Investigating the devaluation explanation for negative anticipatory contrast.

This study addressed whether negative anticipatory contrast results in a decrease in the value of the low-valued substance. Rats responded in training conditions designed to produce negative contrast. They then responded in test sessions in which the low-valued substance from the training sessions was the reinforcer for an operant response. Despite the finding of contrast in the training conditions, the low-valued substance was a more effective reinforcer early in testing after training conditions in which it had been followed by access to the high-valued substance than after training conditions in which it had not. The findings question the devaluation explanation for contrast but may be similar to other findings of reversals of "preference." (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Investigation of the devaluation interpretation of anticipatory negative contrast.

12 male Sprague-Dawley rats suppress intake of an acceptable substance (saccharin and sucrose) when it is followed by a preferred substance. Learned devaluation of the initial solution in suppressed intake was investigated. Findings included: Flavors or odors as within-subject cues precluded the occurrence of anticipatory contrast, conditioning flavor and odor preferences instead, which appeared to antagonize suppressed intake; Anticipatory contrast was obtained when within-subject context cues, temporal alternation cues, or drinking-spout cues were used; Preference tests conducted with the spout cues showed that devaluation of the initial substance was not necessary for the occurrence of negative anticipatory contrast. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Within-subjects positive and negative contrast effects in rats.

Conducted 4 experiments, using a total of 47 Sprague-Dawley albino rats. Ss were given alternating 1-min access periods to 2 tubes containing either 32 or 4% sucrose solutions for daily 6-min test sessions. Lick rate for 32% was higher under comparison (32 vs 4) than noncomparison (32 vs 32) conditions; and lick rate for 4% was lower under comparison conditions (4 vs 32) than under noncomparison conditions (4 vs 4). All sucrose conditions were varied within Ss, and both positive and negative contrast were obtained with a small n. In addition to lick rate, intake and latency measures revealed contrast effects. Deprivation conditions altered latency but not lick rate measures of contrast. Reducing the test session to 3 min (alternating 30-sec access periods) did not greatly affect contrast. Additional experiments provided evidence for distinct within- and between-days contrast effects, as well as a between-groups contrast effect. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the pontine parabrachial nuclei eliminate successive negative contrast effects in rats.

Rats shifted from a high to a low concentration of sucrose make fewer licks for the low concentration than rats that experience only the low concentration of sucrose. This phenomenon, referred to as successive negative contrast, is eliminated after bilateral electrolytic lesions of the amygdala. Because the amygdala receives direct projections from the gustatory zone of the parabrachial nuclei of the pons (PBN), this experiment was designed to examine this phenomenon in 43 male rats with electrophysiologically guided bilateral electrolytic lesions of the PBN. The results of this experiment showed that lesions of the PBN fully prevent contrast in rats shifted from the high to the low concentration of sucrose. Thus, an intact PBN is essential for the occurrence of successive negative contrast effects in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of varied preshift reward magnitude on successive negative contrast effects in rats.

A total of 110 male Sprague-Dawley albino rats, distributed across 3 experiments, received simple instrumental conditioning trials in a straight runway. In each experiment the conditions of reward prior to a shift to small reward were varied between groups. Collectively, results indicate that the extent of the negative contrast effect depends upon the difference between pre- and postshift incentive levels and that Ss exposed to varied reward magnitude training average the incentive values of these rewards. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory thalamus lesions eliminate successive negative contrast in rats.

Neurologically intact rats expecting to receive a high-value reward (1.0 M sucrose), licked less for an unexpected low-value reward (0.15% saccharin) than did control subjects that only received the saccharin solution. This reward comparison effect, termed successive negative contrast, was eliminated after bilateral electrolytic lesions of the gustatory thalamus. The results are discussed in terms of disrupted memory processes that may have rendered the lesioned rats incapable of computing the relative reward value of the available solution (0. 15% saccharin) with respect to the memory of the preferred solution (1.0 M sucrose). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

From contrast to reinforcement: Role of response contingency in anticipatory contrast.

