Before I Go To Sleep (2014)
Marybelle Bailey
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Study objectives: Obstructive sleep apnea (OSA) is commonly associated with cognitive and functional deficits, some of which are resolved after continuous positive airway pressure (CPAP) treatment. The investigation of brain structural changes before and after treatment could provide deep insights into the pathogenesis and the reversibility of this disorder. We hypothesized that severe OSA patients would have altered white matter (WM) integrity and cognition and that treatment would improve both the structural damage and the cognitive impairment.
Results: Results in pre-treatment OSA patients showed impairments in most cognitive areas, mood and sleepiness that were associated with diffuse reduction of WM fiber integrity reflected by diminished fractional anisotropy (FA) and mean diffusivity (MD) in multiple brain areas. After 3 months of CPAP, only limited changes of WM were found. However, over the course of 12 months CPAP treatment, an almost complete reversal of WM abnormalities in all the affected regions was observed in patients who were compliant with treatment. Significant improvements involving memory, attention, and executive-functioning paralleled WM changes after treatment.
Conclusions: Changes of WM DTI "signatures" of brain pathology in OSA patients are appreciable over the course of 12-month treatment with CPAP in most of the regions involved. Recovery of cognitive deficits after treatment is consistent with the presence of a reversible structural neural injury in OSA in patients who were compliant with treatment.
This study investigated whether the use of a television, computer, gaming console, tablet, mobile phone, or audio player in bed before going to sleep was associated with insomnia, daytime sleepiness, morningness, or chronotype. 532 students aged 18-39 were recruited from lectures or via e-mail. Respondents reported the frequency and average duration of their in-bed media use, as well as insomnia symptoms, daytime sleepiness, morningness-eveningness preference and bedtime/rise time on days off. Mean time of media use per night was 46.6 minutes. The results showed that computer usage for playing/surfing/reading was positively associated with insomnia, and negatively associated with morningness. Mobile phone usage for playing/surfing/texting was positively associated with insomnia and chronotype, and negatively associated with morningness. None of the other media devices were related to either of these variables, and no type of media use was related to daytime sleepiness.
Jilly set up a Facebook page and a Twitter account to encourage her fellow students to show up at the school board meeting where the vote was taking place. With their help, she made hundreds of posters and flyers. Then, armed with a mountain of scientific research she and her friends had collected, she stood before the board and made the case against an earlier start time. It worked.
The school board abandoned the idea of beginning the day at 7:20 a.m. Jilly was not through, though. The next day, she started campaigning for an even later start time, and her persistence paid off. Eventually, the board voted 6 to 1 to ring the first bell more than an hour later, at 9 a.m.
These brain signals explain how our bodies know when to produce melatonin, but how is melatonin synthesized? Melatonin is actually derived from an amino acid called tryptophan, which is absorbed from the bloodstream to the pineal gland. An amino acid is an organic acid used to make proteins.
The synthesis of melatonin from tryptophan occurs through a multistep process (Fig. 2). First, tryptophan is converted to another amino acid, 5-hydroxytryptophan, through the action of the enzyme tryptophan hydroxylase and then to a brain chemical called serotonin by an enzyme called aromatic amino acid decarboxylase. An enzyme is a biological catalyst that speeds up the rate of a chemical reaction.
Serotonin's conversion to melatonin involves two enzymes: serotonin-N-acetyltransferase (SNAT), which converts the serotonin to N-acetylserotonin with the addition of an acetyl group (COCH3), and hydroxyindole-O-methyltransferase (HIOMT), which transfers a methyl group (CH3) to the N-acetylserotonin. The activities of both enzymes rise soon after the onset of darkness.
As we have learned more about the chemistry of sleep in the past few decades, we have come to realize that it really is harder for teens, such as Jilly, to wake up early. In teens, melatonin is produced about three hours later in the 24-hour sleep cycle than in children or adults. This keeps them up late, and when they wake up early, SNAT is still active and they are still producing melatonin, which leaves them feeling sleepy in the morning.
