Posts tagged deep sleep
Articles and news from the latest research reports.
Scientists probe the source of a pulsing signal in the sleeping brain
New findings clarify where and how the brain’s “slow waves” originate. These rhythmic signal pulses, which sweep through the brain during deep sleep at the rate of about one cycle per second, are assumed to play a role in processes such as consolidation of memory. For the first time, researchers have shown conclusively that slow waves start in the cerebral cortex, the part of the brain responsible for cognitive functions. They also found that such a wave can be set in motion by a tiny cluster of neurons.
"The brain is a rhythm machine, producing all kinds of rhythms all the time," says Prof. Arthur Konnerth of the Technische Universitaet Muenchen (TUM). "These are clocks that help to keep many parts of the brain on the same page." One such timekeeper produces the so-called slow waves of deep sleep, which are thought to be involved in transmuting fragments of a day’s experience and learning into lasting memory. They can be observed in very early stages of development, and they may be disrupted in diseases such as Alzheimer’s.
Previous studies, relying mainly on electrical measurements, have lacked the spatial resolution to map the initiation and propagation of slow waves precisely. But using light, Konnerth’s Munich-based team – in collaboration with researchers at Stanford and the University of Mainz – could both stimulate slow waves and observe them in unprecedented detail. One key result confirmed that the slow waves originate only in the cortex, ruling out other long-standing hypotheses. “The second major finding,” Konnerth says, “was that out of the billions of cells in the brain, it takes not more than a local cluster of fifty to one hundred neurons in a deep layer of the cortex, called layer 5, to make a wave that extends over the entire brain.”
New light on a fundamental neural mechanism
Despite considerable investigation of the brain’s slow waves, definitive answers about the underlying circuit mechanism have remained elusive. Where is the pacemaker for this rhythm? Where do the waves start, and where do they stop? This study – based on optical probing of intact brains of live mice under anesthesia – now provides the basis for a detailed, comprehensive view.
"We implemented an optogenetic approach combined with optical detection of neuronal activity to explore causal features of these slow oscillations, or Up-Down state transitions, that represent the dominating network rhythm in sleep," explains Prof. Albrecht Stroh of the Johannes Gutenberg University Mainz. Optogenetics is a novel technique that enabled the researchers to insert light-sensitive channels into specific kinds of neurons, to make them responsive to light stimulation. This allowed for selective and spatially defined stimulation of small numbers of cortical and thalamic neurons.
Access to the brain via optical fibers allowed for both microscopic recording and direct stimulation of neurons. Flashes of light near the mouse’s eyes were also used to stimulate neurons in the visual cortex. By recording the flux of calcium ions, a chemical signal that can serve as a more spatially precise readout of the electric activity, the researchers made the slow waves visible. They also correlated optical recordings with more conventional electrical measurements. As a result, it was possible to watch individual wave fronts spread – like ripples from a rock thrown into a quiet lake – first through the cortex and then through other brain structures.
A new picture begins to emerge: Not only is it possible for a tiny local cluster of neurons to initiate a slow wave that will spread far and wide, recruiting multiple regions of the brain into a single event – this appears to be typical. “In spontaneous conditions,” Konnerth says, “as it happens with you and me and everyone else every night in deep sleep, every part of the cortex can be an initiation site.” Furthermore, a surprisingly simple communication protocol can be seen in the slow wave rhythm. During each one-second cycle a single neuron cluster sends its signal and all others are silenced, as if they are taking turns bathing the brain in fragments of experience or learning, building blocks of memory. The researchers view these findings as a step toward a better understanding of learning and memory formation, a topic Konnerth’s group is investigating with funding from the European Research Council. They also are testing how the slow waves behave during disease.
The Connection Between Memory and Sleep
Researchers found information can be better retained with reinforcing stimuli delivered during sleep
When you’re studying for an exam, is there something you can do while you sleep to retain the information better?
"The question is, ‘What determines which information is going to be kept and which information is lost?’" says neuroscientist Ken Paller.
With support from the National Science Foundation (NSF), Paller and his team at Northwestern University are studying the connection between memory and sleep, and the possibilities of boosting memory storage while you snooze.
