Activity Drives

We have found that in studying chemical motivation factors we have perforce moved into the sphere of muscle activity. Here we come face to face with the fact that tensions in the muscles are also, in all these same senses, motivators. Tension of a muscle group lowers thresholds for another contraction (as in the familiar reinforcement of knee jerks by gripping the hands). Muscle tone is constantly changing and causing new activity. Perseveration--the tendency of an activity in progress to continue beyond the period of outer stimulation, like the maddening thought that runs in the head--is a motivator of no mean significance. So, too, are the direct and indirect effects of any keyed-up condition (excitement) or any relaxed condition. Thus the muscles both guide and initiate action. The movements of the newborn are dependent alike on outer, on visceral, and on muscular stimulation.

We have suggested that the homeostatic balance is often destroyed by events which are not behavioral events. Thirst, for example, may result from sheer evaporation on a warm day, and a considerable caloric requirement must be met even when lying still. One might consequently be tempted to think of the organism as striving to maintain a sort of inactivity, remaining at rest except in periods of extreme want. The homeostasis-seeking group of villagers who have just enough energy to crawl from sun to shade; as the sun slowly moves, they supinely accept an hour or two of coolness before they are goaded again. But it would seem more appropriate to note that in terms of the tension systems which control conduct, the deficits and excesses of inner stimulation (the "too much" and the "too little") both function to cause activity. There are always many imbalances, many forms of restlessness going on. The normal condition is not one of successful escape from activity. Trends toward the reduction of activity and toward the increase of activity are always jointly manifest. The clock is always running down but always being wound up. Even when fatigue, starvation, or illness has forced a violently uncomfortable state of repose upon us, most of the bodily activities go on. The work of the body must be done. Muscular inactivity becomes unbearable; there is a compelling need to do something. At the psychological level something to do, something to occupy one's attention, is compellingly experienced. We seek repose, but we also seek activity. Broadly, the effect of all this may be conveniently summarized by saying that there are not only "visceral needs" but also "activity needs."

It may be worth while to look more closely for the reasons for such activity. Even if a given bodily tissue could carry on its life, its processes of nutrition, oxidation, and self-repair, in complete isolation from all other living tissues, it would maintain an activity level from which there would be daily or hourly variations, and it would therefore permit the notion of relative activity, relative passivity. The instant that any such tissue is considered in relation to its fellows, its activity level is seen to control to some degree the activity level of the rest, and in return to be controlled to some degree by them. The activity level is expressed in an active demand--in the sense of a great readiness to receive--for oxygen, minerals, salts, and a large and complex variety of biochemical agents such as the hormones. All tissues are in this sense active, not only competing with their fellows for a limited supply of needed substances but qualitatively directing the activity and development of other tissues. The student of embryology has long known that one tissue may "rob" another, and the student of muscular exercise has noted the same principle.

But we must go further and stress the qualitative effects which the activity of one tissue has upon the activity of another. We are dealing not simply with robbing, but with the disturbance of the balances required by other tissues, and we are concerned not only with "stimulation" but with organizing capacities. The endocrine glands, for example, act not merely to make other tissues do certain things, but to accelerate some of their many activities in such fashion as to alter the chemical balance and the physiological attributes of other tissues. From this point of view, it will not be sufficient to follow the trail from a deficit in a given region to a visible motor response. It will be necessary to consider the inner shifts which precede or parallel the externally manifested motor pattern. It is not enough to emphasize the system of muscular tensions, for we have learned more and more that the cerebrospinal axis and the peripheral nervous system, the autonomic system and the endocrines, are all parts of one great system mediating the adjustment process; there can be no chemical reaction without its effects on tension in muscle, or tension in the cerebrospinal system.

The term tension is intended literally; the concentration of potential energy under life conditions permits tension reduction. So considered, tension is also characteristic of the nervous system itself. Electrochemical activity goes on constantly in the brain (page 88); the brain cannot stand still any more than the muscles. The brain is no mere telephone switchboard; it is part of the powerhouse. There are, in a literal sense, centrally initiated motive patterns. The nervous system does not wait to be "stimulated"; it is active even under general anesthesia. Activity needs include both striped-muscle factors and cortical factors, factors involving the use of the cerebral equipment.

Although we cannot evaluate the relative intensity of these various kinds of needs, there is one hint that may suggest how subtle the needs of the central nervous system may be. It might be convenient to list the strength, the urgency, the intransigeance of the various tissues in terms of their capacity to force changes in tissues and in external behavior. In view of the current fashion of tracing motives solely to the viscera, it is rather striking from this point of view that although the viscera stand higher in the scale than do the bony and the cartilaginous parts, they are somewhat lower than the muscles and skin, and much lower than the nerve cells. The nerve cells cannot tolerate much by way of toxic effects; the blood is full of buffers which work perpetually for their protection. They can tolerate hardly any water or food shortage; delirium and incoordination appear long before the visceral processes are much affected. And they can tolerate enormously less oxygen deprivation than any other tissues. Thus while in prolonged exposure to "oxygen want" the visual disturbances are traceable both to sense-organ difficulties and to difficulties in the nervous elements in the retina, it is the nervous elements that suffer the most. The cortical needs, then, are not only urgent; they are delicately hinged upon the varying condition of the body and subtly modify all its activity patterns. The point is offered merely as one more suggestion of the artificiality of the current attempt to make the mainsprings of human motivation reside in the unstriped muscles, the glands, the arterial walls, the gastrointestinal tract, or any other visceral structures. These are all of importance, but they are not the only important ones; it would indeed be hard to justify designating them as the most important of all.

The activity needs, probably traceable to tensions both in the nervous system and in the striped and unstriped muscles acting jointly, dominate a large share of the small child's waking hours. Infants may kick when hungry, thirsty, or cold, but they also do a good deal of kicking and rolling, a good deal of wriggling and smiling, when not in any manifest state of visceral need. The little child keeps himself active, knows nothing worse than to have to keep still, just as the adult begins to feel below par when activity is allowed to fall to too low a level. If there is a need to eat, there is in exactly the same sense a need to use all of one's physical machinery. Under the activity needs we should of course include the need to relax and to sleep. And we should also include activity cycles, up-and-down swings of the type to which the term "rhythmic" is applied, and symmetrical or balanced activities, such as those involved in the maintenance of posture and in locomotion. There is a physiological continuum from the sheer inability to sit perfectly still to those compelling needs of activity and creativeness to which progressive education gives so much attention.

Activity needs show summation as clearly as do visceral needs, many different centers of tension combining to throw us into overt activity. A given tension level results from the summation of many factors, but there is a center of maximal activity, as in the golfer's arms as he drives, the rest of the muscular system playing an abundant supporting part. In turn, activity drives may facilitate visceral drives, or vice versa. The energies of the happy, excited childhappy whether it be birthday ice cream or the expectation of a prize at school--tend to "spill over" into visceral or into striped-muscle expression. As far as is known, any stimulus whatever tends to raise the tension level; tension anywhere spreads to some extent to other regions.