Role Of Deep Sleep

We saw that Deep sleep appeared about 180 million to 130 million years ago in mammals as they evolved from reptiles. And that during Deep sleep the body's muscles are relaxed and heart beat and breathing are slow and regular. In Deep sleep 'one is not dreaming but thinking'.

As reptiles evolved into mammals and mammals into human beings, complicated and interrelated physiological and biological changes took place. And it seems as if body maintenance and development takes place during Deep sleep.

For example, "during sleep, the endocrine organs come to life and secrete into the bloodstream hormones that affect the entire body" .

Role Of REM Sleep

"If REM sleep is prevented, it takes precedence over other kinds of sleep until the lack of REM sleep has been made good, at least to some extent. So human beings need REM sleep."

Professor Lavie heads Haifa Technion's Sleep Laboratory. He reports "that in some way or other, we can maintain contact with reality during REM sleep and even decide when to wake up with the help of internal signals", and that "REM sleep allows a smooth and rapid transition from sleep to wakefulness, and so can be viewed as a gate to wakefulness during sleep."

"Further findings at the Technion Sleep Laboratory demonstrated an additional advantage in awakening from REM sleep. When we examined how people functioned after awakening from REM sleep, we found that they performed very well at tasks which included orientation in space. These tasks, which are controlled by the right hemisphere of the brain, were performed with a lesser success rate after awakening from the Deep sleep of stages 3 and 4. In other words, a person awakening from REM sleep is immediately orientated in his surroundings, which is of cardinal importance to a smooth transition from sleep to wakefulness."

Which suggests to me that the left hemisphere is involved in Deep sleep 'dreaming' and the right hemisphere in REM sleep dreaming.

REM sleep appeared when, as we saw already, mammals evolved into giving birth directly from the womb, their young being born alive after having been developed for a considerable period within the womb. The young have to grow and learn much for a long time before they can survive independently, for many years in the case of human beings. Which applies particularly to the brain which now has much greater learning capacity.

During the first few days after birth the actual amount of REM sleep is very great and Lavie concluded that "it plays a vital role in the maturing stage of the nervous system" and that "it is possible that REM sleep is particularly important for procedural types of learning in which humans acquire motor and perceptual skills. Since during the first few months of life infants are busy acquiring new motor and perceptual skills, these findings may also explain the abundance of REM sleep at that particular time in our life".

Lavie also reports that REM sleep in cats "seems to be training their neural networks in mainly instinctive behaviour" and that "several studies have indicated a possibility that the consolidation of memory traces for at least certain types of learning occurs during REM sleep".

So the role of REM sleep appears to be that of generating dreams, of filing away memories for later use, and to enable us to wake up quickly and fully orientated.