Even more surprising is the number of car crashes involving teenagers in Fayette County, Kentucky, decreased by almost 17% in the two years following its adoption of a later start time for school. So, it appears that taking into consideration a shift in the timing of melatonin production in teens can have all sorts of benefits.
Also, some high school students involved in after-school activities dislike having to stay at school until dark. Clearly, balancing the biological sleep schedule of teenagers with the demands of society is difficult, but more and more districts are interested in trying to make later start times work.
Melatonin is not the only chemical that determines our sleep schedule. Adenosine also plays an important role: it slows down the activity of neurons. It gradually builds up in our bodies when we are awake and makes us feel sleepy by the end of the day. Then, when we sleep, adenosine molecules break down, so the cycle can start all over again. Our neurons, or nerve cells, are embedded with adenosine receptors. When adenosine binds to these receptors, a variety of proteins that inhibit neurons are released. This suppression of nerve cell activity is what causes the feeling of drowsiness.
Caffeine has a chemical structure similar to that of adenosine (Fig. 1). Both molecules have a double-ring structure, which allows caffeine to bind to adenosine receptors. Unlike adenosine, however, caffeine does not activate these receptors or suppress neuron activity. By reducing the concentration of available adenosine receptors, caffeine slows the rate of reaction: Less-bound adenosine means we feel less sleepy.
A little caffeine can be a good thing. It can temporarily improve memory, decrease fatigue, and improve mental functioning. But too much caffeine can cause negative side effects, such as insomnia, tremors, nausea, chest pain, and heart palpitations. In fact, over a three-year period, the Illinois Poison Center in Chicago counted more than 250 cases of medical complications that involved caffeine, 12% of which ended in hospitalization. The average age of the patients was 21, suggesting that young people are particularly prone to overindulging in caffeine. So be careful not to overdo it!
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Once we fall asleep, there are multiple stages within sleep itself. We start off awake, and then as we drift off we enter stage 1 sleep. Here, the muscles are active, and the eyes open and close moderately. This stage lasts between two and five minutes before we enter stage 2 sleep. Our heart rate and body temperature both drop in this stage and full muscular relaxation occurs (including our throat, which is what causes snoring). Moving into a deeper sleep, we enter stages 3 and 4, which is where slow wave sleep (SWS) occurs. Here, we have very slow brain waves, and we are incredibly hard to wake up. This stage of sleep is vital to health; the hormones that enable us to grow and repair are released during this stage, and it is generally a highly anabolic environment. Important information from the day is also consolidated into memory during SWS.
After about 30 minutes of SWS, we quickly shift back to stage 2 sleep and then into REM sleep. REM stands for rapid eye movement, and it is in this stage that dreams occur. Our muscles are paralyzed (to stop us acting out our dreams), but our brain is highly active. REM sleep plays a large role in the creation of memories and problem solving. After a period of REM sleep, we will then have a brief micro awakening, of which we will have no memory of when we wake up for real. We then move back into stage 2, then into SWS. This cycle is repeated over the night; deep sleep tends to occur in a greater proportion earlier in the night, and REM sleep occurs in a greater proportion later in the night. In a typical night, 50 percent of the time is spent in a light sleep, 20 per cent in a deep sleep, 25 percent in REM, and 5 per cent awake. Each sleep cycle takes roughly 90 minutes.
The general recommendations are that adults should aim to sleep for between 7 and 9 hours per night. The lack of sleep is associated with a wide range of health and performance issues. From a health point of view, sleep deprivation is associated with an increased risk of all cause mortality. Lack of sleep can more than double the risk of death from cardiovascular disease. Short sleep is a risk factor for weight gain (it causes an increase is ghrelin, the hunger hormone, and a decrease in leptin, the hormone that makes you feel full), hypertension, and type II diabetes (sleep deficiency reduces insulin sensitivity). Disrupted circadian rhythms are also bad for your health; shift work is categorized as a carcinogen by the World Health Organisation. The mechanism for this is that melatonin, which causes you to feel sleepy, limits the production of hormones that associated with causing cancer.
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