"We think many stages of sleep are important for memory. However, a lot of the evidence has shown that slow-wave sleep is particularly important for some types of memory," explains Paller.
Slow-wave sleep is often referred to as “deep sleep,” and consists of stages 3 and 4 of non-rapid-eye-movement sleep.
Paller’s lab group members demonstrated for Science Nation two of the tests they run on study participants. In the first experiment, the subjects learned two pieces of music in a format similar to the game Guitar Hero. During a short nap following learning, just one of the learned tunes was played softly several times, to selectively reinforce the memory for playing that tune without any reinforcement but not for the other tune. Paller wanted to know whether the test subjects could more accurately produce the tune played during sleep.
In the second exercise, the subjects were asked to memorize the location of 50 objects on a computer screen. The presentation of each object was coupled with a unique sound. During the post-learning nap, memory for the location of 25 objects was reinforced by the play-back of only 25 of the sounds. In this case, Paller wanted to know whether the subjects could remember object locations better if the associated sounds were played during sleep.
Researchers recorded electrical activity generated in the brain using EEG electrodes attached to the scalp. They thus determined whether the subjects entered “deep sleep,” and only those who did participated in the reinforcement experiments. In both experiments, participants did a better job remembering what was reinforced while they slept, compared to what was not reinforced.
"We think that memory processing happens during sleep every night," says Paller. "We’re at the beginning of finding out what types of memory can be reinforced, how large reinforcement effects can be, and what sorts of stimuli can be used to reactivate memories so that they can be better consolidated."
Paller’s goal is to better understand the fundamental brain mechanisms responsible for memory. And that, in turn, may help people with memory problems, including those who find themselves more forgetful as they age.
"We experience progressively less slow-wave sleep as we age. Of course, many brain mechanisms come into play to allow us to remember, including some processing that transpires during sleep. So, there’s a lot to figure out about how memory works, but I think it’s fair to say that the person you are when you’re awake is partly a function of what your brain does when you’re asleep," explains Paller. He says these reactivation techniques could turn out to be valuable for enhancing what people have learned.
"What is beautiful about this set of experiments is that Dr. Paller identified ‘deep sleep’ as a critical time window during which memory for specific experiences can be selectively enhanced by the method of reactivation without conscious effort," says Akaysha Tang, director of the cognitive neuroscience program in the NSF Directorate for Social, Behavioral and Economic Sciences.
"Normally, conscious rehearsal of memorized material is needed if one wants to remember something better or retain it for longer, and one has to find time to review or rehearse," continues Tang. "Dr. Paller and the members of his lab group showed that such selective enhancement could be achieved without conscious effort and without demanding more of one’s waking hours. So, instead of pulling that all-nighter to memorize the material, in the future, it may be possible to consolidate the memory by sleeping with a scientifically programmed lullaby!"
(Source: nsf.gov)
Slow-wave sleep, or ‘deep sleep’, is intimately involved in the complex control of the onset of puberty, according to a recent study accepted for publication in The Endocrine Society’s Journal of Clinical Endocrinology and Metabolism (JCEM).
The many changes that occur in boys and girls during puberty are triggered by changes in the brain. Previous studies have shown that the parts of the brain that control puberty first become active during sleep, but the present study shows that it is deep sleep, rather than sleep in general, that is associated with this activity.
"If the parts of the brain that activate the reproductive system depend on deep sleep, then we need to be concerned that inadequate or disturbed sleep in children and young adolescents may interfere with normal pubertal maturation," said Harvard researcher, Natalie Shaw, MD, of Massachusetts General Hospital and Boston Children’s Hospital who led the study. "This is particularly true for children who have been diagnosed with sleep disorders, but may also have more widespread implications as recent studies have found that most adolescents get less sleep than they require."
In the study, researchers examined pulses of luteinizing hormone (LH) secretion in relation to specific sleep stages in children ages 9-15. LH is essential for reproduction and triggers ovulation in females and stimulates the production of testosterone in males. Researchers found that the majority of LH pulses that occur after sleep are preceded by deep sleep suggesting that deep sleep is intimately involved in pubertal onset.
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