Practically all physiologists start with an implicit or explicit assumption which is something like this: that all the phenomena of the behavior of living organisms are compatible with a mechanistic interpretation of the universe. In other words, living organisms in their behavior are physicochemical machines, and the future behavior of living organisms is determined by their total past experience and the totality of present affects upon them. This is, of course, not a new or original hypothesis. It has been arrived at through the ages, from the time of Democritus, through Spinoza, von Holbach, Huxley, to Santayana at the present time

The concept of mechanism is going out of style today, largely because of a misinterpretation of the Heisenberg principle of indeterminism. There’s a mechanistic interpretation of the universe and scientists often subscribe to it for at least two reasons: in the first place, because it is heuristic. Second, because a mechanistic theory which is thoroughgoing and not oversimplified is compatible with many of the phenomena which transcend mechanism.

Perhaps it might be well if we elaborated on this. We all have some model in the back of our minds of the machinery of human behavior. Let me be bold enough to present my particular model, recognizing that it is naive and oversimplified, because it may form a basis of discussion. In many ways, this model of human behavior has a great deal in common with the Bostonian’s map of the United States. It overemphasizes those areas with which I am familiar and underemphasizes others. This mechanism may be likened to a steam engine which is energized by a fire consisting of the oxidation of glucose, glucose and oxygen going into the brain by way of the cerebral circulation and reacting there. Other substances represent in mass a very small quantity of material; nevertheless, they may be extremely important in the regulation of the flame and in the continued development and repair of the whole machine.

The flame heats a boiler and turns a flywheel. This we may call the Krebs cycle. Energy from this flywheel passes through a clutch mechanism, which can be regulated to increase or decrease the efficiency of transmission of energy from this flywheel to another one. This clutch is the mechanism of phosphorylation, or the creation of high-energy phosphate molecules from the energy released by oxidation.

We may now put into the system a dynamo, generating electrical energy. This energy becomes stored in a battery, which represents the piling up of certain chemical constituents of the cell which are high in energy content, the so-called energy-rich phosphorus compounds. From this storehouse there is a more or less continuous How of electrical energy to the thinking or integrating functions of the brain, which can be naively represented by a series of electronic tubes, hooked together in such a way as to constitute a magnificent electronic computer.

Someone has said that paranoid schizophrenics and scientists have one thing in common in their behavior: their preoccupations change with the development of technology. Several centuries ago the brain was a hydraulic engine, then it became a telegraphic machine, then it became a telephone switchboard, and now it is an electronic computer.

Going into this computing machine are a number of input leads from the ear, which can be designated as a microphone; from the eye a photo cell; from all the senses, but these two will be sufficient.

There is another device which selectively stores the events which take place in the rest of the machine, some tape recorder or other more sophisticated gadget. It is called memory. Within this machine, then, is the entire universe of its experience, past and present.

Finally, the output of that machine, integrated in all its parts, results in behavior, which is largely a function of muscular activity.

This, admittedly naive, representation of the mechanism of behavior nevertheless embraces cerebral metabolism, and also biophysics, neuroanatomy, the social sciences, psychology, cybernetics, and so on.