Chapter 14. Biological Rhythms, Sleep, and Dreaming
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by Laura Sanders After Baby V joined our team, one of the first things people would ask is, “Are you getting any sleep?” (The answer was, and is, no.) The recurring question highlights how sorely lacking sleep is for new parents. Capitalism noticed us tired parents, too: Countless products beckon exhausted families with promises of eight, 10, even 12 hours of blissful, uninterrupted sleep. You can buy special swaddles, white noise machines, swings that sway like a moving car and books upon books that whisper contradictory secrets of how to get your baby to sleep through the night. (If you don’t have time to read them all, mother-of-twins Ava Neyer helpfully breaks down all of the advice for you.) As the owner of a stack of such books, I was intrigued by this recent review: “Behavioral sleep interventions in the first six months of life do not improve outcomes for mothers or infants: A systematic review.” Excuse me? The Sleep Sheep, the Baby Whisperer and the Sleep Lady lied to me? At the behest of the United Kingdom’s National Institute for Health Research, Australians Pamela Douglas and Peter Hill combed through the existing scientific literature on sleep interventions looking for benefits. These interventions included delaying responses to infant cues (also known by its cold-hearted name of “crying it out”), sticking to a feeding or sleeping schedule and other ways that aim to teach a baby how to fall asleep without the need to eat or be held. After analyzing 43 studies on infant sleep interventions, the team concluded that these methods weren’t beneficial for babies younger than six months, or their mothers. The studies didn’t convincingly show that interventions curb infant crying, prevent sleep or behavioral problems later or protect against maternal depression, Douglas and Hill write in the September Journal of Developmental & Behavioral Pediatrics. © Society for Science & the Public 2000 - 2013.
by Andy Coghlan Swifts are said to spend most of their lives airborne, but no one has ever proved this. Now, a study suggests there's some truth to it: alpine swifts spend more than six consecutive months aloft, not even resting after migrating to north Africa following their breeding season in Europe. "Up to now, such long-lasting locomotive activity had been reported only for animals living in the sea," says Felix Liechti of the Swiss Ornithological Institute in Sempach. Liechti and his colleagues attached 1.5-gram data loggers to three alpine swifts (Tachymarptis melba) at a Swiss breeding site, and recaptured the birds the following year. The loggers recorded the birds' acceleration and geographic location. The measurements suggest that for 200 days, all three swifts remained airborne while migrating to and wintering in Africa. Liechti says researchers have previously asserted but never proved that newborn common swifts spend three years aloft before landing for breeding. "Amazing, truly amazing," says Carsten Egevang of the Greenland Institute of Natural Resources in Nuuk of Liechti's findings. "We knew that swifts stay on the wing for long periods, but 200 days is very impressive." The birds survive on airborne plankton, and almost certainly sleep on the wing too, Liechti says. "It has been assumed that the birds 'sleep' only for seconds, or use only one half of the brain while the other half is resting," he says. © Copyright Reed Business Information Ltd
Link ID: 18767 - Posted: 10.09.2013
by Ed Yong I’ve just arrived home from 14 hours of flying. The clocks on my phone and laptop have been ticking away the whole time, and it takes a few seconds to reset them to British time. The clocks in my body are more difficult. We run on a daily 24-hour body clock, which controls everything from our blood pressure to our temperature to how hungry we feel. It runs on proteins rather than gears. Once they’re built, these proteins stop their own manufacture after a slight delay, meaning that their levels rise and fall with a regular rhythm. These timers tick away inside almost all of our cells, and they’re synchronised by a tiny collection of 10,000 neurons at the bottom of our brain. It’s called the suprachiasmatic nucleus (SCN). It’s the master clock. It’s the conductor that keeps the orchestra in sync. The SCN is also sensitive to light. It gets signals from our eyes, which allows it to synchronise its ticking with the 24-hour cycle of day and night outside. The SCN is what connects the rhythms of our bodies with those of the planet. But when we travel far and fast, and suddenly land in a new time zone, the SCN becomes misaligned with the environment. It takes time to re-adjust, typically one day for every time zone crossed. In the meantime, our sleep is disrupted and our physiology goes weird. In other words: jet lag. But at Kyoto University, Yoshiaki Yamaguchi and Toru Suzuki have engineered mice that break this rule. They are, with apologies for the awful word, unjetlaggable. If you change the light in their cages to mimic an 8-hour time difference, they readjust almost immediately. Put them on a red-eye flight from San Francisco to London and they’d be fine.
