The interaction of hunger and thirst in the rat

Two groups of rats were given a series of trials in an enclosed runway with a food reward at the end, one group being run hungry, the other hungry plus thirsty. Then each group was split into three sub-groups: one run hungry, the second thirsty and the other hungry plus thirsty, in each case without food reward.

It was found that, whereas on the rewarded runs the extra, “irrelevant,” thirst increased running speed, on unrewarded runs it had the opposite effect and slowed up performance. Thus on unrewarded runs the two sub-groups running thirsty, and hungry plus thirsty, ran as slowly as those running hungry. Differences were found not to depend on whether the animals had been hungry or hungry plus thirsty on previous rewarded runs.

The interaction of primary needs therefore depends on the external situation. This can be accounted for in terms of the Pavlovian theories of mutual induction and conditioning, but not in terms of Hull's theory of “irrelevant drives.”     

Incentive learning and the motivational control of instrumental performance

Hungry rats were trained to press a lever and pull a chain concurrently, with one action being reinforced with a sucrose solution and the other with food pellets. In addition, in the first two experiments all animals experienced non-contingent presentations of the two incentives in the absence of the operant manipulanda while either thirsty or hungry and either before (Experiment 1A) or after (Experiment 1B) the instrumental training. When lever pressing was assessed subsequently in extinction under thirst, the animals pressed at a relatively high rate only if (1) this action had been reinforced with the sucrose solution rather than the food pellets during training and (2) they had received the non-contingent presentations of the sucrose solution and food pellets on days on which they were thirsty rather than hungry. A third experiment demonstrated that non-contingent exposure to the sucrose solution alone, but not to water under thirst was sufficient to bring about this type of motivational control of instrumental performance.     

Motivational control of instrumental performance following a shift from thirst to hunger

Thirsty rats were trained to press a lever for either a sucrose solution or saline before performance was tested in extinction while the animals were either hungry alone or experiencing both hunger and a sodium appetite. Reinforcer-specific motivational control was observed in that the animals trained with the sucrose solution pressed more than those trained with the saline when they were tested hungry, but not when they were tested under combined hunger and sodium appetite. In order to assess the role of a Pavlovian incentive process in this effect, thirsty animals received non-contingent pairings of one stimulus with the sucrose solution and another with saline in the second experiment. In an extinction test the sucrose stimulus augmented lever pressing relative to the saline stimulus when the animals were hungry, but not when they were thirsty. In the subsequent experiments the contribution of the Pavlovian process was equated by giving concurrent training with both incentives. Lever pressing and chain pulling were reinforced concurrently, one with the sucrose solution and the other with saline, while the animals were thirsty. Once again, the animals pressed more in extinction if this action had been trained with the sucrose solution rather than the saline, but only if they were hungry rather than thirsty. Thus, instrumental performance across a thirst-to-hunger shift can also be controlled by an instrumental incentive process. The direct engagement of the instrumental process by this motivational shift contrasts to the absence of such control following a hunger-to-thirst transition (Dickinson & Dawson, 1987a), a fact attributed to the asymmetrical motivational interactions produced by water and food deprivation.     

Motivational control of blocking

Hungry and thirsty rats lever pressed for food pellets in 1 visual stimulus (V1) and for a saline solution in another stimulus (V2). In a 2nd phase, the rats were made either hungry or thirsty and pressed for a starch solution in 2 stimulus compounds, each containing 1 of the visual cues and an auditory cue, that is, V1A1 and V2A2. On test, rats responded less to A1 than to A2 when hungry but less to A2 than to A1 when thirsty. Two further experiments replicated this selective blocking effect when the rats were both hungry and thirsty during Phase 2 and demonstrated that the magnitude of blocking was comparable to that observed when the reinforcer identity was held constant across the 2 phases.     

Transfer across drives of the discriminative effect of a Pavlovian conditioned stimulus

Previous results suggest that a stimulus paired in Pavlovian fashion with reward should exert some discriminative control over an unrelated operant response acquired under a different drive-reward system. In the following experiment, a stimulus was first paired with food reinforcement for a hungry rat. Subsequently, the animal learned to lever-press for water reinforcements when thirsty but not hungry. Finally, the control over lever-pressing of the food-paired stimulus was tested by presenting it at various times during extinction of the lever-pressing response. All animals in the experiment showed the expected effect; each emitted more lever-presses during periods of the food-paired stimulus than during alternate control periods.     

