18 Jul Sleep and your brain
Sleep and Your Brain
No one knows exactly why we need to sleep. But we certainly do. Some people are able to get by on less sleep than others. Randy Gardner, for instance, seems to be able to get by on very little. In 1964, as a teenager, he was able to stay awake for 11 days.
Although the brain can’t live on sleep alone, good sleep is an essential ingredient, necessary to keep your brain humming along. No one knows exactly why this is. However, new research is shedding some light on the matter.
Sleep allows the brain time for housekeeping functions.
The term ‘brainwashing’ usually has negative connotations: a naive individual being inducted in an evil cult. But it seems that your brain needs frequent washing, which is only accomplished when you fall asleep.
Sleep and Toxins
Just like in all tissues and organs of the body, toxins accumulate in your brain.
The brain demands a lot of fuel. Even though it’s mass accounts for only 2% of your body weight, it consumes 25% of your calories on a daily basis. All that metabolic activity produces waste products, which are washed away as you sleep.
This sleep related brain cleansing process was reported in experimental animals as early as 2013. At that time a laboratory technique was developed to directly measure the concentration of amyloid-β protein in the mouse brain. The scientists were investigating the response of the protein to stress. Accumulation of the protein in the brain correlates with the eventual formation of amyloid-β plaques in the brain and may contribute to Alzheimer’s disease. Unexpectedly, the neuroscientists discovered that the protein’s concentration peaked during waking hours and dropped precipitously as the rodents slept.
In 2019, a Boston based group of neuroscientists reported that brain washing also occurs in humans during sleep. The scientists recruited 13 volunteers, aged between 23 and 33, and studied the electrical signals and the fluid dynamics of their brains. The test subjects were fitted with special caps that measured the electrical activity of their brain (EEG). The testing took place at midnight so that the volunteers would fall asleep in an MRI scanner. The activity of the various fluids within the head were visualized during MRI.
The researchers determined that, as the volunteers entered a stage of sleep called non- REM (rapid eye movement), the electrical activity of their neurons (brain cells) started to synchronize, turning on and off at the same time. At those quiet moments, when the neurons had stopped firing, their requirement for oxygen decreased. As the demand for nutrients ebbed, the demand for blood flow into the brain (which would be required to bring those nutrients) proportionally fell.
The skull is an enclosed space. Therefore, when the volume of blood entering the brain tissue decreases something must fill the space.
The brain and spine are constantly bathed in and supported by a clear, colorless, watery fluid called cerebrospinal fluid (CSF). The neuroscientists observed, using MRI, that as the blood volume inside the substance of the brain ebbed, a tide of CSF washed over and through the brain. This CSF tide rhythmically receded as the electrical wave (EEG) of activity and blood flow increased.
The waves of CSF continued while the volunteers were in non-REM sleep and washed their brains, like a wave clearing the debris from a sandy shore. One scientist involved in the study, Dr. Lewis, noted that “We do see that the neural change always seems to happen first, and then it’s followed by a flow of blood out of the head, and then a wave of CSF into the head.”
She also noted that, “It’s now possible to tell if someone is sleeping or not, just by analysing the CSF patterns on a brain scan.”
Why can’t beneficial brain washing happen while you’re awake?
When you’re awake, neurons are not in the same synchronization as during non-REM sleep. The cells are not all turned on or off at the same time when you’re awake. In the awake brain, electricity and blood levels average out and remain relatively constant. There is no ebb and flow to cause substantial waves of cerebrospinal fluid to circulate around and through the brain and clear out all the metabolic byproducts that accumulate.
In the sleeping brain, CSF flows in to flush out debris, including toxins and proteins, like amyloid-β (known to accumulate in neurodegenerative diseases like Alzheimer’s). This knowledge could lead to new clinical applications for treating and preventing disease. Future interventions might focus on increasing the amount of cerebrospinal fluid that washes over the brain. That may help clear out amyloid-β but also could help with other toxins like tau, a protein that gets tangled in Alzheimer’s patients’ brains and disrupts the connections between neurons.
Substantial oscillations of fluid inflow to the brain appeared during sleep and were tightly coupled to functional magnetic resonance imaging signals and linked to electroencephalogram (EEG) slow waves. Slow oscillatory neuronal activity thus leads to oscillations in blood volume, drawing cerebrospinal fluid into and out of the brain. The sleeping brain exhibits waves of CSF flow on a macroscopic scale, and these CSF dynamics are interlinked with neural and hemodynamic rhythms.