Answer by Paul King, computational neuroscientist: The emerging view in neuroscience is that dreams are related to memory consolidation happening in the brain during sleep. This may include reorganizing and recoding memories in relation to emotional drives as well as transferring memories between brain regions. During the day, episodic memories (memories for events) are stored in the hippocampus, a region of the brain specialized for long-term memory that learns particularly quickly. At night, memories from this region appear to be transferred to the cerebral cortex, the region specialized for information processing, cognition, and knowledge. Studies in animals have found that during sleep, the neural activity of the hippocampus "replays" the events of the day. This replay happens faster than real-time, and sometimes happens in reverse. The activity replay is correlated with neural activity patterns in both the visual cortex (responsible for visual experience) and the prefrontal cortex (responsible for strategy, goals, and planning). The memory replay occurs during REM sleep and dreaming. Philosopher Daniel Dennett proposes the Dream Weaving party game: One person, the Dream Guesser is asked to leave the room, and while away, someone will share a dream with the group. When the Dream Guesser returns, their job will be to ask yes/no questions of random people in the group to attempt to reconstruct the plot of the dream. © 2013 The Slate Group, LLC.
Link ID: 18744 - Posted: 10.05.2013
by Linda Geddes They say the early bird catches the worm, but night owls may be missing far more than just a tasty snack. Researchers have discovered the first physical evidence of structural brain differences that distinguish early risers from people who like to stay up late. The differences might help to explain why night owls seem to be at greater risk of depression. Around 10 per cent of people qualify as morning people or larks, and a further 20 per cent are night owls – with the rest of us falling somewhere in between. Your lark or night owl status is called your chronotype. Previous studies have suggested that night owls experience worse sleep, more tiredness during the day and consume greater amounts of tobacco and alcohol. This has prompted some to suggest that they are suffering from a form of chronic jet lag. To investigate further, Jessica Rosenberg at RWTH Aachen University in Germany and colleagues used diffusion tensor imaging to scan the brains of 16 larks, 23 night owls and 20 intermediate chronotypes. They found a reduction in the integrity of night owls' white matter – brain tissue largely comprised of fatty insulating material that speeds up the transmission of nerve signals – in areas associated with depression. "We think this could be caused by the fact that late chronotypes suffer from this permanent jet lag," says Rosenberg, although she cautions that further studies are needed to confirm cause and effect. © Copyright Reed Business Information Ltd.
By Tina Hesman Saey The sun exerts hegemony over biological rhythms of nearly every organism on Earth. But two studies now show the moon is no slouch. It controls the cadence of at least two different biological clocks: one set by tides and the other by moonlight. The clocks, both discovered in sea creatures, work independently of the circadian clock, which synchronizes daily rhythms with the sun. The studies demonstrate that the moon’s light and its gravitational pull, which creates tides, can affect the behavior of animals. “The moon has an influence, definitely,” says Steven Reppert, a neurobiologist at the University of Massachusetts Medical School in Worcester, who was not involved with either study. “Clearly for these marine organisms, it’s very powerful and important.” Scientists established decades ago that circadian clocks govern people’s daily cycles of such things as hormone levels, blood pressure and body temperature. Nearly every organism, including single-celled creatures, has some version. Circadian clocks are composed of protein gears. In a loop that takes roughly 24 hours, levels of some proteins rise and then fall, while others fall and then rise. Sunlight sets the clocks, but once a clock is set it will keep running, even when scientists keep organisms in constant darkness. © Society for Science & the Public 2000 - 2013
Keyword: Biological Rhythms
Link ID: 18714 - Posted: 09.28.2013
