- Published 1984 in Behavioral neuroscience

Temporal summation of the rewarding effects of medial forebrain stimulation in the rat was investigated by varying the interval separating the two short bursts of stimulation given as a reward in a runway. One finding--that the reinforcing effect of the two bursts is independent of interburst interval--supports a model in which there is perfect summation of the portion of the reward signal that exceeds some threshold. However, the constant-threshold form of this model is not reconcilable with the results of a second experiment, which shows that charge-duration functions obtained with different levels of performance differ by a multiplicative (scalar) factor, that is, the ratio between the values of the two functions is everywhere the same. (The charge-duration function gives the charge required as a function of the train duration.) None of the models of postsynaptic integration so far suggested is capable of explaining simultaneously the fact that the strength-duration function is a perfect hyperbola that has nearly reached its rheobase at a train duration no greater than 2 s, that there is no statistically detectable effect of interburst interval on summation between bursts separated by intervals up to 2 s and longer, and that the strength-duration functions (or, equivalently, the charge-duration functions) derived by using different performance criteria differ by a multiplicative factor.

@article{Sax1984TemporalII,
title={Temporal integration in self-stimulation: a paradox.},
author={L D Sax and Charles R. Gallistel},
journal={Behavioral neuroscience},
year={1984},
volume={98 3},
pages={467-8}
}