Rats ran an alley and pressed a lever for brain stimulation reward. At the end of the 10-min. intertrial interval, they received pretrial priming stimulation. Varying the amount (number of trains and number of pulses) of stimulation showed that both the lever-produced stimulation and the pretrial stimulation affected running speed. The 2 effects, however, had different parametric characteristics. An analysis of the transitional responses following changes in the amounts of stimulation further showed that one effect involved a memory for stimulation received on earlier trials, whereas the other effect did not. The experiment provided a paradigm for independently analyzing the 2 effects. A second experiment showed how this paradigm may be modified to permit automation of the entire procedure.

PrefaceThis book was conceived many years ago as an abstract goal for a father-son team when the father was working in university administration and the son was just getting into the academic business. Eventually, the father returned to the laboratory, the son began to get his feet on the ground, and the goal became concrete. Now the work is finished, and our book enters the literature as, we hope, a valuable contribution to understanding the terribly complex and subtle problem of the neurobiology of motivated behaviors.We would also like the book to stand as a personal mark of a cooperative relationship between father and son. This special relationship between the authors gave us an extra dimension of pleasure in writing the book, and it would delight us if it gave anyone else an extra dimension of enjoyment from reading it. One thing we hope happens is that anyone considering a similar partnership, or simply considering entering similar fields, will take the existence of this book as encouragement. Such relationships are highly satisfying if both parties take care to protect the partnership.When we actually sat down to write the book, we were humbled by the immense literature and the smallness of both our conceived space for putting it down and of our brains for processing all the information. In some places, we consciously did not discuss a particular study or area of literature. Certainly, there are also papers we have forgotten to cite or of which we are unaware. Therefore, we invite you to write to us with your suggestions if you feel some important work or a body of literature is neglected.We would like to acknowledge the many people who helped us with Vlll Preface

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Reward summation functions are defined as the empirical functions relating running speed in a runway and waiting-box paradigm to the number or current intensity of the electrical pulses a rat receives for running. Repeated determination of such functions, with another parameter of stimulation varied between determinations, yields parameter trade-off functions. These functions describe how much of a change in one parameter is required to compensate for a change in another parameter. These functions place quantitative constraints on the neurophysiological events underlying the reward effect. Such constraints may mediate the identification of the neurophysiological substrate for the reward effect in self-stimulation.