Few features of child-rearing occupy as much parental brain space as sleep, and with it the timeless question: Is my child getting enough? Despite the craving among many parents for more sleep in their offspring (and, by extension, themselves), the purpose that sleep serves in young kids remains something of a mystery—especially when it comes to daytime naps. Do they help children retain information, as overnight sleep has been found to do in adults? A study published today in the Proceedings of the National Academy of Sciences provides the first evidence that daytime sleep is critical for effective learning in young children. Psychologist Rebecca Spencer of the University of Massachusetts (UMass), Amherst, had more than a passing interest in the subject: Her daughters were 3 and 5 when she began chasing answers to these questions. She also wondered about growing enthusiasm for universal public preschool, where teachers don’t necessarily place much emphasis on naps. “There is a lot of science” about the best curriculum for preschool classrooms, “but nothing to protect the nap,” Spencer says. Still, data to support a nap’s usefulness were scarce: Studies in adults have found that sleep helps consolidate memories and learning, but whether the same is true of brief naps in the preschool set was unknown. So Spencer approached the first preschool she could think of that might help her find out: her daughters’. She later added other local preschools to her sample, for a total of 40 children ranging from nearly 3 to less than 6 years old. The goal of Spencer, her graduate student Laura Kurdziel, and undergraduate Kasey Duclos of Commonwealth Honors College at UMass, was to compare each child against him or herself: How well did a child learn when she napped, and what happened when she didn’t? © 2012 American Association for the Advancement of Science
By Laura Sanders A nap can ease the burden of a painful memory. While fast asleep, people learned that a previously scary situation was no longer threatening, scientists report September 22 in Nature Neuroscience. The results are the latest to show that sleep is a special state in which many sorts of learning can happen. And the particular sort of learning in the new study blunted a fear memory, a goal of treatments for disorders such as phobias and post-traumatic stress disorder. “It’s a remarkable finding,” says sleep neuroscientist Edward Pace-Schott of Harvard Medical School and Massachusetts General Hospital. Researchers led by Katherina Hauner of Northwestern University’s Feinberg School of Medicine first taught 15 (awake) volunteers to fear the combination of a face and odor. Participants saw a picture of a certain man’s face and at the same time smelled a distinctive scent, such as lemon. This face-odor combo was paired with a nasty shock, so that the volunteers quickly learned to expect something bad when they saw that particular face and smelled the associated odor. Then the volunteers tucked in for a nap in the laboratory. When the participants hit the deepest stage of sleep, called slow-wave sleep, Hauner and her colleagues redelivered the smell that had earlier come with a shock. During the nap, some participants had learned that the smell was safe. The volunteers sweated less (a measure of fear) when the face-odor combination appeared after the nap, the scientists found. When the odor wasn’t presented during sleep, volunteers’ responses to the associated face were unchanged. © Society for Science & the Public 2000 - 2013
By Melissa Healy It's a question that has long fascinated and flummoxed those who study human behavior: From whence comes the impulse to dream? Are dreams generated from the brain's "top" -- the high-flying cortical structures that allow us to reason, perceive, act and remember? Or do they come from the brain's "bottom" -- the unheralded brainstem, which quietly oversees such basic bodily functions as respiration, heart rate, salivation and temperature control? At stake is what to make of the funny, sexual, scary and just plain bizarre mental scenarios that play themselves out in our heads while we sleep. Are our subconsious fantasies coming up for a breath of air, as Sigmund Freud believed? Is our brain consolidating lessons learned and pitching out unneeded data, as neuroscientists suggest? Or are dreams no more meaningful than a spontaneous run of erratic heartbeats, a hot flash, or the frisson we feel at the sight of an attractive passer-by? A study published this week in the journal Brain suggests that the impulse to dream may be little more than a tickle sent up from the brainstem to the brain's sensory cortex. The full dream experience -- the complex scenarios, the feelings of fear, delight or longing -- may require the further input of the brain's higher-order cortical areas, the new research suggests. But even people with grievous injury to the brain's prime motivational machinery are capable of dreams, the study found.