Intake of a 0.15% saccharin solution is suppressed if access to the saccharin is followed by access to 32% sucrose in brief daily pairings. The present series of four experiments was concerned with factors that lead to this anticipatory contrast effect (suppressed saccharin intake) rather than a reinforcement effect. In Experiment 1, anticipatory contrast was obtained with an autoshaping procedure (no lick requirement on the initial tube), and degree of contrast did not vary as a function of intersolution interval in the range of 0–25 s. Experiments 2 and 3 showed that requirements of 10, 100, 200, or 400 licks on the first tube available led to a reinforcement effect in latency, but a requirement of 0 licks (autoshaping procedure) led to a contrast effect in licks and latency. In Experiment 4, a group with a 200-contingent-lick requirement showed a reinforcement effect in latency, but a group yoked to this contingent group showed a contrast effect in both latency and licks. Overall, the results suggest that anticipatory contrast occurs under conditions of a "relaxed" instrumental contingency. The data are discussed in terms of control of behavior by stimulus–stimulus, response–stimulus, and stimulus–response associations, and the results are related to behavioral contrast, to flavor–outcome associations, and to "misbehavior" produced by Pavlovian-instrumental interactions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of successive negative contrast and its dissociation from other paradoxical reward effects in preweanling rats.

Studied the effects of abrupt reductions in reward magnitude (the successive negative contrast—SNC—effect) in Sprague-Dawley rats of various ages and with dry pellet or milk rewards. In Exp I, SNC was shown in 61–68 day olds but not in 17–24 day olds with food reward. Exp II showed strong SNC at 34–35 days and marginal contrast at 25–26 days, again with food reward. With milk reward (Exp III), there was a clear SNC effect at 25–26 days, a slight effect at 20–21 days, but no effect in 16–27 day olds. Results suggest that SNC occurred earlier with milk than with dry food reward. Exp IV repeated the 16–27 day milk-reward condition of Exp III with more highly massed trials. Reduction of reward size reduced performance to the level of an appropriate small-reward control. Finally, Exp V demonstrated a dissociation of SNC and other paradoxical reward effect at 16–27 days of age. The extinction effects of partial reinforcement (PREE), partial delay of reinforcement, and varied magnitude of reward were large and clear. These results are related to earlier work on the ontogeny of SNC in even younger animals and are discussed in relation to an apparent transitional period of the PREE in ontogeny. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential conditioning and contrast effects in rats.

Considers previous research, using a differential conditioning procedure to examine contrast effects in the runway, inadequate due to the operation of a ceiling effect and/or a decision-time problem. A special procedure (delay of reward and massing trials) was used to solve these problems in an experiment with 40 male Holtzman albino rats. Results reveal reliable positive and negative contrast effects. Data support the conclusions, that (a) it is reasonable to seek a common explanation of behavioral contrast (operant) and incentive contrast (runway) data; (b) perceptual theories of contrast, predicting both positive and negative contrast, are to be preferred over theories designed to predict only negative contrast; and (c) the type of response, and extraneous variables which affect it, needs to be carefully considered in dealing with reward manipulations. (21 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decremental effects of context exposure following delay eyeblink conditioning in rabbits.

The conditioning context arises from the relatively static features of the training environment. In rabbit eyeblink conditioning, procedures that retard acquisition (conditioned stimulus [CS] preexposure, unconditioned stimulus preexposure, blocking manipulations) are attenuated by context changes. In this article the authors investigate the effect of context exposure after initial delay conditioning. After conditioned responses (CRs) were established, one group received 6 sessions of context exposure, whereas control groups either remained in their home cages or received exposure to handling and a novel context. Thereafter, all groups received CS-alone testing. The expression of CRs was substantially reduced following context exposure relative to any retention loss in the home-cage control. Exposure to handling and a novel context facilitated the CRs rather than reducing them. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age of first appearance of simultaneous and successive negative contrast in infant rats.

Simultaneous (SimNC) and successive (SNC) negative contrast, 2 paradoxical effects that are related to shifts in reward magnitude, were studied in 148 rat pups. In Exps I and II, 11-, 14-, and 17-day-old Ss were able to discriminate between the large (milk suckling) and small (dry suckling) reward odor cues as measured by attachment latencies, but only the 14- and 17-day-olds showed SimNC. At none of the 3 ages was a discrimination formed to the differential odor cues in the alley in terms of runway speeds. In Exp III, Ss were placed directly on the dam's ventrum to facilitate attachment. As in the earlier experiment, the 11-day-olds discriminated between the odors signaling the 2 reward conditions but did not show the SimNC effect. In Exp IV, SNC was shown at 17 days but not at 14 days in the attachment latency measure and at neither age in the run measure. These 4 experiments extend earlier findings that the paradoxical effects that emerge out of intermittent schedules of reward magnitude occur earlier than those associated with single abrupt shifts in reward magnitude. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Successive, simultaneous, and anticipatory contrast in the consumption of saccharin solutions.

