The Story of the Mind

by James Mark Baldwin

1. Method of Extirpation.—This means simply the cutting away of a part of the body, so that any effect which the loss of the part makes upon the mind may be noted. It is used especially upon the brain. Pieces of the brain, great or small—indeed, practically the whole brain mass—may be removed in many animals without destroying life. Either of the cerebral hemispheres entire, together with large portions of the other, may be taken from the human brain without much effect upon the vital processes, considered as a whole; the actual results being the loss of certain mental functions, such as sight, hearing, power of movement of particular limbs, etc., according to the location of the part which is removed. Many of the facts given below under the heading of Localization were discovered in this way, the guiding principle being that if the loss of a function follows the removal of a certain piece of the brain, then that portion of the brain is directly concerned in the healthy performance of that function.

2. Method of Artificial Stimulation.—As the term indicates, this method proceeds by finding some sort of agent by which the physiological processes may be started artificially; that is, without the usual normal starting of these processes. For example, the physician who stimulates the heart by giving digitalis pursues this method. For psychological purposes this method has also been fruitful in studying the brain, and electricity is the agent customarily used. The brain is laid bare by removing part of the skull of the animal, and the two electrodes of a battery are placed upon a particular point of the brain whose function it is wished to determine. The current passes out along the nerves which are normally set in action from this particular region, and movements of the muscles follow in certain definite parts and directions. This is an indication of the normal function of the part of the brain which is stimulated.

Besides this method of procedure a new one, also by brain stimulation, has recently been employed. It consists in stimulating a spot of the brain as before, but instead of observing the character of the movement which follows, the observer places galvanometers in connection with various members of the body and observes in which of the galvanometers the current comes out of the animal's body (the galvanometer being a very delicate instrument for indicating the presence of an electric current). In this way it is determined along what pathways and to what organs the ordinary vital stimulation passes from the brain, provided it be granted that the electric current takes the same course.

3. Method of Intoxication, called the "Toxic Method."—The remarks above may suffice for a description of this method. The results of the administration of toxic or poisonous agents upon the mind are so general and serious in their character, as readers of De Quincy know, that very little precise knowledge has been acquired by their use.

4. Method of Degeneration.—This consists in observing the progress of natural or artificially produced disease or damage to the tissues, mainly the nervous tissues, with a view to discovering the directions of pathways and the locations of connected functions. The degeneration or decay following disease or injury follows the path of normal physiological action, and so discloses it to the observer. This method is of importance to psychology as affording a means of locating and following up the course of a brain injury which accompanies this or that mental disease or defect.

Results—Localization of Brain Functions.—The more detailed results of this sort of study, when considered on the side of the nervous organism, may be thrown together under the general head of Localization. The greatest result of all is just the discovery that there is such a thing as localization in the nervous system of the different mental functions of sensation and movement. We find particular parts of the nervous organism contributing each its share, in a more or less independent way, to the whole flow of the mental life; and in cases of injury or removal of this part or that, there is a corresponding impairment of the mind.

First of all, it is found that the nervous system has a certain up-and-down arrangement from the segments of the spinal cord up to the gray matter of the rind or "cortex" of the large masses or hemispheres in the skull, to which the word brain is popularly applied. This up-and-down arrangement shows three so-called "levels" of function. Beginning with the spinal cord, we find the simplest processes, and they grow more complex as we go up toward the brain.

The lowest, or "third level," includes all the functions which the spinal cord, and its upper termination, called the "medulla," are able to perform alone—that is, without involving necessarily the activity of the nervous centres and brain areas which lie above them. Such "third-level" functions are those of the life-sustaining processes generally: breathing, heart-beat, vasomotor action (securing the circulation of the blood), etc. These are all called Automatic processes. They go regularly on from day to day, being constantly stimulated by the normal changes in the physiological system itself, and having no need of interference from the mind of the individual.

In addition to the automatic functions, there is a second great class of processes which are also managed from the third level; that is, by the discharge of nervous energy from particular parts of the spinal cord. These are the so-called Reflex functions. They include all those responses which the nervous system makes to stimulations from the outside, in which the mind has no alternative or control. They happen whether or no. For example, when an object comes near the eye the lid flies to reflexly. If a tap be made upon the knee while one sits with the legs crossed the foot flies up reflexly. Various reflexes may be brought out in a sleeper by slight stimulations to this or that region of his body. Furthermore, each of the senses has its own set of reflex adjustments to the stimulations which come to it. The eye accommodates itself in the most delicate way to the intensity of the light, the distance of the object, the degree of elevation, and the angular displacement of what one looks at. The taking of food into the mouth sets up all sorts of reflex movements which do not cease until the food is safely lodged in the stomach, and so on through a series of physiological adaptations which are simply marvellous in their variety and extent. These processes belong to the third level; and it may surprise the uninitiated to know that not only is the mind quite "out of it" so far as these functions are concerned, but that the brain proper is "out of it" also. Most of these reflexes not only go on when the brain is removed from the skull, but it is an interesting detail that they are generally exaggerated under these conditions. This shows that while the third or lowest level does its own work, it is yet in a sense under the weight—what physiologists call the inhibiting action—of the higher brain masses. It is not allowed to magnify its part too much, nor to work out of its proper time and measure. The nervous apparatus involved in these "third-level" functions may be called the "reflex circuit" (see Fig. 2), the path being from the sense organ up to the centre by a "sensory" nerve, and then out by a "motor" nerve to the muscle.