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We all sleep and for most people this is inactivity for 6 – 8 hours each day.  About one third of our lives are spent sleeping.  It is a period of rest and recovery for the body and brain, but it is unclear why humans, along with all other animals, need to sleep.  It would be a distinct evolutionary advantage for an animal if it did not require sleep – but there do not appear to be any exceptions.  Sleep is a universal requirement for life on this planet.

We sleep in 90 minute cycles, and we generally have 4 – 6 of these each night if we do not get disturbed.  There is debate over exactly how much sleep we require, but 5 x 90 minutes = 7.5 hours is a good benchmark.  Contrary to the way life works in the western world, there is evidence to suggest that we prefer to sleep twice per day, perhaps similar to life in Mediterranean other other hot countries where people tend to have a siesta for a few hours in the middle of the day and then retire again late in the evening.

Falling asleep is a gradual process.  There isn’t an on/off switch.  For some people this can be difficult if the mind is still busy – resulting in insomnia.  There are four stages of sleep (if you have a Fitbit or similar device, they attempt to identify these states whilst you are resting):

  1. Light NREM sleep.  Sometimes limbs may jerk during this drowsy state.
  2. Steady NREM sleep.
  3. Deep NREM sleep.  This is an important state for rest and repair of the physical body.  It is difficult to awaken people from this state.  Abnormal behaviour such as sleep walking and night terrors may occur during this time.
  4. REM sleep – during which time dreaming may occur.

During sleep whilst our conscious brain rests, there is a great deal going on mostly under control of the limbic brain.  The physical body undergoes repair.  The immune system is strengthened.  Memories from the day are consolidated in the hippocampus.  The brain cells are refreshed and toxins removed.  Meditation can also be very restful for the brain, but it is not a substitute for sleep.  The deep sleep NREM cycle during which time the physical body undergoes repair, does not occur during meditation.  Meditation can be more effective than REM sleep.


dreamingNearly everybody dreams, many people dream multiple times each night, and it seems that some animals may dream too.  It occurs during REM sleep when the hippocampus is active in the limbic brain, presumably processing memories.  It is a puzzle why it happens, and many in the scientific community regard dreaming as an accidental malfunction of the memory consolidation process.

For centuries, some people believe that dreams can be used to tell the future.  Certain people can have prophetic dreams foretelling future catastrophic events.  For example, in Tibetan Buddhismm, one of the high Lama’s will dream of a particular mark or sign that will be used to identify the next incarnation of the Dalai Lama.

The exact purpose of sleeping and dreaming is still not fully understood.  It used to be thought that dreaming occurred only during the REM sleep stage, but recent research  has shown that dreaming can occur during both REM and non-REM sleep.  We remember our dreams when the brain wave frequency increases in part of our brain including the Posterior Cingulate Cortex (PCC), and regions of the Occipetal and Parietal Cortex (the TPO/PTO, temporal-parietal-occipetal junction, is one particularly of interest).  This doesn’t explain “why” we dream, but does help us to distinguish basic awareness in dreaming versus awareness in waking consciousness when the AI is active.  The AI is most likely the centre for our “ego”, and our dreams can help us see what it is like to have awareness but without the ego.  The PCC is involved with autobiographical and episodal memory.  Whilst this area is active, it may mean that dreams are being formed by piecing together retrieved memories, or the reason we remember the dreams is because the PCC is being used to store the dream experience.  In which case, the source of the dream (eg from Occipetal or Parietal lobe) is still a mystery.

In my own experience I have found dreams very puzzling.  There are different types of dreams.  Most fade soon after waking, but others leave a lasting memory.  If dreams are the result of consolidation of past memories, why do I have dreams with people and places that I have never been to?  Things that I have never seen in movies or read about; things so radically different that I could not imagine them during normal circumstances.  I have had difficulty finding a scientific explanation for such dreams.

Sleep Paralysis

This seemed an appropriate point to make a brief tangent to sleep paralysis.  This is a real condition that affects a small percentage of the population.  I experienced it a couple of times in my teenage years and it was pretty scary for me at the time.  Nobody could offer me an explanation of what I experienced, but now fortunately with Dr Google it is easy to find an explanation of what was going on.

As we move into REM sleep a process called REM atonia occurs during which the muscles of the body are temporarily paralysed.  (This is important to avoid unconscious sleep walking or moving around and falling out of bed).  Sleep paralysis can occur when falling asleep or waking up.  In my case, being a light sleeper I was disturbed by a noise of a cat howling outside my bedroom window and I regained consciousness before the REM atonia process was complete.  The result is becoming consciously aware for a period of perhaps a few seconds (for some people this state may last longer, perhaps a minute or two), but being in a state of complete immobilisation.  Many people report paranormal experiences during this state, such as ghosts or intruders in the room (possibly because the TPJ in the parietal lobe and the associated sense of proprioception has not yet properly initialised and adjusted to its surroundings).  This can be due to processing in the amygdala and Thalamus structures of what they perceive to be threats.  Funny things happen in the limbic brain under certain conditions but it isn’t usually anything to be concerned about.  You can learn a lot about how the brain works internally through such experiences.