Contrast effects were obtained in 234 male Sprague-Dawley rats in the consumption of saccharin solutions in 3 paradigms. Results show that degree of negative contrast varied as a function of concentration disparity, but not equally in the 3 procedures. Successive negative contrast occurred following shifts from 0.15% to either 0.075 or 0.05% saccharin but did not occur following shifts to 0.10 or 0.125% saccharin. Some degree of simultaneous contrast was obtained with all 4 concentration disparities. Anticipatory contrast, where the intake of the 1st substance is suppressed by a more preferred 2nd substance, occurred only in the case of 0.05–0.15% differences in concentrations. It was suggested that the several contrast paradigms engage somewhat different psychological processes differentially involving emotional, sensory, and associative mechanisms, but all lead to behavior based on relative value. A modification of F. M. Toates's (1981) incentive model of ingestive behavior was suggested to incorporate relativity effects based on both associative and nonassociative factors in the consumption of both nutritive and nonnutritive substances. (69 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the pedunculopontine tegmental nucleus increase sucrose consumption but do not affect discrimination or contrast effects.

Pedunculopontine tegmental nucleus (PPTg) lesions block place preferences to drugs or food only when animals are nondeprived. PPTg lesions also disrupt operant responding, but lesioned rats cannot discriminate active from inactive levers. It is not clear, therefore, whether PPTg lesions block reward or disrupt the ability to differentiate changes in reward magnitude. These hypotheses were tested by measuring sucrose consumption, choice, and contrast effects after PPTg lesions. Both sham and lesioned rats consumed greater amounts of a sucrose solution as the concentration and level of deprivation were increased. Given a choice between 2 solutions, all rats consumed more of the higher concentration. Both groups exhibited contrast effects when the concentration was shifted from 32% to 4% within a session. Somewhat surprisingly, lesions increased sucrose intake when rats were food-restricted. These results suggest that PPTg lesions do not disrupt primary motivation or the ability to evaluate and respond to changes in reward strength. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory thalamus lesions eliminate successive negative contrast in rats: Evidence against a memory deficit.

Successive negative contrast is the exaggerated reduction of licking that occurs when rats expecting a high-value reward are given a low-value reward. This effect is typically investigated with a 24-hr retention interval between access periods. The present experiment tested the hypothesis that the absence of successive negative contrast in rats with bilateral lesions of the gustatory thalamus (GT) is due to a memory deficit. The results argue against this hypothesis by showing that, irrespective of retention-interval duration (7.5 min, 15 min, 45 min, 180 min, or 24 hr), lesioned rats failed to show successive negative contrast. As such, the data are consistent with the alternative view that GT lesions specifically disrupt the reward comparison mechanism that underlies successive negative contrast. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Insular cortex and consummatory successive negative contrast in the rat.

Rats that are expecting a high value reward (e.g., 1.0 M sucrose) show an exaggerated underresponding when they are instead given a low value reward (e.g., 0.15% saccharin), an effect termed successive negative contrast (SNC). In the present experiment, insular cortex-lesioned (ICX) rats showed normal responsivity to sucrose and saccharin prior to the reward downshift. However, when switched from sucrose to saccharin during the postshift trials these rats displayed no evidence of SNC. Indeed, over the downshift trials these ICX rats consistently drank more saccharin than the ICX rats maintained on saccharin throughout the experiment. Potential interpretations are discussed including a lesion-induced impairment in the ability to accurately recognize the novelty of the postshift saccharin stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective breeding for negative contrast in consummatory behavior.

