The effect of train duration of rewarding stimulation on food self-deprivation

Abstract

In order. to assess the effect of changes in brain-stimulation reward (BSR) on food intake, train duration of BSR was manipulated during food/BSR competition periods. Train duration, rather than intensity, was used in order to hold the area of stimulation about the electrode tip constant. Train duration had a significant effect on food intake, with longer durations decreasing intake. Increases in food deprivation increased feeding during food/BSR competition, and the tendency for subjects to self-deprive was reduced over the 4 weeks of successive competition testing. Further analyses of the data revealed that stimulation on-time (defined as the product of leverpresses and train duration) was a better predictor of food intake than was leverpressing rate. The results are interpreted as supporting the hypothesis that choices for food or BSR during competition reflect the relative reward value of the alternatives.The potency of brain-stimulation reward (BSR) has been dramatically demonstrated by its ability to compete with behavior that has biologically relevant consequences (Carlisle & Snyder, 1970;Eckert & Lewis, 1967;Morgan & Mogenson, 1966;Rossi & Stutz, 1978;Routtenberg & Lindy, 1965;Spies, 1965;Stutz, Rossi, & Bowring, 1971). It has been argued that self-stimulation competes with other reinforcers by virtue of its rewarding properties (Rossi & Stutz, 1978;Stutz, Rossi, & Bowring, 1971) as opposed to its ability to reduce the competitive drive (Spies, 1965). This conclusion is based on the findings that animals who self-starve in order to obtain BSR also self-dehydrate, and that experimenter-administered brain stimulation does not significantly reduce food intake in food-deprived animals who have previously .self-starved. Further support for this position is found in research showing that the ability of BSR to compete with sweetened water is a function of the liquid's palatability (Phillips, Morgen, & Mogenson, 1971) and that food deprivation increases responses for food during BSR/food competition periods (Miliaressis & Cardo, 1973;Morgan & Mogenson, 1966 , 1972;Keesey, 1964;Ridgway, Pliskoff, & Mcintire, 1965). Increases in BSR induced by longer train durations are apparently mediated through temporal summation within a discrete population of neurons, while changes in the intensity of the stimulation modify BSR via spatial summation (Gallistel, 1973). Therefore, in order to assess the effect of changing BSR on self-deprivation with the area of stimulation held constant, train duration rather than intensity was manipulated. It was assumed that longer durations more effectively stimulate a finite population of neurons around the electrode tip whereas manipulation of intensity widens the field of stimulation. If the amount of food eaten during simultaneous access to BSR and food is an index of the comparative reward values of the reinforcers, food intake should decrease with increasing train durations. METHOD SubjectsTwenty naive male Sprague-Dawley rats (Blue Spruce Farm, Altamont, New York), weighing 350-425...

Lateral hypothalamic stimulation: Stimulus-bound eating and self-deprivation☆

“…In agreement with earlier reports [1,3] there was no critical focus within the lateral hypothalamus for evoking stimulus-bound eating. A similar conclusion may be drawn for the electrode sites of animals that were classified as "self-deprivers" as noted earlier by Rossi and Stutz [13] and Frank, Preshaw and Stutz [5]. It should be emphasized, however, that this conclusion applies only to the electrode placements within the medial to posterior extent of the lateral hypothalamus as there were no anterior hypothalamic placements and only one medial placement in our sample.…”

“…In addition to differences in the strains of rats, the two studies also differed in that baseline self-stimulation rates in the earlier study were obtained while animals were food-deprived. The earlier conclusion that magnitude of brain stimulation reward determines behavior in a competition test may ultimately prove correct [5,6,13,17]. However, in view of the shortcomings of self-stimulation rate as a measure of reward strength [7,19] and the extent of the overlap in rate scores in "deprivers" and "non-deprivers" in the present experiment, it is unlikely that even self-stimulation rates obtained under food deprivation conditions would have been correlated with food pellets eaten in the competition tests.…”

A systematic evaluation of the properties of self-stimulation train-duration response functions.

“…Notice the gradual increase in the percentage choice of the comparison duration as train duration increases. This finding is consistent with previous research, showing that longer train durations are preferred over shorter durations (Deutsch et al, 1976; Frank et al, 1982). The results seem to indicate that longer durations are more rewarding than shorter durations along the asymptotic part of the train-duration response functions.…”

“…One potential explanation for the all or nothing responses of the subjects is that once the brain stimulation reaches a reward threshold, the rats respond at near maximal rates in an attempt to keep the stimulation on continuously. This interpretation is consistent with the observation that self-stimulating rats do not respond during a stimulating train (Beyra, 1972) and that self-stimulation response rates increase as train duration is decreased (Frank et al, 1982). At the very short train durations used in Experiments 1–6, these factors lead to very rapid response rates along the asymptotic portion of the train-duration curves.…”

“…That is, does the reward value of the stimulation change from nonrewarding to maximally rewarding in a 2-4 ms trainduration interval? This seems unlikely given previous research, which indicates that reward asymptote is not achieved until train duration exceeds 1.0-s or more (Frank, Preshaw, & Stutz, 1982;Deutsch, Roll, & Wetter, 1976). However, previous studies used either discrete trial procedures or methods that ensured a no-stimulation period between successive trains.…”