The science of life : fully illustrated in tone and line and including many diagrams, str. 809

THE CORTEX AT WORK

surroundings, to a deliberately simplified environment, for reasons that we have already noted, and there were less stimuli than usual to keep their brains busy. Accordingly the excitatory processes, which normally prevail against inhibition, were lessened. The balance between inhibition and excitation was upset; the former got out of hand and spread itself over the brain much farther than it would in the normal varied doggy life.

This identity is one of the most suggestive ideas that has emerged from Pavlov’s work, for it seems to foreshadow an analysis of all sorts of subtle fluctuations in the vigour and acuteness of our minds. Mr. Everyman probably imagines that he divides his twenty-four hours between wakefulness and sleep, but in fact, as these investigations demonstrate, he is never completely awake. There are always bits of his brain that are calmly slumbering. Whenever he decides not to perform and defers some natural act, and so inhibits a conditioned or unconditioned reflex, he is literally putting a part of himself to sleep, so that in a sense sleep is a necessary and integral part of his waking activity. Conversely, when most of him sleeps, little bits of his brain may stay awake. Let him note as an illustration how his sleeping wife, although she cannot be roused by a host of accidental noises, may wake up at once at the feeble cry of her sick child. Sleep is everlastingly ebbing and flowing in the brain. With the coming of night it wells up, with the coming of day it recedes, but only in very rare moments, if at all, does it drain away altogether from the hemispheres.

87 The Dog Hypnotized

And now we turn to certain strange halfway states between sleeping and waking that occasionally appeared during the experiments. In rare cases, the dog would sink into a “trance”; it would stand in an erect, alert posture but perfectly motionless, sometimes for minutes, sometimes for hours. In this condition there was no sign of the limpness that accompanies true sleep, but there was also no sign of active control. If the limbs were moved into a new position by the experimenter the animal would “stay put” in the new attitude.

The condition is apparently intermediate between the strictly localized inhibition of normal activity and the complete diffusion of sleep. All the control centres in the

cortex are asleep, but the lower reflex centres which keep the body erect and balanced (Book 1, Chap. 3, 86) are still in full activity.

Or the inhibition may be even more local, and affect a part only of the cortex. Sometimes the dog is immobilized as far as its muscles are concerned, but still in control of its glands. Then a strange spectacle may be witnessed by peering in through the window of the experimental-room. The dog stands “entranced”; presently a metronome begins to click (or whatever conditioned stimulus has been used for the particular animal is brought into action) and at once there is copious salivation—but without the slightest sign of any movement to interrupt the fixed poise of the “ trance.”

These experiments throw light on that puzzling department of human psychology, hypnotism. One of the first expressions of hypnosis is the ‘“‘ cataleptic state ’—a state of immobility in which voluntary control is lost, but the power of balancing and holding up the body retained. Evidently this corresponds to the partial sleep of the brain that is sometimes seen in dogs. The subject, like a dog, may have part of his cortex awake and part inhibited; being unable to control his limbs and remaining in any position in which he is put, but all the while fully realizing his own helplessness. As a further parallel between dog and man we may note how closely the passes and reiterated formule with which the hypnotist “puts his subjects under’? resemble the monotonously repeated stimulus which was found to be so powerful an initiator of inhibition in the animals.

Throughout the animal kingdom, even in invertebrates, similar phenomena can be traced. If a crayfish is held in one hand and stroked somewhat firmly along the back of its carapace, from tail to face, it will pass into a cataleptic state, which bears a suggestive resemblance to that seen in dogs or men. It becomes motionless and its muscles have a stiffness that has been compared to the stiffness of wax. In this state it can be put into the most grotesque attitudes, and will hold them until the inhibition passes off. Frogs can be thrown into the same condition by stroking, or by holding them between the two flat hands so that they cannot move, and then suddenly turning them on to their backs. Indeed, a great variety of creatures can be similarly immobihzed—goats and pigs, ducks and hens, crabs and water-scorpions. The Indian snake-charmer knows’ that if a cobra is

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