Link ID: 18642 - Posted: 09.14.2013
Scientists believe they have discovered a new reason why we need to sleep - it replenishes a type of brain cell. Sleep ramps up the production of cells that go on to make an insulating material known as myelin which protects our brain's circuitry. The findings, so far in mice, could lead to insights about sleep's role in brain repair and growth as well as the disease MS, says the Wisconsin team. The work is in the Journal of Neuroscience. Dr Chiara Cirelli and colleagues from the University of Wisconsin found that the production rate of the myelin making cells, immature oligodendrocytes, doubled as mice slept. The increase was most marked during the type of sleep that is associated with dreaming - REM or rapid eye movement sleep - and was driven by genes. In contrast, the genes involved in cell death and stress responses were turned on when the mice were forced to stay awake. Precisely why we need to sleep has baffled scientists for centuries. It's obvious that we need to sleep to feel rested and for our mind to function well - but the biological processes that go on as we slumber have only started to be uncovered relatively recently. Dr Cirelli said: "For a long time, sleep researchers focused on how the activity of nerve cells differs when animals are awake versus when they are asleep. "Now it is clear that the way other supporting cells in the nervous system operate also changes significantly depending on whether the animal is asleep or awake." The researchers say their findings suggest that sleep loss might aggravate some symptoms of multiple sclerosis (MS), a disease that damages myelin. BBC © 2013
Charlie Cooper Scientists have moved a step closer to creating a specialist pill for jet lag, after research in mice revealed a possible mechanism for speeding up the body's natural response to moving across time zones. Researchers at the University of Oxford found they could improve the recovery time of mice exposed to irregular patterns of light and dark by blocking a particular gene in the brain, responsible for regulating the body's internal clock. Nearly all living things have an internal, subcellular mechanism - known as the circadian clock - that synchronises a variety of bodily functions to the 24-hour rhythm of the Earth's rotation. The circadian clock is regulated by a number of stimuli - chief among them light detected by the eye. But when daily patterns of light and dark are disrupted - as when we travel across several time-zones - the body clock falls out of synch, resulting in several days of fatigue and discomfort as our cells adjust to new daily patterns - experienced by long-haul fliers as jet lag. The body takes about one day to adjust for every time zone crossed. To understand the effect this has on the brain, researchers at the University of Oxford exposed mice to irregular patterns of light and dark to simulate moving across time zones. They monitored the activity of genes in the part of the brain responsible for setting the circadian clock - the suprachiasmatic nuclei (SCN) and observed that hundreds of genes were activated by light detected from the eye, all of which helped the body adjust to a new day-night rhythm. © independent.co.uk
Keyword: Biological Rhythms
Link ID: 18590 - Posted: 08.31.2013
Brain scans of people who say they have insomnia have shown differences in brain function compared with people who get a full night's sleep. Researchers at the University of California, San Diego, said the poor sleepers struggled to focus part of their brain in memory tests. Other experts said that the brain's wiring may actually be affecting perceptions of sleep quality. The findings were published in the journal Sleep. People with insomnia struggle to sleep at night, but it also has consequences during the day such as delayed reaction times and memory. The study compared 25 people who said they had insomnia with 25 who described themselves as good sleepers. MRI brain scans were carried out while they performed increasingly challenging memory tests. One of the researchers, Prof Sean Drummond, said: "We found that insomnia subjects did not properly turn on brain regions critical to a working memory task and did not turn off 'mind-wandering' brain regions irrelevant to the task. "This data helps us understand that people with insomnia not only have trouble sleeping at night, but their brains are not functioning as efficiently during the day." BBC © 2013
By MIKE STOBBE / AP Medical Writer ATLANTA (AP) — Can’t get enough shuteye? Nearly 9 million U.S. adults resort to prescription sleeping pills — and most are white, female, educated or 50 or older, according to the first government study of its kind. But that’s only part of the picture. Experts believe there are millions more who try options like over-the-counter medicines or chamomile tea, or simply suffer through sleepless nights. ‘‘Not everyone is running out to get a prescription drug,’’ said Russell Rosenberg, an Atlanta-based sleep researcher. The Centers for Disease Control and Prevention study was based on interviews with about 17,000 adults from 2005 through 2010. Study participants were even asked to bring in any medicines they were taking. Overall, 4 percent of adults said they'd taken a prescription sleeping pill or sedative in the previous month. The study did not say whether use is increasing. But a CDC researcher calculated that use rose from 3.3 percent in 2003-2006 to 4.3 percent in 2007-2010. That echoes U.S. market research — as well as studies in some other countries — that indicate an increase in insomnia in recent decades. ‘‘Sleep disorders overall are more prevalent than what they were,’’ said Dr. Ana Krieger, medical director of New York’s Weill Cornell Center for Sleep Medicine. © 2013 NY Times Co.
