieve synaptic homeostasis during wake, by having only some circuits engaged, and the rest off-line and thus resetting themselves. Other areas for future research include the specific function of REM sleep (when most dreaming occurs) and the possibly crucial role of sleep during development, a time of intense learning and massive remodeling of brain Counselor CEUs

Alcohol, tobacco, drug use far higher in severely mentally ill

In the largest ever assessment of substance use among people with severe psychiatric illness, researchers at Washington University School of Medicine in St. Louis and the University of Southern California have found that rates of smoking, drinking and drug use are significantly higher among those who have psychotic disorders than among those in the general population. The study is published online in the journal JAMA Psychiatry. The finding is of particular concern because individuals with severe mental illness are more likely to die younger than people without severe psychiatric disorders. "These patients tend to pass away much younger, with estimates ranging from 12 to 25 years earlier than individuals in the general population," said first author Sarah M. Hartz, MD, PhD, assistant professor of psychiatry at Washington University. "They don't die from drug overdoses or commit suicide — the kinds of things you might suspect in severe psychiatric illness. They die from heart disease and cancer, problems caused by chronic alcohol and tobacco use." The study analyzed smoking, drinking and drug use in nearly 20,000 people. That included 9,142 psychiatric patients diagnosed with schizophrenia, bipolar disorder or schizoaffective disorder — an illness characterized by psychotic symptoms such as hallucinations and delusions, and mood disorders such as depression. The investigators also assessed nicotine use, heavy drinking, heavy marijuana use and recreational drug use in more than 10,000 healthy people without mental illness. The researchers found that 30 percent of those with severe psychiatric illness engaged in binge drinking, defined as drinking four servings of alcohol at one time. In comparison, the rate of binge drinking in the general population is 8 percent. Among those with mental illness, more than 75 percent were regular smokers. This compares with 33 percent of those in the control group who smoked regularly. There were similar findings with heavy marijuana use: 50 percent of people with psychotic disorders used marijuana regularly, versus 18 percent in the general population. Half of those with mental illness also used other illicit drugs, while the rate of recreational drug use in the general population is 12 percent. "I take care of a lot of patients with severe mental illness, many of whom are sick enough that they are on disability," said Hartz. "And it's always surprising when I encounter a patient who doesn't smoke or hasn't used drugs or had alcohol problems." Hartz said another striking finding from the study is that once a person develops a psychotic illness, protective factors such as race and gender don't have their typical influence. Previous research indicates that Hispanics and Asians tend to have lower rates of substance abuse than European Americans. The same is true for women, who tend to smoke, drink and use illicit drugs less often than men. "We see protective effects in these subpopulations," Hartz explained. "But once a person has a severe mental illness, that seems to trump everything." That's particularly true, she said, with smoking. During the last few decades, smoking rates have declined in the general population. People over age 50 are much more likely than younger people to have been regular smokers at some point in their lives. For example, about 40 percent of those over 50 used to smoke regularly. Among those under 30, fewer than 20 percent have been regular smokers. But among the mentally ill, the smoking rate is more than 75 percent, regardless of the patient's age. "With public health efforts, we've effectively cut smoking rates in half in healthy people, but in the severely mentally ill, we haven't made a dent at all," she said. Until recently, smoking was permitted in most psychiatric hospitals and mental wards. Hartz believes that many psychiatrists decided that their sickest patients had enough problems without having to worry about quitting smoking, too. There also were concerns about potential dangers from using nicotine-replacement therapy, while continuing to smoke since smoking is so prevalent among the mentally ill. Recent studies, however, have found those concerns were overblown. The question, she said, is whether being more aggressive in trying to curb nicotine, alcohol and substance use in patients with severe psychiatric illness can lengthen their lives. Hartz believes health professionals who treat the mentally ill need to do a better job of trying to get them to stop smoking, drinking and using drugs. "Some studies have shown that although we psychiatrists know that smoking, drinking and substance use are major problems among the mentally ill, we often don't ask our patients about those things," she said. "We can do better, but we also need to develop new strategies because many interventions to reduce smoking, drinking and drug use that have worked in other patient populations don't seem to be very effective in these psychiatric patients." CADC I & II Continuing Education ### Funding for this research comes from the National Institute on Drug Abuse (NIDA), the National Institute on Alcohol Abuse and Alcoholism (NIAAA), the National Institute of Mental Health (NIMH) and the National Cancer Institute (NCI) of the National Institutes of Health (NIH), and the American Cancer Society. NIH grant numbers R01 DA032843, R01 DA025888, U10 AA008401, UL1 RR024992, P01 CA089392, R01 MH085548, R01 MH085542, K08 DA032680-1, Kl2 RR024994, K01 DA025733. Hartz SM, Pato CN, Medeiros H, Cavazos-Rehg P, Sobell JL, Knowles JA, Bierut LJ, Pato MT and the Genomic Psychiatry Cohort Consortium. JAMA Psychiatry Published online Jan. 1, 2014. doi:10.1001/jamapsychiatry.2013.3276 Washington University School of Medicine's 2,100 employed and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation, currently ranked sixth in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC HealthCare.