The findings of a nightly brain washing may help gather insights into the many neurological and psychological disorders that are associated with disrupted sleep patterns. Sleep disorders may contribute to neurodegeneration: fragmented sleep may impede the clearance of neurotoxins and allow neuroinflammation and damage to cerebral vasculature. Learning to augment the nightly CSF rhythmic flow may cure or prevent disease and may even lead to an understanding on how to slow the aging process.
Sleep and synapses
Brain cells (neurons) communicate with each other and peripheral nerves across chasms called synapses. Synapses change throughout life as each neuron grows branches that reach towards other cells and those connections become refined in a pruning process. As neuronal timekeepers rhythmically force your internal clock to increase in ‘sleep pressure,’ the cells prepare to build proteins that maintain synapses. Researchers have discovered that, in the absence of sleep, neurons curtail their regular building of these critical proteins. Sara B. Noya at the University of Zurich and her colleagues reported that in mice, sleep triggers the final steps of protein production (the rhythmic generation of instructions, or transcripts).
These researchers discovered that maintaining a normal sleep cycle is crucial in protein production. Regulation occurred during two peak times in the 24-hour day, just before waking and sleeping. The pre-sleep time transcripts coded for proteins that regulate building other proteins, while the pre-wake time regulations were for proteins linked to synapse function. In sleep-deprived mice this protein making function is derailed, most severely for the synapse related proteins.
Franziska Brüning of the Ludwig Maximilian University of Munich and the Max Planck Institute of Biochemistry in Martinsried, Germany, and her colleagues further elucidated the effects of sleep on brain protein production. It is well known that adding or removing a molecule to a protein, called a phosphate group, can change the biological activity of that protein. The phosphate molecule acts as a toggle to turn proteins on or off. The scientists discovered that levels of proteins that had been tagged with phosphates peaked twice, with the bigger peak occurring just before waking.
Is too much sleep bad for your brain.
As you get older the classic eight hours a night sleep is more like a dream. Many studies have shown that poor quality sleep and extremes of sleep duration become common experiences for both middle-aged and older people. All of these sleep problems have been associated with increased risk of dementia and cognitive decline.
In 2017 a multinational group of researchers embarked upon the largest sleep study ever. The Worldwide sleep study has thus far involved tens of thousands of people. Scientists have reported that sleeping too little or too much has a negative impact on your cognitive ability. Volunteers underwent a battery of 12 well-established cognitive tests and reported their amount of sleep per night. The scientists recommended between seven and eight hours of sleep per night. Those who reported this amount of sleep had the highest level of mental ability. Those with fewer than six and a half or more than nine hours of sleep per night demonstrated lower performance on cognitive tests. Both more and less sleep negatively impacted a variety of cognitive functions, such as identifying complex patterns and manipulating information to solve problems. It was verbal ability that was most significantly impacted. It seems that when it comes to sleep, the Goldilocks rule is in place, not too little, not too much, just right.
Sleep and Frontal lobe
Part of your brain, the frontal lobe, remains on guard duty as you sleep. The main function of the frontal lobe is to control executive functions (decision making) and movement of the body.
A recent study in mice by Canadian scientists revealed that the frontal lobe monitors the environment while you sleep. Even in the deepest stages (Stage IV, described later) of sleep, the frontal lobe of the brain remains vigilant. It monitors the environment and wakes you up if it senses danger.
Sleep and Hippocampus
The hippocampus, part of the brain’s limbic system, is crucial in the process of consolidating short-term memory and forming long-term memory. The hippocampus is known to atrophy (waste away) during the normal aging process and more so in many pathologic neurodegenerative and neuropsychiatric conditions such as depression or dementia. Sleep related problems have been shown to accelerate and exacerbate hippocampal volume loss.
European scientists reported their findings in 3105 volunteers, who they followed for up to eleven years. The researchers compared sleep patterns to MRI-derived hippocampal volumes The researchers discovered worse sleep quality and daytime tiredness were related to greater hippocampal volume loss over time.
