Sleep V
The meaty stuff starts now! Im in that phase of life where most of my friends are having kids. As I was reading through this part of the book on how sleep assists infants and adolescent, my enthusiasm to share bits and pieces of what i was learning with them must have been quite irritating to them. But considering how immensely important the information was i could not stop myself. Most folks who have babies are cognisant about the need for sleep and frankly babies don't do anything but sleep in the first few months anyway. It is the folks who have pre-adolescent kids and adolescents who need to be told about the importance of sleep and the way it changes as the kids mature from one stage of life to another. I knew there was something draconian about super early school-start times, this book has scientific data to back my previously baseless theory! Additionally Matthew also informs us about how sleep then disintegrates towards the later stages of our lives, both in quality and quantity. I will try to keep it succinct.
Sleep and Pregnancy
By the end of the second trimester, the majority of neural network needed to produce NREM and REM sleep have been established. The one thing that has not been put in place is the muscle-inhibiting system during REM sleep - hence the kicks a mother feels is the baby actually in deep REM sleep that is categorised by intense brain activity! It is only when the fetus enters the third trimester that real wakefulness emerges. However, as total sleep time decreases, the time spent in REM sleep increases, with the last two-weeks of pregnancy seeing up to 9 hours of REM sleep and the last week seeing 12 hours of REM sleep - the most a human being will feast on in their lifetime!
This happens mainly because REM sleep is important for brain maturation - intricate creation of the brain and its parts happen during the 2nd and 3rd trimesters when REM-sleep is dominant. This sleep, Matthew says, acts as a "electrical fertilizer" helping develop neural pathways and furnishing each healthy connecting ends known as synaptic terminal. This phase of development which infuses the brain with many neural connections is called synaptogenesis, because it involves the creation of millions of wiring links (synapses) between neurons. REM sleep hence helps with the setting up the neural architecture of the brain, a herculean task of construction. Depriving the developing infant of this REM sleep stalls the construction of the neural networks and the cerebral cortex of the brain. And this is irreversible, the brain remains in an under-developed state.
Autism Spectrum Disorder & Sleep
Deficient REM sleep has been found connected with ASD - autism spectrum disorder, a neurological condition characterised by a lack of special interaction. Imbalances in synaptic connections are common in autistic individuals. Autistic children do not have sound sleeping schedules and have a weaker circadian rhythm, with a flatter melatonin release across the 24hr period rather than a powerful rise in concentration at night and a rapid fall throughout the day. Hence the signal for when to sleep and when to wake is very weak, as compared to non-autistic children.
Matthew however asks the question I wondered after I read through the above findings about REM sleep and ASD - what is the direction of causality? We don't know. However, he does mention that in a (very sad) experiment when an infant rat was deprived of REM sleep, they became isolated and withdrawn.
Alcohol and Pregnancy
Alcohol taken during pregnancy crosses the placental barrier and reaches the fetus. New borns of mothers who were heavy drinkers during pregnancy registered a much lower time spent in REM sleep as compared to infants of the same age of mothers who didn't drink. Most women do not drink heavily during pregnancy, but some do allow themselves a drink or two. What are the effects of that occasional glass of wine on the fetus? It still affects the REM sleep of the fetus as well as a depression in breathing during REM sleep. How about alcohol during breast feeding? Alcohol is readily absorbed in breast milk, babies consuming this milk will spend more time awake and 20-30% suppression of REM sleep soon after - they will try to get back that REM sleep once the alcohol is cleared from their system, but it is not easy for those tiny tender systems to do so.
"REM sleep is not optional during early human life, but obligatory. Every hour of REM sleep appears to count, as evidenced by the desperate attempt by a fetus of newborn to regain any lost REM sleep.............blocking or reducing REM sleep in a newborn animal hinders and distorts brain development, leading to an adult that is socially abnormal."
Childhood sleep
As compared to a monopshaic sleep of adults in industrialized nations, infants and children display polyphasic sleep - many short naps through the day and night. As the child grows older, their sleep gets more stable, with fewer and longer bouts. This is mainly because the circadian rhythm isn't set yet. The suprachiasmatic nucleus that governs the rhythm is still under development as the child is growing - only post 3-4 months will the newborn show signs of a stable rhythm.
