Psychotherapy exercises its potentiality as a therapeutic resource by its influence upon human experience. It is the conclusion of monism that processes of experience and brain processes belong to the same thing, as different aspects of its one and the same action, and that this thing is neither brain nor mind, but reality - the organism in function. A different brain change occurs for every difference of experience.

In the study of the nervous system we find for every difference of experience - whether of quality, intensity, or structure - a corresponding physical change. The end sought in psychotherapeutic treatment is to bring the patient under the influence of such experiences as will produce such brain changes that will promote the normal functionating of the organism on the one hand, and that will serve to adapt the individual to his environment on the other.

Every process of experience, state of consciousness, or condition of mind is associated with corresponding organized physiological processes or physical changes, which are the results of such experiences upon the neuron elements. Psychic traits, dispositions, or qualities of personality or mentality are acquired by experiences coming at some time within the life of the individual, and they do not exist apart from the functions of the nerve and brain cell. To think of a quality of personality as existing apart from the functions of the nerve and brain cell is folly. The neuron and its activities constitute the basis of all psychic action. Neurosis and psychosis go hand in hand. No neurosis, no psychosis; no psychosis, no neurosis. That every psychical phenomenon has its physical concomitant is the well-established basis of physiological psychology.

We account for the results of psychotherapeutic treatment as we account for other processes of experience. Every process of experience implies two sets of conditions - the occasion or the stimulus on one hand, the reacting structure on the other. The occasion or stimulus may be mental or physical, and we are about to see how a physical stimulus can be understood to act upon the mind and experience, and how these can be understood to act upon the body. The reacting structure is the mind, and, in assuming that it has its physical correlate in the structure of the nervous system, there accordingly it is open to description and explanation like other physical structures.

Our entire experience, and that of the lower forms of life as well, presents a growing complexity of structure and a deepening psychophysical unity. Of the mind, as of other things, there is no saying what it is by itself apart from all its connections. So long as we regard it in connection with the functions of the neuron, we are on a scientific basis.

We know the mind, as we know other things, by what it does, and we are thus enabled to reason from cause to effect. What it does is to always experience - to both act and react under the influence of innumerable internal and external stimuli; and whatever it does, consciously or unconsciously, designedly or unintentionally, must be revealed in experience, just as the most invisible works in nature are revealed in sensation.

The nervous system faithfully conserves and reproduces its experiences, and all experiences, however and whenever formed, if conserved, are a part of ourselves and belong to us as an essential part of our personality. Try as we will, we can not get away from the influence of past experiences in the determination of what we are today. We can modify, change, or neutralize the effect of our experiences to a considerable extent, but we can not destroy them. Every experience retains the right to express its influence in our later life. Conserved as they are by the nervous system, they represent in reality living, active forces operating for the good or harm of the individual.

The experience of our forgotten childhood and youth, even those of infancy, lives actively in our adult years, and contributes to the formation of that variously named portion of our mental lives of which we are not consciously aware. The study of this portion of our mental lives - repressed, yet active - constitutes one of the most interesting phases of psychotherapeutic treatment, the importance of which is not justly appreciated at the present time.

While inheritance plays an important part, and varies within wide limits, in making us what we are in mind and body, the most important factors are the influences to which we are subjected after birth. This is not to depreciate the importance of what we bring into the world as a hereditary endowment, but to emphasize the importance of education and training after we are born.

If we would change the mental and physical constitutions of an individual, bring him under the influence of such experiences as will bring about such modifications or changes as are desired. All experience, however and whenever acquired, is education, and, whether its influence is for good or ill, it should be given a broader meaning than is usually accorded it. While the influence of all experiences of the past are ever active in the various functions of the psychophysical organism of man, it is never too late to bring him under such experiences as will modify, influence, change, inhibit, or encourage the functions of the nervous system set into operation by previous experiences. To bring about such changes as will result in the upbuilding of the physiological and mental constitutions of our patients, where such help is needed, is the function of psychotherapy.

Munsterberg remarks: "Theoretically, the field in which psychotherapy may work on both mental manifestations and bodily functions is a large and interesting one, but it is- still open to little real understanding. The explanation has essentially to rest on the acceptance of a given physiological apparatus. A certain psychophysical excitement produces by existing nerve connections a certain effect, for instance, on the blood vessels or on the glands of a certain region, or on a certain lower nervous center. That such an apparatus exists, the physiological experiment with the employment of suggestion with persons in the normal waking state or in hypnosis can easily demonstrate."