The addition of saccharin to taste cues affects taste preference conditioning in thirsty rats

Previous failures to condition preferences for the unacceptable taste cues sucrose octaacetate (SOA) and citric acid (CA) using a reverse-order, differential conditioning procedure (Forestell & LoLordo, 2000) may have been the result of low consumption of the taste cues in training or of their relatively low acceptability to rats that are thirsty and hungry. In the present study, rats that were thirsty but not hungry readily consumed the SOA and CA conditioned stimulus solutions in training. In test, stronger preferences were displayed for CS+ if the taste cues had been mixed in water (i.e., for the previously unacceptable taste cues) than if they had been made more acceptable by the addition of saccharin in training and test. In Experiment 2, again with rats that were thirsty but not hungry, stronger preferences for CS+ were observed when taste cues were presented in water in the test than when they were presented in saccharin. Addition of saccharin to the taste cues in test eliminated the preference for CS+.     

The Hull-Leeper drive discrimination situation-a control experiment

An experiment was conducted testing the author's explanation of the discrepancy between results obtained by Hull and Leeper in a similar situation. Animals were run either hungry or thirsty to obtain the appropriate reward by making one response when hungry and another when thirsty. For all groups the reward was in the same goal-box. The first group (Leeper) had the goal-box divided with each side being accessible only if the animal had made the correct response initially. The second group (Hull) had the same goal-box for both rewards, but if the wrong path was taken the animal was prevented from reaching the goal by a block. The third group had the same goal-box for both rewards again, but the animal could reach the goal-box even if the wrong path was taken and discovered the unwanted reward in the goal-box. The results confirm the predictions made from the author's theory.     

Learning about water by hungry rats

In Experiments 1 and 2 hungry rats were trained in a straight alley with consistent food reward (FF), food and nonreward trials intermixed (FN), or food and water trials intermixed (FW). In Experiment 1 rats were tested with nonrewarded trials (extinction) and Groups FN and FW did not differ, both running faster then Group FF. In Experiment 2 rats were tested with consistent water reward, and Group FW ran faster then Group FN, which was superior to Group FF. In Experiment 3, one group of hungry rats was trained on a single alternating schedule of food and water in Phase 1 and was shifted to a single alternating schedule of food and nonreward in Phase 2 (Group FW); the second group (Group FN) received a single alternating schedule of food and nonreward in both phases. When Group FW was shifted to nonreward from water, performance to nonreward was temporarily disrupted. These results indicate that, contrary to previous conclusions, hungry rats can learn about water when drive is strong and food is received in the situation.     

Incentive learning following reinforcer devaluation is not conditional upon the motivational state during re-exposure

Three experiments analysed the effect of re-exposure to the reinforcer following aversion conditioning on instrumental performance. In the first experiment, groups of hungry and thirsty rats were trained to press a lever for sucrose, which was then followed by a single injection of lithium chloride (LiCl). On the following day, half the animals in each motivational condition received re-exposure to the sucrose solution; the remaining animals were not re-exposed. In a subsequent extinction test animals that had received re-exposure to the sucrose pressed less than animals that were not re-exposed. Moreover, the effect of re-exposure to the sucrose solution was similar following training under hunger and thirst. In the remaining studies, animals were trained to lever-press for sucrose while either hungry or thirsty. They were then injected with LiCl and re-exposed to the sucrose while either hungry or thirsty, i.e. in the same or different motivational state employed during training, or they were not re-exposed. Lever pressing was then tested in extinction in the training motivational state. As in the first experiment, re-exposure to the reinforcer after aversion conditioning enhanced the magnitude of the reinforcer devaluation effect. More importantly, re-exposure to the sucrose produced a comparable effect on instrumental performance, whether re-exposure was given under the same or different motivational state to that employed during training. These results suggest that the instrumental reinforcer devaluation effect depends upon a process of incentive learning, but that this process is not conditional upon the current motivational state of the animal.     

Incentive properties of sucrose and saccharin under different deprivation conditions

In Expt 1 it was found that hungry rats developed a 100% preference for 8% sucrose over water in a maze-choice situation, whereas thirsty rats developed no preference. When deprivation conditions for the two groups were reversed the pattern of preference relations also reversed. In a 2nd experiment nondeprived rats developed a preference for either 8% sucrose or 0.2% saccharin over water while thirsty Ss did not develop a preference for either of these over water. The results are discussed in terms of incentive theory.     