I have friends who both gave birth this year and they are at this very moment in time trying to set a clear rhythm for their babies in terms of temperature, feed timings, bath timings- all repeating signals - so that their suprachiasmatic nucleus gets assistance to set up a strong 24-hour rhythm. In one year, this part of the child's brain is well developed and hence they aren't waking up every few hours and are instead spending long hours in nighttime sleep.
Matthew however shares some interesting data about the share of NREM and REM sleep as the total sleep time decreases with age. When the infant is 6 months old, the split is 50/50, when they are 5 years old they have a 70-30 NREM-REM split! The proportion of REM sleep time decresaes in early childhood, as total sleep time decreases. This will finally stabilize to a 80-20 split of NREM-REM in teen years and stay that way through early and mid adulthood.
Sleep and Adolescence
REM sleep plays a vital role in setting up the networks of the brain in early developmental years of human life, it is also responsible to "activate those pathways with a healthy dose of informational bandwidth".
After this first round, sleep tries to fine tune the wiring a little bit - in fact to scale it back down to make it more efficient and effective. I find this part very interesting. The REM sleep help lay the groundwork for anything that the human being might use in their lives- language learning, musical skills and many other demands that we exercise on the brain. Now all this wiring exists, due to the diligent work of REM sleep, but the further development of specific parts of that infrastructure depends on the usage and experiences the child is introduced to in their early lives. This is where what Matthew calls "individual refinement" comes in. "A somewhat generic brain becomes ever more individualized based on the personalised use of the owner". This is where NREM sleep plays a major role. It plays the role of "synaptic pruning that features prominently during adolescence"
A theory sleep researcher Irwin Feinberg proposed was as deep NREM sleep performs its final overhaul and refinement of the brain during adolescence, cognitive skills, reasoning and critical thinking start to improve. The changes in deep NREM sleep always precede the cognitive and developmental milestones within the brain by several week or months, implying a direction of influence.
A second discovery by Feinberg was that brain maturation moved from the back of the brain governing the visual and spatial perception to the frontal lobe that managed rational thinking and critical decision-making.
Understanding the patterns of development has helped with the understanding of many psychiatric disorders that show up in early childhood and adolescence. For eg, those individuals who developed schizophrenia had an abnormal pattern of brain maturation that was associated with synaptic pruning, especially in the frontal lobe regions where rational thoughts are controlled - the inability to do so being a major symptom of schizophrenia.
And the last point on sleep during adolescence is on different circadian rhythms. During puberty the timing of the suprachiasmatic nucleus is shifted forward. A 16 year old will not feel sleepy at 9 pm - the rising tide of melatonin is many hours away and at 9 pm peak wakefullness is still at play - this is a biological fact not something that they can control. Mother nature does this so that the adolescents who in this critical time are learning to be independent get a few more hours of the night away from parental influence so that they can interact with other teenagers and build a social peer group. How cool is that!
Sleep in Midlife and Old Age
All this talk about sleep being important in earlier stages of our life would make one think that as we grow older sleep is not really that important. But the truth is far from it. Many surveys worldwide have reported people needing and trying to get more sleep!
Matthew walker names three main challenges that afflict older adults with respect to sleep:
Since reading this book, many a time, my first reaction to a health scare a friend or relative has is "are you sleeping enough" and I get stared at as though I was mad, with a "what does sleep have to do with it" face even. Such is our ignorance about all that sleep does for us.
Sleep and Pregnancy
By the end of the second trimester, the majority of neural network needed to produce NREM and REM sleep have been established. The one thing that has not been put in place is the muscle-inhibiting system during REM sleep - hence the kicks a mother feels is the baby actually in deep REM sleep that is categorised by intense brain activity! It is only when the fetus enters the third trimester that real wakefulness emerges. However, as total sleep time decreases, the time spent in REM sleep increases, with the last two-weeks of pregnancy seeing up to 9 hours of REM sleep and the last week seeing 12 hours of REM sleep - the most a human being will feast on in their lifetime!
