The science of life : fully illustrated in tone and line and including many diagrams, S. 811

THE CORTEX AT WORK

§ 8 Temperament in Dogs

Finally, the dogs were not simple infallible machines but living things ; they had their weaknesses and individual peculiarities ; and here also the experiments proved suggestive from the human point of view.

It was found that in the presence of too dificult problems the normal relations between excitation and inhibition could be upset. Thus in one case experiments were being made to see how clearly a dog could distinguish shapes. The method was like that of the grey and black squares (§ 5). First a conditioned reflex was built up by heralding the food with a luminous circle, projected on to a screen in front of. the animal by means of a lantern. Then a rather flat ellipse was similarly projected, but without feeding ; and soon the animal learnt that the circle meant food while the ellipse did not. When this had been done, the shape of the ellipse was gradually altered, and it became more and more circular from day to day, in order to find out at what point the dog would begin to confuse the two shapes.

Suddenly, when the limit was nearly reached—the ellipse being about eightninths as broad as it was long—the behaviour of the dog changed. It became very excitable, and struggled and yelped in its stand ; its inhibitions disappeared, and it gave positive responses even to the first and flattest ellipse. Even outside the experimental room it remained nervous and irritable. ‘The problem had been too much for it. So the experimenters started again with the first ellipse and the circle, and retaught the old differentiation ; and as this was done the animal recovered from its nervous trouble and became quieter and more tractable. Then, even more slowly than before they began to work up to rounder and rounder ellipses. But as before, and at the same point, there was a breakdown when he problem became too difficult.

A number of other experiments were made of this kind, in which neurotic disturbances were produced by a difficult “collision” between excitation and inhibiion. In another case the animal had learnt ‘o discriminate between two different rates of rhythmic touching of the skin, one being inhibitory and the other excitatory ; then it was found that if one rhythm followed immediately after the other without any interval the machinery of the brain gave way. Or, in animals with “ weak ” nervous

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systems, experiments in which powerful natural reflexes were inhibited had similar results.

Very powerful strange stimuli could also produce neuroses. The reader who wishes to follow this matter up will find in either of Pavlov’s books! a full account of the behaviour of a dog upset by a great flood which swept through Leningrad in 1924, and in which the animals were nearly drowned.

The most interesting thing about these results is that the nervous breakdowns thus produced—which were often serious, and might last for months—were of two main types. In some animals the conflict produced a great predominance of excitation over inhibition—the example just quoted is one of these ; in severe cases the hyperexcitability was even more marked, and all of the inhibitory processes in the brain were weakened or destroyed by the clash of experimental circumstance. But in other animals the same kind of conflict unbalanced the mind in the opposite direction—i.e. in favour of inhibition. First of all the conditioned reflexes disappeared ; then after a long time they slowly recovered, but in so doing they passed through various “paradoxical”’ stages, like those seen in hypnotic states, when originally weak stimuli acted strongly and originally strong ones were weak. But each stage lasted in this case for several days.

It is obvious that these disturbances present a parallel to the nervous breakdowns or minor nervous troubles that we ourselves may experience as a result of shock, worry, overwork, or internal conflict. The human cases are discussed more fully later. Pavlov likens his two types of breakdown, in which excitation and inhibition predominate, to neurasthenia and hysteria respectively. It is interesting to note that he succeeded in curing one or two cases of the first condition by means of bromides, which, he believes in some way assist the inhibitory processes, and that, as with ourselves, a period of rest with gentle stimulations only, always proved beneficial.

In severe cases the disturbances were serious illnesses, demanding special treat-

1 Pavloy’s work is available in English in two books —Conditioned Reflexes, published by the Oxford University Press, and Lectures on Conditioned Reflexes, published by Martin Lawrence. The first is a systematic presentation of the whole field and it is written in a compressed, rather difficult style. The second is a collection of lectures, with a personal account of Pavlov. Both are for the serious reader only ; they are not light reading.

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