Temporal integration in self-stimulation: A paradox

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Investigated temporal summation of the rewarding effects of medial forebrain stimulation in 4 male Sprague-Dawley rats by varying the interval separating the 2 short bursts of stimulation given as a reward in a runway. One finding of Exp I–that the reinforcing effect of the 2 bursts was 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, Exp II (with the Ss from Exp I) showed that charge-duration functions obtained with different levels of performance differed by a multiplicative (scalar) factor–that is, the ratio between the values of the 2 functions was everywhere the same. The models of postsynaptic integration are not capable of explaining simultaneously the fact (a) that the strength-duration function is a perfect hyperbola that has nearly reached its rheobase at a train duration no greater than 2 sec; (b) that there is no detectable effect of interburst interval on summation between bursts separated by intervals up to 2 sec and longer; and (c) that the strength-duration functions (or, equivalently, the charge-duration functions) derived by using different performance criteria differ by a multiplicative factor. (15 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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