This happens mainly because REM sleep is important for brain maturation - intricate creation of the brain and its parts happen during the 2nd and 3rd trimesters when REM-sleep is dominant. This sleep, Matthew says, acts as a "electrical fertilizer" helping develop neural pathways and furnishing each healthy connecting ends known as synaptic terminal. This phase of development which infuses the brain with many neural connections is called synaptogenesis, because it involves the creation of millions of wiring links (synapses) between neurons. REM sleep hence helps with the setting up the neural architecture of the brain, a herculean task of construction. Depriving the developing infant of this REM sleep stalls the construction of the neural networks and the cerebral cortex of the brain. And this is irreversible, the brain remains in an under-developed state.
Autism Spectrum Disorder & Sleep
Deficient REM sleep has been found connected with ASD - autism spectrum disorder, a neurological condition characterised by a lack of special interaction. Imbalances in synaptic connections are common in autistic individuals. Autistic children do not have sound sleeping schedules and have a weaker circadian rhythm, with a flatter melatonin release across the 24hr period rather than a powerful rise in concentration at night and a rapid fall throughout the day. Hence the signal for when to sleep and when to wake is very weak, as compared to non-autistic children.
Matthew however asks the question I wondered after I read through the above findings about REM sleep and ASD - what is the direction of causality? We don't know. However, he does mention that in a (very sad) experiment when an infant rat was deprived of REM sleep, they became isolated and withdrawn.
Alcohol and Pregnancy
Alcohol taken during pregnancy crosses the placental barrier and reaches the fetus. New borns of mothers who were heavy drinkers during pregnancy registered a much lower time spent in REM sleep as compared to infants of the same age of mothers who didn't drink. Most women do not drink heavily during pregnancy, but some do allow themselves a drink or two. What are the effects of that occasional glass of wine on the fetus? It still affects the REM sleep of the fetus as well as a depression in breathing during REM sleep. How about alcohol during breast feeding? Alcohol is readily absorbed in breast milk, babies consuming this milk will spend more time awake and 20-30% suppression of REM sleep soon after - they will try to get back that REM sleep once the alcohol is cleared from their system, but it is not easy for those tiny tender systems to do so.
"REM sleep is not optional during early human life, but obligatory. Every hour of REM sleep appears to count, as evidenced by the desperate attempt by a fetus of newborn to regain any lost REM sleep.............blocking or reducing REM sleep in a newborn animal hinders and distorts brain development, leading to an adult that is socially abnormal."
Childhood sleep
As compared to a monopshaic sleep of adults in industrialized nations, infants and children display polyphasic sleep - many short naps through the day and night. As the child grows older, their sleep gets more stable, with fewer and longer bouts. This is mainly because the circadian rhythm isn't set yet. The suprachiasmatic nucleus that governs the rhythm is still under development as the child is growing - only post 3-4 months will the newborn show signs of a stable rhythm.
I have friends who both gave birth this year and they are at this very moment in time trying to set a clear rhythm for their babies in terms of temperature, feed timings, bath timings- all repeating signals - so that their suprachiasmatic nucleus gets assistance to set up a strong 24-hour rhythm. In one year, this part of the child's brain is well developed and hence they aren't waking up every few hours and are instead spending long hours in nighttime sleep.
Matthew however shares some interesting data about the share of NREM and REM sleep as the total sleep time decreases with age. When the infant is 6 months old, the split is 50/50, when they are 5 years old they have a 70-30 NREM-REM split! The proportion of REM sleep time decresaes in early childhood, as total sleep time decreases. This will finally stabilize to a 80-20 split of NREM-REM in teen years and stay that way through early and mid adulthood.
Sleep and Adolescence
REM sleep plays a vital role in setting up the networks of the brain in early developmental years of human life, it is also responsible to "activate those pathways with a healthy dose of informational bandwidth".
After this first round, sleep tries to fine tune the wiring a little bit - in fact to scale it back down to make it more efficient and effective. I find this part very interesting. The REM sleep help lay the groundwork for anything that the human being might use in their lives- language learning, musical skills and many other demands that we exercise on the brain. Now all this wiring exists, due to the diligent work of REM sleep, but the further development of specific parts of that infrastructure depends on the usage and experiences the child is introduced to in their early lives. This is where what Matthew calls "individual refinement" comes in. "A somewhat generic brain becomes ever more individualized based on the personalised use of the owner". This is where NREM sleep plays a major role. It plays the role of "synaptic pruning that features prominently during adolescence"
A theory sleep researcher Irwin Feinberg proposed was as deep NREM sleep performs its final overhaul and refinement of the brain during adolescence, cognitive skills, reasoning and critical thinking start to improve. The changes in deep NREM sleep always precede the cognitive and developmental milestones within the brain by several week or months, implying a direction of influence.
