Complex changes take place in the brain during sleep. It is far from a simple reduction in body process activity. Sleep provides balance in life, being part of a circadian rhythm.
Although its process is still not fully understood, the activity of the brain during sleep has been extensively scrutinised and gives an indication of what is happening.
Healthy sleep and circadian rhythms
Healthy sleep is considered to be the quantity and quality required to maintain optimal alertness during waking hours. The core time required is 2-5 hours.
Over the period of 24 hours, we are synchronised to sleep at night and be awake during the day. This sleep-wake balance is a prime example of a circadian rhythm, our internal time-keeping system. Circadian rhythms are biological cycles within the body that are regulated by hormones.
The hormone used in the sleep-wake cycle is melatonin which is secreted by the pineal gland in the brain, known as the third eye due to its ability to react to dark and light.
Melatonin levels are at their highest at night as darkness stimulates production in the body. Any exposure to light during the night reduces melatonin production by up to half.
REM and non-REM sleep
Most people will have heard of REM sleep, the Rapid Eye Movement stage, which can represent one quarter of total sleep time. This is the period when dreams become vivid. Non-REM sleep on the other hand is a deep progressive sleep.
We switch between REM and non-REM sleep involuntarily throughout the night. This cycle is more complicated than first appears, with changes in brain activity and body functioning.
Stages of sleep
The free falling interim between consciousness and sleep, as we lose sense of our surroundings, lasts about 5-15 minutes. This is the first of five stages. These go in cycles throughout the night, each lasting around 90 minutes.
Each stage is characterised by different brain wave patterns which may be measured by an electroencephalogram (EEG).
So what exactly is happening?
Non-REM sleep (stages 1-4):
The body's metabolism slows down; the brain is least active, blood pressure, heart rate and breathing are lower than during wakefulness. Hormones are secreted, including growth hormone which means that new proteins can go to work on renewal where required e.g. bone and skin. Some digestion takes place.
REM (stage 5):
The purpose of this stage is less certain. The brain is active, heartbeat and breathing are faster, and voluntary muscles are unable to move. There is a theory that psychological recuperation is occurring during REM sleep, the working out of emotional issues. Alternatively, the brain is sorting images of information that has been gathered throughout the day, filing some into long-term memory and discarding the rest.
| Stage 1 - the interim between consciousness and sleep (lasts about 5-15 mins)
Stage 2 - lose awareness of surroundings, heart rate slows, brain doing less complicated tasks (15 mins)
Stages 3/4 - body makes repairs needed, deep non-REM sleep (delta stage). Body temperature and blood pressure decrease
Stage 5 - REM - occurs about 90 mins after first feeling sleepy - increase in the contraction of eye muscles, eyes move, mind is active, and heart rate quickens. Breathing, blood pressure, and temperature all increase irregularly. It is during this stage that you wake, sometimes remembering a dream, though dreams are not restricted to this stage. |
The effect of ageing
Ageing alters our time-keeping organisation in the body as the number of pineal cells decreases, resulting in less melatonin production.
The proportion of delta sleep (stages 3 and 4) decreases with ageing, down to a tenth by the age of 50 compared to childhood, and in general we sleep for a shorter length of time at night.
Forms of insomnia
Insomnia is initiated by the inability to fall asleep, waking in the middle of the night or early in the morning. It is upsetting, frustrating, and can be debilitating.
If you suffer from insomnia you may be receiving adequate sleep, but you don't feel as though you are, which causes worry and further sleep loss.
To complicate matters further, some people dream that they are still awake, so there is a foreboding confusion as to whether you have slept at all. The key is to not worry. Get up and do something and just try to get whatever sleep you can at night.
The inability to fall asleep is frequently caused by stress. Sleep may improve as worry lessens. Short-term insomnia experienced by shift-workers and through jet lag occurs due to the internal time-keeping system becoming temporarily out of phase.
Suffering for more than three nights a week for at least a month is consistent with a diagnosis of chronic insomnia. This tends to be the result of an underlying medical condition such as depression, the experiencing of pain, respiratory problems, or alcohol abuse.
Some forms of prescription medication can also disrupt sleep patterns. You should discuss any concerns you have with your doctor.
Insomnia and health
Research has shown that when we are restricted to 4 hours sleep there are adverse effects on the ability to process nutrients and regulate hormones. In particular, glucose tolerance is affected. Total sleep deprivation can result in psychiatric breakdown.
Sleep loss can increase the severity of age-related chronic conditions and so contribute to an increased risk of mortality.
Tiredness causes accidents - with an estimated 15% considered to be due to fatigue. Road accidents in particular (e.g. falling asleep at the wheel) can be linked to the affects of sleep deprivation.
Insomnia can occur because of a number of reasons; many cases are a short term problem brought on by a stressful event, but there may be other underlying causes that need attention.
02/06/2009