ARJUN’s SCIENCE UPDATE

Arjun D, Year 12 writes...

Our superpower: REM Sleep

The REM (rapid eye movement) phase of sleep consolidates our memories, processes that we have learned, and even improves our mood every single day, making it the most important phase of sleep for mental performance and health.

What is REM sleep and what happens?

The REM phase of sleep is only about 25% of our sleep and the electroencephalogram - EEG (recording of brain activity when a machine picks up electrical signals made by the brain) detects beta waves, similar to when we are awake, during REM phase of sleep. Beta waves have a high frequency (number of waves passing a particular point each second) and a low amplitude (maximum height of wave measured from starting height of wave - its equilibriumie size of wave).

Being in the REM phase of sleep is similar to being awake because of beta waves detected. However, there are a few changes:

• Our skeletal muscles can not move because otherwise we would act out our dreams

• Our breathing muscles are active and breathing is irregular

• Blood pressure and heart rate (number of heartbeats per second) increases

• Our eyes move rapidly about 15.9 times per minute, though we do not blink

When and how often are we in REM sleep?

The REM phase of our sleep starts about 90 minutes after we fall asleep and, every 90 minutes, our REM sleep phase gets longer. So, when we first achieve REM sleep it is only for roughly 10 minutes. However, our last REM sleep cycle, before we wake up, could last for about an hour.

During REM sleep, we dream and have nightmares because chemical processes in our brain (metabolism) go up by 20% so, usually, when people wake up in the middle of the night, it is because of and during REM sleep.

What is sleep?

There are two types of sleep: rapid eye movement (REM) and nonrapid eye movement (NREM), divided into five stages.

Stage 1: Wake Alert (During the day or just got into bed)

Electroencephalogram (EEG) recording: beta waves detected which have a high frequency and low amplitude. However, alpha waves are also detected when tired. When eyes are open, mainly beta waves detected. However when eyes are closed, mainly alpha waves are detected by EEG.

Stage 2: N1 (Light sleep, 5% of sleep) EEG recording: theta waves made by brain which have a low voltage. So, brain activity is low as nerve cell messages are transmitted by electrical current.

This starts when more than 50% of the alpha waves are replaced with low-amplitude mixed-frequency waves. The skeletal muscles can move and breathing is regular. This sleep stage in the cycle lasts for about 1-5 minutes, every 90 to 110 minutes - accounting for roughly 5% of total sleep time.

Stage 3: N2

(Deeper sleep, 45%)

The majority of sleep is N2 phase, which lasts about 25 minutes every 90 to 110 minutes and, like the REM phase, increases with each cycle. During this stage, heart beat and body temperature drops.

EEG recording: machine detects sleep spindles, which are brief and powerful bursts of neuronal (nerve cell) firing in the parts of the brain listed below:

• Superior temporal gyriresponsible for processing sounds including language.

• Anterior cingulate - regulates behavior and controls learning.

• Insular cortices - controls the sense taste, risk-reward behaviour, ie judgment and functioning of inner-ear including hearing etc.

• Thalamus - processes sensory signals, eg hearing, smell etc.

Furthermore, studies suggest sleep spindles contribute to memory consolidation.

K-complexes (delta waves) lasting roughly 1 second are shown to maintain sleep and memory consolidation unlike beta waves which makes us more alert.

Stage 4: N3

(N3, Stage 3 - Deepest sleep, 25%, and important for physical health) EEG recording: machine detects delta waves - lowest frequency, highest amplitude deepest stage of sleep. This sleep stage is the most difficult to awaken from, even if a sound higher than 100 decibels is played. This is because this phase repairs and regrows tissues, builds bone and muscle, and strengthens our immune system, so we feel refreshed the next day.

Stage 5: REM (Important phase for human mental performance) Although growth and repair of body mainly happens in non-

REM sleep, REM sleep is known to make us better learners by consolidating nerve cell pathways within us, thus reinforcing the things we learned during the day. REM is also like therapy, as we process emotions throughout the day, leaving us fresh for tomorrow. So, REM sleep improves mental health, which is just as important as physical health!

Can we increase the amount of REM sleep we get each night?

The simple answer is no. However all it takes are good sleep habits (for example: sleeping in a dark, quiet and cool room, sticking to a regular wake up time) which can increase the amount of sleep we get which, in turn, increases amount of REM sleep we get.

Mystery awaiting discovery? Is there a link between REM sleep and life expectancy?

We know sleep brings many benefits! So, lets go get that REM!