Link ID: 18588 - Posted: 08.31.2013
By GRETCHEN REYNOLDS As a clinical psychologist and sleep researcher at the Feinberg School of Medicine at Northwestern University, Kelly Glazer Baron frequently heard complaints from aggrieved patients about exercise. They would work out, they told her, sometimes to the point of exhaustion, but they would not sleep better that night. Dr. Baron was surprised and perplexed. A fan of exercise for treating sleep problems, but also a scientist, she decided to examine more closely the day-to-day relationship between sweat and sleep. What she and her colleagues found, according to a study published last week in The Journal of Clinical Sleep Medicine, is that the influence of daily exercise on sleep habits is more convoluted than many of us might expect and that, in the short term, sleep might have more of an impact on exercise than exercise has on sleep. To reach that conclusion, Dr. Baron and her colleagues turned to data from a study of exercise and sleep originally published in 2010. For that experiment, researchers had gathered a small group of women (and one man) who had received diagnoses of insomnia. The volunteers were mostly in their 60s, and all were sedentary. Then the researchers randomly assigned their volunteers either to remain inactive or to begin a moderate endurance exercise program, consisting of three or four 30-minute exercise sessions a week, generally on a stationary bicycle or treadmill, that were performed in the afternoon. This exercise program continued for 16 weeks. At the end of that time, the volunteers in the exercise group were sleeping much more soundly than they had been at the start of the study. They slept, on average, about 45 minutes to an hour longer on most nights, waking up less often and reporting more vigor and less sleepiness. Copyright 2013 The New York Times Company
Link ID: 18575 - Posted: 08.28.2013
By Eleanor Bradford BBC Scotland Health Correspondent More than half of all teenagers may be sleep deprived, according to experts. A combination of natural hormone changes and greater use of screen-based technology means many are not getting enough sleep. Research has suggested teenagers need nine hours' sleep to function properly. "Sleep is fundamentally important but despite this it's been largely ignored as part of our biology," said Russell Foster, Professor of Circadian Neuroscience at Oxford University. "Within the context of teenagers, here we have a classic example where sleep could enhance enormously the quality of life and, indeed, the educational performance of our young people. "Yet they're given no instruction about the importance of sleep and sleep is a victim to the many other demands that are being made of them." At One Level Up, an internet cafe and gaming centre in Glasgow, I found a group of young people who are used to very late nights. "There's things called 'grinds' which we have on Saturdays which are an all-nighter until 10 in the morning," said 17-year-old Jack Barclay. "We go home, sleep till 8pm at night and then do the exact same thing again. I like staying up." Fourteen-year-old Rachel admitted occasionally falling asleep in class because she stayed up late at night playing computer games. "If it's a game that will save easily I'll go to bed when my mum says, 'OK you should probably get some rest', but if it's a game where you have to go to a certain point to save I'll be like, 'five more minutes!' and then an hour later 'five more minutes!', and it does mess up your sleeping pattern. BBC © 2013
By Geoffrey Mohan If you can’t quite get that nine-note treble opening to "Fur Elise," just sleep on it. The brain will rehearse, reorganize and nail the sequential motor tasks that help you play piano or type on a keyboard. How that consolidation of memory happens has remained largely a mystery, despite telling evidence that the brain’s motor cortex appears to be quite busy during sleep. Now, a team led by Brown University neuroscientists believes it has found the source of the sleeping piano lesson, and it’s not where many expected it to be. Neuroscience has been fixated since its founding on why the brain “needs” that peculiar mix of dormancy and random activity known as sleep. And it equally wondered why we emerge from it better able to do things. Slowly, evidence accrued that we were “learning” during sleep -- consolidating memory in ways that would make waking tasks more successful. It seemed deepest sleep, not the familiar rapid-eye-movement type, had the most effect on our brain’s abilty to reorganize and prepare to perform better in waking hours. “It has been very difficult to measure brain activation during sleep,” said Brown University neuroscientist Masako Tamaki, lead author of the study published online Tuesday in the Journal of Neuroscience. “So it was unclear what brain region was involved.”
by Douglas Main, LiveScience Staff Writer Rock-a-bye owlet, in the treetop … Baby owls and baby mammals, including humans, sleep in an analogous manner, spending a similar amount of time in an awakelike phase called REM (rapid-eye movement), in which dreams are thought to occur, at least during adulthood, new research suggests. In both owls and humans, REM sleep decreases with increasing age. Baby humans spend about 50 percent of their snooze time in this REM phase, whereas that figure decreases to less than 25 percent in adults, according to a statement from the Max Planck Institute for Ornithology. (Applying the REM term to owls, whose eyes are fixed in their heads, may seem a stretch, but researchers use the phrase anyway.) In the new study, published in July in the journal Frontiers in Zoology, the researchers attached electroencephalograms (EEGs) and movement data loggers to 66 young barn owls to record how much time the animals spent in REM sleep and how much they moved while snoozing. They later removed the EEGs, which measure brain waves, and found that the birds mated normally and didn't appear to have suffered any negative effects from the devices, the statement noted. (7 Ways Animals Act Like Humans) "During this sleep phase, the owlets' EEG showed awakelike activity, their eyes remained closed, and their heads nodded slowly," said University of Lausanne researcher Madeleine Scriba in the statement. © 2013 Discovery Communications, LLC.
