WE have at our disposal an enormous amount of material obtained by the use of the conditioned reflex method in dogs. Out of this material I shall choose three points concerning the pathological disturbances of the higher nervous activity. These are: 1) the intensity of the fundamental processes of the nervous system, excitation and inhibition; 2) the intensity in relations of these two processes, their equilibrium; 3) finally the movements, the labileness of these processes. These points constitute the basis, on the one hand, for the types of the higher nervous activity, which types play a major rôle in the origin of the so-called psychical diseases; and, on the other hand, for the characteristic alterations in the pathological conditions of the higher nervous activity.

In order to understand the pathological behaviour of man it is necessary to add to the types or temperaments described earlier by us for dogs, the special human types.

Until the time when Homo sapiens appeared animals were connected with the environment so that the direct impressions fell upon the different receptors and were conducted to the corresponding cells of the central nervous system. These impressions were the several signals of the external object. However there arises in the developing human an extraordinary perfection, the signals of the second order, the signals of the primary signals in the form of words – the spoken, the heard, the seen word. Finally it came about that through these new signals everything was designated that the human being perceived both from the environment and from his inner world, and these signals commenced to serve him not only in communicating with other men, but also when he was alone. The chief significance attached to the word was the predominance of these new signals – yet it remained a word, only a second signal of reality. And we know that there are numbers of people who operate only with words from which they deduce everything, would experience everything without coming into contact with reality. And from this they wish to base their own life as well as to direct the lives of others.

Thanks to this second signal of signals and to its constant effects in various aspects of life, all of the human race can be separated into several types: artists, thinkers, and a middle type. The latter unite in proper proportions and activity both signals [sic]. These two divisions can be seen among individuals as well as among nations.

I now pass over to the pathology.

We have become convinced in our experimental animals that the chronic pathological deviations from the normal are expressed in the excitable and in the weak type by a mild form of neurosis. The excitable animals lose almost completely the ability for inhibition; in the weak animals, the higher nervous activity is either destroyed completely or becomes chaotic. Kretschmer, who describes only two types corresponding to our excitable and our weak types, as far as I can judge, properly places the manic-depressive psychoses in the first type and schizophrenia in the second. My own clinical experience has been very limited, although I have visited regularly the neurological and psychiatric clinics for the last three or four years, and hence I offer the following remarks presumptively. Constitutional neurasthenia is a form of general weakness, occurring in the middle human type. Hysteria is the result of general weakness in the artistic type; psychasthenia (Pierre Janet), a product of weakness in the thinking type. Hysteria has to do with a general weakness especially of the second signalling signal, which in the artistic type, is normally subservient to the first signal, while in the average person the second signalling system is the highest regulator of human behaviour. Hence the chaotic condition of the activity of the first signalling system and of the emotional background occurs in the form of fantasies with unrestrained motivation and a profound disturbance of the general nervous equilibrium (now paralyses, now contractions, now convulsions, now lethargy) and the consequent chaos in the synthesis of the personality. In the psychasthenic the general weakness is also in the relationship of the organism to the environment, but in the first signalling signal, on the basis of the emotions; therefore, the lack of reality feelings, the complete incapability and uselessness, the ideas of compulsion, phobias, and the constant, distorted melancholy. Thus I conceive in general of the origin of the neuroses and psychoses and their relationship to the human types of nervous activity.

The experimental investigation of the pathological changes in the fundamental processes of the nervous activity makes possible a physiological insight into many neurotic and psychotic symptoms, including individual symptoms as well as those occurring in the symptom complex.

The weakness of the process of excitation leads to a predominance of inhibition, both in its general form and in its different partial forms, such as sleep and the many phases of hypnosis. The paradoxical and ultraparadoxical phases in the latter state are especially characteristic. To this mechanism one must, I think, refer many pathological symptoms, e.g., narcolepsy, cataplexy, catalepsy, the “sentiments d’emprise” of Pierre Janet, or inversion according to Kretschmer, catatonia, etc. The weakness of the excitatory process is produced either by its strain or by its collision with the inhibitory process.

Among the phenomena not yet altogether explainable is the alteration in the movement of the excitatory process, its pathological labileness, as seen in the laboratory. In the clinic this has been known for a long time under the name of “irritable weakness” (Reizschwache) . It consists in an unusual reactivity, in a weakness of the excitatory process followed by rapid exhaustion. Our positive conditioned stimulus in such cases gives a quick and very unusual effect which, however, during the normal time of action of the stimulus disappears; the positive action drops to zero as it becomes transformed into inhibition. Tentatively we call this phenomenon explosiveness. In our material we also find the opposite pathological alteration in the movement of the excitatory process – pathological inertia. The excitatory process persists even in the face of conditions which should normally convert it into the inhibitory process. The positive stimulation is slightly or not at all influenced by the after-inhibition of the preceding inhibitory stimulus. Such a pathological condition may result from a continually increasing tension of the excitatory process or through its collision with the inhibitory process. The relationship of such symptoms as stereotypy, ideas of compulsion, paranoia, etc., to this pathological persistence of the excitatory process is evident.

The inhibitory process likewise may be weakened either through strain or through collision with the excitatory process. Its weakening results in an abnormal predominance of delay and other normal phenomena of which inhibition is a part, expressed also in the general behaviour of the animal, struggling, impatience, unruliness, and finally as pathological phenomena, e.g., neurasthenic irritability; in man as a hypomanic or manic condition.

My collaborator, M. K. Petrova, who has enriched the experimental pathology and therapy of the higher nervous activity, during the past year has studied these phenomena of pathological labileness of the inhibitory process. A dog who formerly took food from the edge of the table is now no longer able to do this. He shies back and gets as far away as possible from the edge. The significance of this phenomenon is perfectly clear. A normal dog remains standing at the edge by inhibiting his forward movement, to a degree necessary to balance himself. Now this inhibition is strongly exaggerated. The reaction to depth being excessive, inhibition holds the dog away from the edge more than required for his interest. Subjectively this is doubtless a condition of fear; evoked and also removed, i.e., the experimenter controls the conditions of its origin.* I presume that also the delusion of persecution rests in many cases upon the labileness of the inhibitory process.

Instances of pathological stability of the inhibitory process has been observed previously by us in the laboratory.

Before us remains the difficult task of exact definition in all cases, the statement of when and under what special conditions one or another pathological alteration of the basic process occurs.

* This fact was demonstrated by Dr. Petrova for several days at the XV International Physiological Conference in Leningrad.