WHY DO WE SLEEP?

Hauraki Plains Gazette, Volume XXXIX, Issue 5330, 24 September 1928, Page 2

WHY DO WE SLEEP?

STUDY OF THE CAUSES. PHENOMENA OF SLUMBER. This is a very difficult question and none of tlie. answers that have been suggested can be said tq command general assent. It i not difficult t,o point out tlie utility c,f sleep, for living, applies a running-down of the clOjCk and sleep is a t>ine for windit up writes Professor J. Arthur Thomson in “John o’ Loudon. Sleep affords, opportunity to accumulate savings, for another bc,.iii.t of energetic spending. As Professor Halli" burton says in his well-knowp Handbook of Physicjogy, whi«h has passed through 16 editions or more, “Sleep is the period of anabolism, repair, and growth. Loss of sleep is more damaging than starvat.qn. But the need for rest, and repair does n,ot explain hew it is that we become sleepy. Moreover, c ; ur spinal cord never gees asleep, .and the medulla oblongata is never more than a little somnolent; so why should the higher parts of the nervous system require a. rest that, the other parts ilq not demand ? Moreover, the hard-worked heart, never stops—except momentarily —till it. can beat no more ; and our breaching movement continue in our deepest slumber, sometimes, with vibrations of th - sof.t palate that, are; obtrusively obvious to. others, though all but unknown to ourselves. If the heart can gq on beating for three score years and ten why should our cerebral hemispheres, which we rarely work so hard, demand a 10-ng rest every 24 hours ? And aga ; in for the great majority ©if an.imals sleep is quite unknown, and many never, even c’ondercend to take a rest. There are some- animals that pass into a state of inertness when they are lifted off the ground, and this ha,s been attributed to the sudden shutting off of the current of impressions, that normally serve to keep the creatures active. So some unhealthy people fall into a sleep-like state whenever they' shut their eyes, thus excluding the n,ews that usually kept them awake. . .

If we disconnect our bodily telephone by shijtting our eyes and by closing the, shutters of our room, there are few external calls to keep us awake, though there may be sleep" banishing disturbances- within the bodily house; itself. It is slafe to ( say that one of the conditions of sleep is a diminution, in the number of afferent. impulses that usua.lly force their way into our central nervous system.

Another factor is habit.; and that is bound up, in a great part of the globe, with the regular alteration of day and night. From infancy qnwards the habit of sleeping hast grown onus, a,nd the organism is readily amenable to the establishment, of rhythms. The more metho/lical our habits of going to; bed, the more likely are we, to sleep soundly. This sometimes becomes curiously complicated by the establishment of “conditioned reflexes,” or associations. That is to say, certain stimuli, such as a lullaby for the child, a night-cap for a man, become inextricably linked on the habit of falling, asleep; and they may often a.ssist in enforcing the rhythm when external conditions are hot pronitious.

Many of us say to ourselves that we fall asleep because we are tired, and this is one of the favourite theories qf sleep—a biochemical thec-ry. For being tired probably means that certain, specific toxins or poisons are formed by particular forms of hard work, by nervous activity in, particular, and these toxinh accumulate in the blood until they begin to inhibit, or paralyse the higher nerve centres associated with consciousness. That is pot, indeed, so far. as we can see,an y necessity for this; for. the body is continually masking and filtering out the poisonous waste products which it manufactures!, and why should it. not. do the same rapidly for the sleep"producing toxins which are assumed to disap" pear in our slumbers, especially during the first two hours 7‘But, it may be sufficient to answer, that the periodic enforcement of rest is for va.ricus reasons so. very useful that a slow way of dealing with certain nerve-toxins has been tolerated.

One of the arguments in .fayour of the theory, or perhaps hypothesis is a more accurate word, of a sleep-pro-ducing fatigue"toxi.ni is the. experiment of iiijecting into a fresh animal some of the bicjod of another that is falling asleep with extreme overexertion. The injection is said to be immediately fo,Howel by de e P sleep. There is no doubt that the wheels off ...the sleeping body/are not going round So quickly as in w.a,king hours ; yet digestion goes on, breathing movements do nqt cease, .the beating of the heart coinjtinues, the filtering of the blood proceeds, the muscles, fortunately, do not cease to produce heat and they remain! in a state of gentle tensionr, or tonus. In betwixt and between—e.g,., human — cases, where some of the higher centres 'of the brain dm not fall asleep, there is the po/sibility of mc.ving about —to wit, somnambulism. After a period of lowered brain circulation, associated 1 with tiredness and much reduced reactivity, there is in the first hour oi- two of refreshing slumber an increase in l the flow of blood to the brain, and this probably implies a sluicing out cjf inhibiting toxins. Bu the. central .fact about sleep is the relative interrupion of the ordinarily eentiuous consciousness. This is- what separates sleep so markedly from a profound rest. Apart from dreams, which are mostly very rapid, we spend about a third of our life in a state, of unconsciousness.

Nq d’oubt many of the lower animals take tong rests, like .the queen bumble bee throughout the winter, but this red. is far away from what we know as sleep, and the same must be said of hibernation. This brings us to our theory that sleep is an in* hibition of mental activity, or of the higher brain centres; by a particular nerve-, to.xin, which is chiefly produced in the more intelligent animals.

So far as we know, a relatively stupid mammal like a guinea pig qevqr falls asleep. But sleep cqnquers the highly evolved intelligence off ,the flog and the horse ; and both of them dream I