By Scicurious It’s something we feel we’ve always known: if you can’t sleep, you need to exercise more. Wear yourself out, make yourself good and tired, you’ll sleep like a baby! So when I started having trouble sleeping, I just figured I needed to work out more. Of course, it kind of figures that often, you have trouble sleeping because of life stress, which often means you’re really busy, which in turn means it probably puts MORE stress in your life just trying to find the time to work out. But that’s just details. So sometimes, when I catch myself constantly waking up in a panic over several days, I’ll fit in some hard exercise. Maybe I’ll go for a long run, or try a really hard new class or something. By the time I go to bed I am WIPED. Physically and mentally. My body is so exhausted that the feeling of lying down is one of total bliss. …so why can’t I SLEEP?!?! Turns out I was suffering under expectations that were a little too high for reality. First off, we’re not wrong. Exercise DOES improve sleep. It does. But not necessarily immediately. And perhaps, instead, we should ask a different question. Instead of asking how exercise impacts sleep, perhaps we should ask how sleep impacts exercise. The authors of this study were looking at exercise and sleep, especially in the elderly. We all sleep less as we get older, but chronic insomnia is a different beast entirely. When we don’t get enough sleep, we get snappish, have trouble concentrating, suffer from daytime sleepiness, and are more susceptible to things like getting sick, or getting in to accidents. © 2013 Scientific American
Link ID: 18533 - Posted: 08.20.2013
By Brady Dennis, Insomniacs of the world: If you think taking a long run today will make you sleep better tonight, think again. While exercise has long been a prescription for insomnia, new research suggests that exercise doesn’t immediately translate into a better night’s sleep — unless you stick with it for months. A study published Thursday in the Journal of Clinical Sleep Medicine found that aerobic exercise can lead to more rest at night for people who suffer from existing sleep problems, but only if they maintain an exercise regimen for roughly four months. “Exercise isn’t a quick fix. . . . It takes some time and effort,” the study’s lead author, Kelly Glazer Baron, a clinical psychologist and director of the behavioral sleep program at Northwestern University’s Feinberg School of Medicine, said in an interview. “It’s a long-term relationship.” Studies have long suggested that aerobic exercise can contribute to better sleeping habits. But much of the research on the daily effects of exercise on sleep was conducted with healthy sleepers. Tuesday’s study, by contrast, looked at the long-term effects of exercise in people already suffering from sleep disorders. © 1996-2013 The Washington Post
Link ID: 18526 - Posted: 08.19.2013
NICHOLAS SPITZER is a professor of neuroscience at the University of California. His research concentrates on the ways in which neurons take on specialised functions to enable signalling in the brain. He is editor-in-chief of BrainFacts.org, a public information service about the brain and nervous system, and is instrumental in the BRAIN Initiative, a research project backed by the White House to advance new technologies to help map the brain. What do you know about the brain that the rest of us don’t? The structure and function of the brain are determined by genes and environment. We think we know this—it’s nature and nurture—but what many don’t realise is that this remains true throughout life. People think the brain is malleable only when we’re young. But that’s just not true. The forms of plasticity we see in the young brain are sustained in the mature brain. By plasticity I mean the ability of the brain to change its structure and function in response to changes in the environment. In addition to the classical ways the brain changes (the strength of the connections, synapses and neurons) we now understand a third kind of brain plasticity in which the neurotransmitter molecules—the signals from one neuron to another—can actually switch. What does this mean for human development? Our experiments have mainly been done on adult rats. A finding that is directly related to the human condition is that putting the animals on different photoperiods [day and night cycles] changes the neurotransmitter identity in the hypothalamus [a part of the brain] and this changes the animal’s behaviour. When animals are on a short day (rats are nocturnal so a short day is good) they make dopamine, the reward chemical. On the long day the neurons switch from dopamine to somatostatin, which retards growth. © The Economist Newspaper Limited 2013.
Keyword: Biological Rhythms
Link ID: 18516 - Posted: 08.17.2013