Issues in Biology

Sleep, Dreams, and Consciousness

Sleep is undoubtedly one of the most important factors structuring our lives. The necessity for animals to sleep, and the concomitant problems associated with a lack of sleep have a tremendous effect on our ability to function on a daily basis. While the role of sleep as part of the physiology of our body is entirely elusive, the results of the lack of sleep are well documented. The question of how sleep works at the molecular level is subject to a tremendous effort in basic research. Clearly, the metabolism of the brain is instrumental to the control of sleep-wake pattern including the importance of neurotransmitters, hormones, and brain specific lipid components of neuronal and glial cell membranes (neurons and glial cells are the major cellular constituents of our brain). These are the same structures identified in various brain functions for cognition, motor control, speech, memory and consciousness. Five stages of sleep have been described at a phenomenological level with the REM stage (the fifth stage; rapid eye movements) being the most widely known. That these stages are characterized by such properties as the speed of eye movements, duration, how easy it is to awake from it, or if we remember dreams, is typical for sleep research. Sleep is mostly studied as a clinical syndrome, which is obviously important considering the widespread occurrence of sleep disorders. The difficulty in understanding the underlying biological mechanisms of sleep is exemplified by the observation that although sleep is correlated to the presence and absence of certain chemicals, it cannot be simulated by anesthesia, a state of unconsciousness from which we cannot wake up (certainly due to the presence of the anesthetics). General anesthetics block the activity of brain chemicals involved in active signaling and sleep is characterized by a very active brain exhibiting typical brain wave patterns that differ both from a wake or anesthetized brain. Sleep deprivation impairs cognition, learning, memorization, and over prolonged periods kills. Sleep is necessary for normal functioning of the brain. Sleep deprivation, before one dies, causes hallucinations, mood swings, loss of memory, and impaired physical performance. An interesting effect of the immune system on the brain is well known. Strong immune reactions to fight of an infection cause drowsiness and sleepiness, possibly to slow down physical and mental activity to make metabolic energy available to the immune system. One class of immune system hormones, the cytokines, are instrumental in this synergetic mechanism between the immune system and the brain. 

For what has just been described, sleep is one of two fundamental brain activities that to this day are hard to come by with a reductionist or molecular approach. We face complex functions of a very complex structure, the brain. Here is the interesting issue; both consciousness and sleep are the product of one and the same organ and controlled by the same signaling mechanisms. Yet they 'work' in seemingly opposing ways while strongly influencing what makes us human, our self, our culture, or the perception of time. Sleep has been described as a purging mechanism unloading unnecessary information (through dreaming), reinforcing memory, or improve learning. All these explanations are widely speculative, for the mechanisms of these properties of consciousness are themselves poorly or not understood, neither at the molecular nor physiological level. How could we understand the way sleep affects memory and learning? One fact is certain, the questions surrounding sleep have captured the attention of many bright scientific minds, as has consciousness. That both phenomenon are related can be concluded from their intimate relationship with the same biochemical structures. The latter believe is certainly the driving force to undertake molecular studies and combine biochemical, neurological, and psychological research to gain a complete understanding of how the human brain produces consciousness and how our body uses both wake and sleep stages to maintain the brain's biochemical homeostasis.

More information about sleep can be found at the National Institute for Neurological Disorders and Stroke, NINDS , a division of the National Institute of Health of the US Government.

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