The Physiological Basis of Motivation

Our analysis of motivation suggests rather clearly two distinct physiological problems. In the first place, the conditions in the various bodily tissues which provide the stimulating and dynamizing effect upon overt response must be identified and studied in detail. In the second place, the manner in which these tissue conditions become connected with specific determinants of response must be ascertained. The first problem obviously lends itself to direct experimental attack more easily than the second. In fact, the physiological study of basic tissue activities has more or less kept pace with the psychological analysis of their importance in behavior. But in an understanding of the relation of specific response determinants to these basic tissue conditions, the psychologist is far ahead of the physiologist.

There is, of course, a very good reason for this discrepancy. The psychologist may relate motives to positive and negative reactions toward specific external goals; but the physiologist must confine his descriptions solely to neural principles, many of which are not yet clearly understood. Just as the primary motivational excitants can only be represented by sources of energy in the various tissues on a par with external stimuli, so their relation to the determiners of response-specificity must rest largely upon the special sensitiveness of the reacting mechanism to this particular influence. The manner in which this sensitiveness is acquired must be analyzed in neural terms; it cannot be assumed to have just happened that way.

All behavior is controlled through the neuromuscular mechanism, the body moving only because this system is activating it in a given manner. Operating originally in a random fashion in response to the motivational excitants, the neuromuscular apparatus soon achieves rather specific ways of equilibration. More than this, it is capable of elaborating and of modifying these forms of response almost endlessly, the residua of such changes being carried by modifications of the neural tissue. Experimental as well as theoretical analysis must be made of the neural dynamics here involved.

The physiological explanation for an animal's specific reaction to a given stimulus complex [internal and external] lies in the recognized nature, and inevitable interaction of the various factors in the situation. Given a nerve arrangement constituted thus and so, it must be set off by a certain stimulus complex and, when set off, it must lead to the reaction which is seen to follow. The necessities of the process will appear to be similar to those of the movement of an automobile when the motor is started, and the gears and clutch are engaged. When we have completely envisaged this mechanical system, we shall be able to see whether there is probably any outside guiding agency, as there usually is in the case of an automobile, or whether the mechanism is entirely automatic-which is easily conceivable.