It is well known that sleep is important for memory consolidation (the process by which temporary memories are made permanent). Even short afternoon naps have been reported to have beneficial effects on memory performance. Scientists have reported significant drops in memory performance during sleep deprivation studies (during which an entire night of sleep is missed). The detrimental effects of insomnia on memory are especially severe for long-term rather than short-term memory. Scientists have recently elucidated the brain circuitry responsible for memory consolidation and the phase of sleep during which memories are consolidated.
Nucleus Reuniens and memory
Many students have noticed that if they studied hard for a test and then slept on it, they formed better, more permanent memories than if they spent all night cramming and then went to take the test. While the student slumbers, the nucleus reuniens plays a large role in turning knowledge into a more permanent memory.
The nucleus reuniens is a specific bundle of nerves in the center of the thalamus (the relay center of the brain). Using a combination of electrophysiological, optogenetic, and chemogenetic techniques in animal models, researchers have determined that the nucleus reuniens connects two other brain structures involved in creating memories: the prefrontal cortex (executive functions) and the hippocampus (memory functions). The nucleus reuniens may coordinate synchronous, rhythmically oscillating electrical activity between the prefrontal cortex and the hippocampus during a certain phase, slow-wave, sleep. This synching of far away brain regions may play an essential role in sleep-dependent memory consolidation.
Stage of sleep and memory
Scientists have described five stages of sleep, based on frequency of electroencephalogram (EEG) waves (electrical brain waves)
Stage I –
Stage I sleep may be noticed as a drowsy period. EEG waves slow down compared to being fully awake.
Stage II –
In stage II a light sleep is entered. EEG recordings reveal a further decrease in the frequency of electrical waves and an increase in their amplitude. Also seen are intermittent high-frequency spike clusters. These stage II clusters, known as sleep spindles arise as a result of interactions between the thalamus and cortex.
Stage III –
Stage III sleep is a moderate to deep sleep. EEG reveals a decrease in the number of sleep spindles decreases and the amplitude of low-frequency waves increases still more.
The deepest level of sleep is stage IV sleep. This may be called slow-wave sleep. It is most difficult to awaken people from slow-wave sleep. The EEG activity reveals low frequency, high-amplitude waves (called delta waves).
It is during stage IV sleep that EEG waves between the prefrontal cortex, the thalamus and the hippocampus become synchronized. It is this sge of sleep that scientists believe memory consolidation occurs. It is stage IV sleep where temporary memories become permanent.
Descending from drowsiness to deep stage IV sleep usually takes about an hour. Following a period of slow-wave sleep EEG recordings become similar to the awake state. REM (rapid eye movement) sleep is characterized by random eye movements, low muscle tone and vivid dreams. In a typical night’s sleep, people cycle through the different stages of sleep several times.
Sleep and Anxiety
A good night of slumber is essential for a stable psyche. A sleepless night, on the other hand, has been reported by scientists to increase anxiety levels by up to thirty percent. Many millions of people suffer from some form of anxiety and a non-pharmaceutical remedy is welcome news.
Researchers have discovered that stage IV sleep (the deepest stage) is when the psychological benefits are most powerful. During this non-rapid eye movement (NREM) slow-wave sleep, the electrical neural oscillation waves (EEG) become highly synchronized, and heart rates and blood pressure drop. Scientists believe that anxiety decreases, and stress is reduced, during stage IV sleep when the connections in the brain become reorganized.
In a series of recent experiments, a group of neuroscientists studied the brains of eighteen volunteers using an anxiety questionnaire, EEG (brain wave) testing and functional MRI. In a series of experiments, the young adults viewed emotionally stirring video clips after a full night of sleep, and again after a sleepless night. The researchers replicated the sleep-anxiety connection in a study of another thirty participants. Finally, they confirmed the results in an online: The scientists evaluated 280 people and tracked both their sleep habits and anxiety levels over four consecutive days.
The researchers reported that after a sleepless night, the activity of the medial prefrontal cortex, which normally helps keep our anxiety in check, was dramatically decreased. At the same time, the limbic system (emotional centers) and other deep structures went into overdrive. When the volunteers were allowed to enjoy a full night’s sleep (especially stage IV), their anxiety levels dropped and their stress levels improved.
One of the scientists, Dr. Walker concluded, “The best bridge between despair and hope is a good night of sleep.”