Articles

WHAT IS SLEEP: THE SLEEP-WAKEFULNESS MECHANISM

Attempts at anatomically localizing sleep in the brain gained increasing importance in sleep research, and efforts were made to discover which areas of the brain

govern sleeping and waking. Biochemistry similarly undertook the investigation of possible endogenous sleep-releasing substances. The idea of eventually coming upon an endogenous substance that could be isolated and that would dependably be able to induce physiological sleep of a chosen amount holds great fascination. After all, annual consumption of soporifics and tranquillizers in the Western countries alone is measured in tons.

In the process of experimentation, through stimulation of certain areas of the brain, it was in fact possible in experiments on animals to make out certain zones (somnogenous zones) in the mid-brain which when stimulated triggered states resembling sleep. It was similarly possible in other areas of the mid-brain to delineate so-called "waking centers." After the discovery of still other zones of the mid-brain relevant to the sleep-wakefulness mechanism—especially after the discovery of a brain structure extending from the medulla oblongata to the mid-brain, the formatio reticularis— interest was focused on the sleep-wakefulness mechanism that regulates the sleep-waking cycle. Present knowledge about this mechanism is as follows:

The sleep-wakefulness mechanism functions within a whole system of stimulating (activating), subduing, and diffuse nerve structures that cannot be precisely delineated. In part, these nerve structures are symmetrically laid out, and they extend from the upper end of the spine in the medulla oblongata across the mid-brain, and partially extend into the different areas of the cerebrum. This system of nerve structures, in addition to aiding the sleep-wakefulness mechanism, also assists in activating or subduing mental processes and movement (motoricity) and in regulating the autonomic nervous system that influences all these events.

The significance of this knowledge consists in the realization that there is no sleep center in the brain that acts in an isolated manner. Either it functions, in which case we can sleep; or it doesn't function, in which case we need sleeping pills. It is more accurate to state that the brain is a central organ that affects the entire organism. It constantly emits stimulating or subduing impulses that direct the functioning and activity within the organism. Areas affected include active body movements, functions within the autonomic nervous system, regulation of the functioning of the organs, breathing, circulation, sleep-wakefulness mechanism, and mental activity. In this manner, all these processes are influenced and centrally controlled. The most important characteristic shared by these brain structures is therefore a unity determined by function.

In terms of anatomy, the occipital parts of these brain structures have greater control over wakefulness, the frontal parts have greater control over sleeping. This cannot be viewed in an isolated manner, however. Similar to the feedback control system of a thermostat, it is the interaction that keeps us in the realm of normalcy.

*7\340\2*