Time-shared feeding and drinking

Barbary doves were tested in an operant situation in which they characteristically alternate between feeding and drinking. The experimental findings may be summarized as follows: (1) the cumulative distribution of the intervals between feeding bouts is little affected by reward rates; (2) a lock-on index is correlated with reward rate, but is not affected by altering reward rate per se, as long as the overall rate of ingestion remains the same; (3) when a primarily hungry animal is interrupted while feeding, or a primarily thirsty animal while drinking, the behaviour is resumed after the interruption; (4) when a primarily hungry animal is interrupted while drinking, or a primarily thirsty animal while feeding, the behaviour is resumed after a short interruption, but changes to the alternative behaviour following a long interruption; (5) titration of interruption period in the dominant region of the motivational state space is always stable, but becomes unstable if the dominance changes, or if the titrating criteria are reversed. From this evidence it is concluded that feeding and drinking can be time-shared in a manner analogous to that found in computers.     

Learned preference for a hedonically negative flavor is observed after pairings with positive post-ingestion consequences rather than with a palatable flavor

In two experiments, thirsty rats consumed a compound of sucrose and a non-preferred flavor. In Experiment 1, a conditioned preference was observed in the experimental group when animals were tested both thirsty and hungry, but not when they were tested just thirsty. Animals in the control group, which experienced the flavor and the sucrose unpaired, never showed a preference. Experiment 2 replicated the absence of a preference in the experimental group when rats were tested thirsty, but provided evidence that a flavor-taste association had been formed during training. After conditioning, sucrose was paired with LiCl in group Dev whereas it was unpaired in group NonDev. The sucrose devaluation produced a decrease in CS preference in group Dev, and an increment in group NonDev. Taken together, these results show that preference for a non-preferred flavor can be readily observed after pairings with the positive consequences of the US (calories or absence of an expected illness) rather than with a palatable flavor.     

Putting behavior on hold decreases reward value of need-instrumental objects outside of awareness

We examined whether cues that put impulsive behavior towards rewarding objects on hold reduces the value of the rewarding objects outside of conscious awareness. We manipulated the reward value of water by making participants thirsty, or not. Next, a bottle of water was subliminally presented in a go/no-go task, and paired with either go cues or no-go cues (putting behavior on hold). Subsequently, as a measure of reward value of water, participants estimated the size of water objects. Results showed that repeatedly withholding behavior towards water reduced the perceived size of water objects, but only when participants were made thirsty. These results suggest that withholding impulsive behavior towards objects that serve basic needs nonconsciously reduces reward value of these objects. Implications for nonconscious behavior regulation are briefly discussed.     

Are schedule-induced drinking and displacement activities causally related?

The acquisition of schedule-induced drinking was studied in hungry rats given food according to an intermittent (fixed-time 45-s) schedule, in three separate experiments. Rate of acquisition of induced drinking was not affected by making the rats thirsty as well as hungry (Experiment I), nor by offering them a palatable saline solution instead of water (Experiment II). Thirst and palatability did affect the asymptotic level of induced drinking. Increasing the level of food deprivation (Experiment III) increased both the rate of acquisition of induced drinking and its asymptotic level. Thus, rate of acquisition of induced drinking was found to depend more on causal factors relevant to feeding than on causal factors relevant to drinking, while asymptotic level of drinking was affected by both types of causal factor. This suggests that the occurrence of induced drinking does not depend primarily on a disinhibition mechanism of the type thought to underlie displacement activities, and hence does not support the idea that induced drinking is a type of displacement activity.     

Water can induce better spatial memory performance than food in radial maze learning by rats1

Abstract: Two experiments were carried out to test the differential effects of hunger and thirst on memory performance. In Experiment 1, two groups of rats were exposed to an original radial‐maze task and then to a 30‐min retention‐memory task. The food‐deprived group completed the original task more quickly than the water‐deprived group, but the thirsty group mastered the memory task more quickly than the hungry group (p < 0.01). In Experiment 2, deprivation conditions were changed from the original to the memory task. The food‐water group completed the memory task more rapidly than the water‐food group (p < 0.05). Thirst proved to constitute a more favorable condition for retention‐memory learning. The applicability of several theories is discussed.     

