When this irritation along a certain nerve path is oft repeated or quite constant, we have a consequent repetition of the defensive reaction, whatever it may be. This performance may be so frequently repeated that the idea of irritation or mental conflict or the anticipation or the expectation of a repetition of same may be quite sufficient in itself to arouse this reaction. It may become so habitual that, even though no such idea be in the mind, there may be a repetition of the movement whenever the individual is nervously excited or upset, whenever there is any mental stress, strain or discomfort. And we may go even further and say that as a result of some unusual mental struggle, some excessive mental strain, defense or adaptation is brought about by regression or resort to a tic, this being conditioned by the fact that for the particular individual under discussion this is the easiest, most convenient or most immediate form of reactive response. The discharge is, as is seen, along the line of least resistance. This line of least resistance is determined by the organic nervous constitution and by certain life-experiences or habit-formation factors. In some cases the movement, once initiated, may be continued long after the disappearance or cessation of the external irritation, because of the sense of relief or satisfaction or pleasure[*] which is obtained by the performance of the tic. In many instances the habit has become rather fixed, and, as a relief from the struggle to do or not to do the movement, and because of fatigue in the effort to inhibit or control the movement, the individual adopts the path of least resistance, best for immediate relief from mental struggle; and as a psychobiological effort at self-preservation and self-gratification, as immediately as possible and at any cost to be paid in the future, he gives vent, as it were, to the movement.
[*] This is not, of course, of a sexual nature the Freudian school notwithstanding.
The psychic symptoms may come on at a later date than the motor symptoms or simultaneously, although, of course, the early life history, in childhood and puberty, for example, if we are dealing with an adult, may show, at least in a certain proportion of cases, that the individual was of a psychopathic type, perhaps somewhat shut-in or asocial. If the appearance of the psychical symptoms be simultaneous with that of the physical symptoms, we can understand at once how, like the motor symptoms, they may be repeated time and again. In many instances, at least, the psychic symptoms arise later, being added to the motor symptoms. These later psychic symptoms may be a direct reaction to the source of irritation, or may be occasioned by the dissatisfaction at being unable to control the movement in question.
The degree of reaction, its duration and severity, depend upon the hereditary and developmental make-up of the individual and the severity, frequency and duration of the irritation, physical or psychical. The psychic element is particularly apt to vary. The more neuropathic and psychopathic the make-up the greater is the reaction.
Where mental enfeeblement or mental disorder exist, the severity and chronicity are apt to be still greater.
There is thus a fixation, or rather a regression or reversion, oft repeated, to a type of reaction of a very infantile, primitive sort, farther down in the scale of evolution and development.
This picture may be further complicated by so-called neurasthenic, psychasthenic, hysterical or other reactions. Naturally one would expect to find these conditions, especially the more aggravated forms, in individuals of a neuropathic and psychopathic family strain, and who themselves are neuropathic or psychopathic or both.
It may be mentioned here, as is clearly appreciated from what has been said before, that there is an interrelationship between the tics on the one hand and the symptoms which we discover in the psychoneuroses, psychoses and the mentally unstable on the other.
In all of these conditions we find a cortical origin for the disturbance, there is a lack of will power, of inhibition and of control of the lower centres, there is a nervous and mental instability with a tendency toward regression or dissociation, and the assumption of more or less independent, almost automatic activity, this activity being characterized by its almost (relatively) infantile, primitive, archaic makeup.
Were I to take up any one of the tics as an illustration, this general idea could be applied very nicely. But I shall not present any illustrative cases in this paper. I shall leave it to the reader, however, to explain the genesis and evolution of, for example, facial tics (which are so common) from this standpoint.