Sleep changes occur throughout life with infants sleeping the longest, up to 16 hours a day. 15% of this is spent in REM sleep. However, sleep is not continuous and they tend to wake up every hour due to their sleep cycles being shorter than adults and their need to feed regularly. Sleep stages are similar to adult SWS and REM but are immature versions known as quiet and active sleep. After 1 year REM decreases and brain activity begins to resemble that of an adult with total sleep time being around 13 hours a day with the entire sleep cycle taking 45-60 minutes. In childhood 30% of sleep in REM with about 12 hours per day spent sleeping.
There are several explanations as to why babies have this longer sleep period. One explanation is based on an evolutionary approach. This suggests babies sleep longer to allow parents to carry out daily duties therefore this sleep pattern is adaptive. However, as with any evolutionary explanation that are purely speculative and cannot be proven conclusively as they are post hoc.
The biological approach provides a different explanation explaining that babies sleeping patterns are due to their immaturity. Longer sleep patterns may be due to the vast amount of learning that is taking place. REM has been linked to production of neurotransmitters and consolidation of memory. As babies are born immature, they are expected to sleep more therefore this approach suggests sleep is important for mental health and development. Evidence for this comes from non-human animal studies such as dolphins. They are born mature and are able to swim and have almost no REM sleep. This supports that a biological approach can explain lifespan changes in sleep and why babies spend a vast amount of time sleeping. However, results from non-human animal studies lack external validity due to differences of anatomy between them and humans. The study can only suggest why such sleep behaviours occur, it cannot provide conclusive evidence to explain babies sleep patterns. However, such studies can help towards drawing conclusions. Without any studies this approach would be purely speculative.
Stickgold et al suggest may link to human development as we age. Evidence suggests REM may be linked to consolidation of procedural memory whereas SWS may be important for semantic and episodic. This may explain why REM is high in babies as they rapidly develop and also whit it decreases with age. This supports the assumption of lifespan changes occurring within sleep. Therefore provides validity to the theory of lifespan changes occurring. However, them memory consolidation process is difficult to measure. Therefore we are making the assumption that REM is linked to this based on correctional data which may decrease its reliability. However, it can be concluded changes in REM and SWS occur as we age with evidence of this coming from EEG recordings.
Another significant lifespan change in sleep occurs during old age. Adults typically sleep for 8 hours going through the sleep/wake cycle stages, with 25% of sleep spent in REM sleep and in old age sleep time remains roughly the same. Although REM sleep decreases to 20% of total sleep time and SWS is as low as 5% or non-existent in some, meaning less growth hormone is released for bodily repair. Age may bring a phase advance in circadian rhythm, feeling sleepier earlier and waking up earlier.
The reduction of sleep in old age may be due to health problems which affect sleep, not purely due to lifespan changes. Sleep disorders such as sleep apnoea interrupts sleep and may be used to explain why SWS is lower as sleep is more easily disturbed resulting in less growth hormone being produced, from less time spent asleep. Therefore research has ed to practical application of treatments being created e.g. melatonin supplements to aid sleep. Highlighting how research can be used in the real world to produce treatments to aid in better sleep.
No comments:
Post a Comment