The role of exploration in win-shift and win-stay performance on a radial maze

Win-shift spatial memory tasks in a radial maze reinforce animals for avoiding previously visited rewarded arms; win-stay tasks reinforce them for returning to those arms. Win-shift tasks have generally been found much easier to perform, and this may be explained either in terms of foraging models which postulate avoidance of locations where food has been found, or in terms of the predominance of spontaneous alternation (exploration). Experiment 1 examined spontaneous alternation behavior in the radial maze as a function of whether the first visit to an arm had been rewarded or not, and showed that alternation was more probable after nonreward than after reward in both hungry and thirsty rats (a result which conflicts with the foraging account of the win-shift superiority). Experiment 2 replicated the finding that win-stay discrimination performance was inferior to win-shift. A manipulation (lengthening the delay between initial and test choices) which weakens spontaneous alternation, reduced, but did not reverse, the win-shift superiority. In Experiment 3, in order to eliminate the influence of spontaneous alternation, versions of the win-stay and win-shift tasks were devised in which, unlike the original task, all arms were familiar at the choice trial. Under those conditions win-stay was performed better than win-shift. It is concluded that spontaneous alternation plays a major role in many spatial memory tasks, and that the results can best be accounted for by combining principles of exploration and simple associative learning, without recourse to foraging models.     

The effect of hunger on water intake in rats

Although reciprocal inhibition between eating and drinking has been postulated, the commonly observed reduction of water intake by hungry rats may not be due to any direct inhibitory mechanism. In one experiment rats deprived of food for 24 hr. and then injected with 2 ml. of NaCl drank the same as rats that had received food ad lib. In the second experiment a stomach load of 10 ml. of water 3 hr. before the salt injection was designed to abolish any water deficit that might have occurred during food deprivation had there been inhibition of drinking by hunger. Here again rats deprived of food did not drink less than undeprived animals. In fact the hungry rats drank slightly but significantly more. This phenomenon may be related to the observation confirmed here that during food deprivation rats excrete about twice as much rather dilute urine as during ad lib food intake. This seems to indicate that though in general food deprived rats drink less than normal they actually drink more than they need. Schedule induced polydipsia also occurs during food deprivation and this too makes it unlikely that water-intake is actually inhibited during hunger.     

进化观点下的幸福研究

人类社会生活的一项重要目标是追求幸福(happiness), 影响幸福体验的因素有食物、财富、婚姻及友谊等。寻求幸福与避免痛苦能让人们的幸福需求得到满足。幸福和痛苦不是人类通过进化获得的一种最终机能, 然而幸福和痛苦对人类远古祖先的影响在于调节行为活动以增加生存与繁衍可能。为什么有些环境刺激比其他刺激更能让人体验幸福？为什么回避痛苦与追求幸福同样重要？为什么幸福体验有相对性、过度性与目标性的特点？这些问题可以在进化观点中得到较好回答。人们的幸福感可以在认识基因与环境关系的基础上得到加强, 如加强亲属联系、强化社会合作、重视婚姻承诺以及满足本能欲望等。     

Predicting Hunger: The Effects of Appetite and Delay on Choice

Preferences often fluctuate as a result of transient changes in hunger and other visceral states. When current decisions have delayed consequences, the preferences that should be relevant are those that will prevail when the consequences occur. However, consistent with the notion of an intrapersonal empathy gap (Loewenstein, 1996) we find that an individual's current state of appetite has a significant effect on choices that apply to the future. Participants in our study made advance choices between healthy and unhealthy snacks (i.e., fruit and junk food) that they would receive in 1 week when they were either hungry (late in the afternoon) or satisfied (immediately after lunch). In 1 week, at the appointed time, they made an immediate choice, an opportunity to change their advance choice. Our main predictions were strongly confirmed. First, advance choices were influenced by current hunger as well as future hunger: hungry participants chose more unhealthy snacks than did satisfied ones. Second, participants were dynamically inconsistent: they chose far more unhealthy snacks for immediate choice than for advance choice. An additional hypothesis related to gender differences was also confirmed.     

Motivational control of instrumental performance: The role of prior experience of the reinforcer

In four experiments we investigated the conditions that are necessary for instrumental performance to adjust appropriately to a change in drive state. Rats were trained to press a lever and pull a chain concurrently, with one action being reinforced by sucrose solution and the other by food pellets. In Experiment 1 for animals that were hungry throughout training the rate of lever pressing in an extinction test under thirst was unaffected by the type of reinforcer produced by this action during training, even though the sucrose solution would maintain a higher rate than the food pellets during training under thirst. In contrast, animals that experienced the instrumental contingencies arranged by the concurrent schedule while thirsty at some point during training pressed the lever more during the extinction test under thirst when this action had been reinforced with the sucrose solution rather than the food pellets. The remaining three experiments demonstrated that for this incentive effect to occur it is sufficient that the sucrose solution be delivered non-contingently under thirst at some stage of training. Thus, it would appear that performance mediated by an instrumental contingency adjusts appropriately to reinforcer revaluation brought about by a drive shift only if the animals have had prior experience with the incentive under the test drive state. This observation was interpreted in terms of Tolman's “cathexis” theory of motivation.