From time immemorial, the subject of sleep and dreams has intrigued man. Sleep enraptures people because it may be somewhat reminiscent of death: we lie down, we close our eyes and we are dead to the world.

It appears that, only a few minutes later, without being aware of any loss of time, we get up again. Sleep is an occasion that expresses the subjective vision of not happening at all.

We are not conscious of having slept.
* Sleep is a non-activity that seems to steal one-third of our life.

Dreams - usual part of sleep, they can be very worrying and can even make us question our sanity.
In the past, a veil of mystery has covered the subject of sleep and dreams. Modest objective knowledge about the nature of sleep and dreams was available.

Information about sleep was accessible, represented a murky mixture of facts and mystified conclusions, mired in superstition.

Sleep - condition of semi-consciousness, causes anxiety because sleep reduces our environmental perceptions and degrades our ability to respond to danger. We are anxious because we realize that we are very vulnerable while we are asleep.

Sleep involves the interruption of most of our sensory input and a reduction in most of our physiological processes: We are not aware of ordinary sounds; we close our eyes in order to eliminate visual input.

Consider the physiological level, our limbic nervous system slows down our breathing rate and our heartbeat; it even reduces our blood pressure. Our autonomic nervous system limits the production of waste products in order to prevent disruptions to our sleep.

Whereas our physiological functions operate at a minimal level, our brain also adjusts itself to reduced sensory input and operates on a very primitive level.

While we try to probe the mysteries of sleep, we are only moderately concerned with the changes in our physiological functions while we are asleep.

Finally, these functions are readily discernible and are fully under the automatic control of the autonomic nervous system. We are really intrigued by the mechanics of sleep as it affects our brain and, therefore, our mind. 

So, what are the functions of our brain while we are asleep?