A second discovery by Feinberg was that brain maturation moved from the back of the brain governing the visual and spatial perception to the frontal lobe that managed rational thinking and critical decision-making.
Understanding the patterns of development has helped with the understanding of many psychiatric disorders that show up in early childhood and adolescence. For eg, those individuals who developed schizophrenia had an abnormal pattern of brain maturation that was associated with synaptic pruning, especially in the frontal lobe regions where rational thoughts are controlled - the inability to do so being a major symptom of schizophrenia.
And the last point on sleep during adolescence is on different circadian rhythms. During puberty the timing of the suprachiasmatic nucleus is shifted forward. A 16 year old will not feel sleepy at 9 pm - the rising tide of melatonin is many hours away and at 9 pm peak wakefullness is still at play - this is a biological fact not something that they can control. Mother nature does this so that the adolescents who in this critical time are learning to be independent get a few more hours of the night away from parental influence so that they can interact with other teenagers and build a social peer group. How cool is that!
Sleep in Midlife and Old Age
All this talk about sleep being important in earlier stages of our life would make one think that as we grow older sleep is not really that important. But the truth is far from it. Many surveys worldwide have reported people needing and trying to get more sleep!
Matthew walker names three main challenges that afflict older adults with respect to sleep:
- Reduced quality/quantity
Since reading this book, many a time, my first reaction to a health scare a friend or relative has is "are you sleeping enough" and I get stared at as though I was mad, with a "what does sleep have to do with it" face even. Such is our ignorance about all that sleep does for us.
- Reduced sleep efficiency
The last point on old age and fragmented sleep is that the elderly are more prone to falls and fractures as a result of those due to waking up in the night and often being groggy while trying to navigate our way through the dark.
Many people used to believe that older people need less sleep. But Matthew and his team have shown through many experiments that they still need that sleep, they are unable to generate it. When they are artificially assisted in obtaining that sleep - they benefit from it, which would not be true had their sleep need been fulfilled.
- Disrupted timing of sleep
This has to do with the circadian timing. As opposed to adolescents, the elderly face a regression in sleep timing leading to earlier and earlier bedtimes associated with an early peak in melatonin release. Often times we see older adults snoozing early evening which then further disrupts sleep at nighttime because it interferes with sleep pressure, clearing away the adenosine that was building up throughout the day. Additionally, Matthew states, as we get older, the circadian rhythm grows weaker as does the amount of melatonin released in the brain.
Matthew offers very implementable solutions though!
- Exposure to light in the evenings: Artificial evening light often hampers with the circadian rhythm of adults fooling the brain into believing it isn't night yet and delaying the release of melatonin. While this is not good for young adults, for the older adults we can use this to our benefit. To deal with a regressive circadian rhythm we can expose them to bright light in the late afternoon hours.
- Wearing sunglasses during morning exercise outdoors - fooling the rhythm again that is set to a early-to-rise schedule.
- Prescription melatonin has been found to help with the circadian rhythm, reducing the time taken to fall asleep and improving self reported sleep quality and morning alertness.
What is the cause of this decline in sleep quality, efficiency and timing? Matthew along with a few researches conducted a study that found that the brain undergoes degeneration as we age, specifically they discovered the following :
- The areas of the brain that suffers the most are the same deep-sleeping generating regions - middle-frontal regions seated above the bridge of the nose.
- Older adults suffered a 70% loss of deep sleep as compared to young adults
- The above two are connected - the more significant the deterioration of the mid-frontal region of their brain, the more deep NREM sleep they lost.
In further tests they did to test memory and forgetfulness, they discovered that older adults showed more overnight forgetting - poor memory and poor sleep are hence interrelated.
Many people used to believe that older people need less sleep. But Matthew and his team have shown through many experiments that they still need that sleep, they are unable to generate it. When they are artificially assisted in obtaining that sleep - they benefit from it, which would not be true had their sleep need been fulfilled.
"Poor sleep is one of the most under appreciated factors contributing to cognitive and medical ill health in the elderly, including issues of diabetes, depression, chronic pain, stroke, cardiovascular disease and Alzheimer's disease."
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