Rats showing either large or small reductions in licking following a shift from 32% to 4% sucrose were selectively bred for 7 generations. Rats from the 2 resulting lines reliably differed in successive negative contrast and in activity (radial-arm maze and open field). Differences in activity and contrast were not correlated. Heritability (h–2) of the reaction to sucrose shift was reliable in the last 6 filial generations and equaled 0.64 in the F? generation. The 2 lines did not differ (1) in response to the absolute rewarding value of sucrose or cocaine; (2) in open-field defecations or thigmotaxis; (3) in anticipatory contrast; or (4) in responsivity to midazolam. Responsivity to reward reduction may involve a relatively delimited psychological process that is amenable to selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Suckling and sucrose ingestion suppress persistent hyperalgesia and spinal Fos expression after forepaw inflammation in infant rats

The native TRH receptor (TRH-R), which is a G protein-coupled receptor that signals via the phosphoinositide transduction pathway, has been assumed to be inactive in the absence of agonist. In contrast, a mutant mouse TRH-R (C335Stop TRH-R) was shown previously to exhibit constitutive (or agonist-independent) signaling activity. In this report, we measured signaling activity of TRH-Rs using a protein kinase C-responsive reporter gene instead of formation of inositol phosphate second messenger molecules. Using this more sensitive system, we show that native mouse TRH-Rs exhibit agonist-independent signaling activity that is directly proportional to the number of receptors expressed in COS-1 cells and is inhibited by negative antagonist benzodiazepine drugs. As expected, the basal signaling activity of native TRH-Rs is lower than C335Stop TRH-Rs. Constitutive activity of native TRH-Rs is not peculiar to COS-1 cells in which receptor density is markedly elevated, because it can also be demonstrated in Madin Darby canine kidney cells stably expressing mouse TRH-Rs and GH4C1 cells endogenously expressing rat TRH-Rs. These findings support the thesis that native TRH-Rs oscillate between active and inactive states. We suggest that demonstration of constitutive activity of native receptors may depend on the sensitivity of the signaling assay employed.     

Differential effects of postingestive feedback on the reward value of sucrose and lateral hypothalamic stimulation in rats.

The effects of postingestive feedback on the value of intraoral sucrose and lateral hypothalamic (LH) stimulation were compared. Rats chose between a fixed LH stimulation train or a compound reward composed of the same stimulation train and an oral infusion of 1 M sucrose. The rats preferred the compound reward when postingestive feedback was reduced by opening a gastric cannula. However, when the cannula was closed, the compound was preferred only at the beginning of each session, and preference declined or reversed as consumption continued. A 2nd experiment showed that the reduction in preference caused by closing the gastric cannula was not due to a punishing effect of the gastrointestinal load. This study suggests that postingestive signals modulate gustatory reward at a stage of processing before gustatory and brain stimulation rewards are combined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some determinants of milk ingestion in suckling rats.

Eight experiments were conducted to examine several possible determinants and controls of milk intake in 10-day-old preweanling Sprague-Dawley rats. Results indicate that while the amount of milk the mother provides is a major determinant of milk consumption, pups will individually adjust their intake in response to certain treatments. Deprived pups ingested more milk than nondeprived littermate controls if given access to enough milk. Intragastric intubations of skimmed milk or distilled water reduced milk intake; heavy cream or isotonic saline did not. Injections of polyethylene glycol or formalin, which produced hypovolemia, increased milk consumption, and hypertonic saline decreased it. Results indicate that preweanling rats are behaviorally responsive to certain changes in body fluids and suggest that milk intake involves more than an invariant reflex. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Additivity of taste-specific effects of sucrose and quinine: Microstructural analysis of ingestive behavior in rats.

Effects of sweet and bitter tastes on ingestion were studied by timing licking responses. 12 water-deprived rats were given 15-min access to sucrose (SU) solutions (0.00, 1.25, 2.50, and 5.00%) with and without quinine (Q; 0.01%) and to Q solutions (0.00, 0.0025, 0.005, and 0.01%) with and without SU (5.00%). Volume ingested and number of licks increased with SU and decreased with Q. In response to SU, the number of bursts increased, and interlick intervals lengthened. In response to Q, licks to ingest 1 ml of solution, burst number, and percentage of slow licks increased, and burst size decreased. When Q and SU were mixed in the same solution, the pattern of ingestive responses manifested attributes of both tastes. Results suggest 2 separate, parallel systems that operate simultaneously to govern rats' licking behavior. One system expresses the effects of SU on the pattern of ingestion and the other expresses the effects of Q. (PsycINFO Database Record (c) 2010 APA, all rights reserved)