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)     

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)     

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)     

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 in the rat: II. Aversive and appetitive taste conditioning.

The learning capacities of rats with electrolytic lesions of the gustatory thalamus (GT) were investigated in 3 experiments. In Experiment 1, the presence of a taste cue failed to overshadow odor aversion learning in the lesioned rats, yet these same animals acquired normal taste and odor aversions. Thalamic lesions had no discernible effect on the acquisition of a conditioned flavor preference in Experiment 2. Finally, GT lesions completely reversed the anticipatory contrast effect shown by control subjects in Experiment 3. These results suggest that damage to the GT spares taste detection and recognition and simple associative learning but interferes with learning that involves more complex gustatory information processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory thalamus lesions in tbe rat: I. Innate taste preferences and aversions.

Two experiments examined the innate taste preferences and aversions of rats with electrolytic lesions of the gustatory thalamus (GT). Contrary to previous research, GT lesions had only a minor influence on intake of the 4 basic-tastes as assessed with the 24-hr, 2-bottle preference test in Experiment 1. The same lesioned rats, when tested with the same stimuli in the 15-min, single-bottle procedure in Experiment 2, showed normal consumption patterns except for sucrose intake, which was attenuated. The conflicting findings of previous and present research are considered to result from differences in lesion size. The current data suggest that the GT has a relatively minor functional role in the unconditioned acceptance or rejection of sapid stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory parabrachial lesions disrupt taste-guided quinine responsiveness in rats.

This study examined the effects of electrophysiologically placed electrolytic lesions in the gustatory zone of the parabrachial nuclei (PBN) on the rat's taste-guided unconditioned licking of quinine hydrochloride during repeated 10-sec trials. Concentration–response functions measured in water-deprived rats before and after surgery significantly shifted to the right as a result of the bilaterally placed lesions. These same rats were tested on their ability to acquire a lithium chloride (LiCl)-based conditioned taste aversion (CTA) to 0.1 M sucrose. Although the largest lesions severely affected performance in both tasks, there was only a modest correlation (r?=?–.447) between the extent of the lesion-induced shift in the quinine concentration–response curves and the degree of sucrose intake suppression after the first CTA conditioning trial. Thus, PBN lesions can disrupt performance on both tasks, but it appears that the neural processes governing unconditioned responsiveness to quinine may be to some extent dissociable from those subserving acquisition of a sucrose–LiCl-based CTA. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory detection thresholds after parabrachial nuclei lesions in rats.

Rats with either electrolytic (Experiment 1) or excitotoxic lesions (Experiment 2) that had been electrophysiologically centered in the gustatory zone of the parabrachial nuclei (PBN) were tested for sucrose and NaCl taste detection thresholds in a conditioned avoidance task. With 1 exception, all of these rats had previously shown severe deficits in acquiring an LiCl-based conditioned taste aversion (CTA) to sucrose, NaCl, or alanine. The rats with excitotoxic lesions also had failed to express a depletion-induced sodium appetite. Despite the uniformity of these deficits, the rats with lesions exhibited varied performance in the detectability task. Roughly ? of the rats did not perform competently, ? had elevated thresholds, and ? showed no or only marginal impairments in taste detectability. These findings demonstrate that the elimination of CTA following PBN lesions is not necessarily linked to an impairment in taste signal detection. Thus, PBN-induced deficits on 1 taste-related task do not entirely correspond with impairments on another. (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)     

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)     

Progressive ratio performance in rats with gustatory thalamus lesions.

To determine whether damage of the gustatory thalamus (the parvicellular region of the ventroposteromedial nucleus) disrupts the perceived value of reinforcing stimuli, the performance of rats with bilateral, electrophysiologically guided, electrolytic lesions of the area was examined in Experiment 1 with a progressive-ratio schedule of reinforcement. Lesioned rats showed normal concentration-dependent changes in break point (an index of the amount of effort a subject will expend to obtain reinforcement) and in consummatory responding (licking) for the sucrose reward. In the reward comparison procedure of Experiment 2, however, the same lesioned rats failed to show morphine-induced suppression of alanine consumption. The results provide no support for the view that the thalamic taste area is involved in the perception of the absolute reinforcing value of gustatory stimuli. (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)     

Administration of corticosterone after the first downshift trial enhances consummatory successive negative contrast.

Rats given access to a 32% sucrose solution and then downshifted to a 4% solution exhibit less contact with the sipper tube than unshifted controls always given access to 4% solution. This phenomenon, called consummatory successive negative contrast, was facilitated in Experiment 1 by a posttrial injection of corticosterone (3 mg/kg) administered immediately after the first downshift trial. Experiment 2 demonstrated that this facilitatory effect of posttrial corticosterone does not occur when administered 3 hr after the first downshift trial. These results support the hypothesis that corticosterone strengthens an aversive emotional component elicited by the surprising downshift in reward magnitude during the initial downshift trial. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of frustration in successive positive contrast.

Attempted to replicate the essential features of L. Crespi's (see record 1943-01494-001) study as it relates frustration to positive contrast, using 40 male Sprague-Dawley rats. Experimental Ss were shifted from large to small incentive before being shifted back to large incentive to test for positive contrast. The 2nd shift was made when Ss were running slowly, on the assumption that this reflected frustration from the 1st shift. Comparison with controls showed a significant positive contrast under 2 drive levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Training interviewers to eliminate contrast effects in employment interviews.

Previous findings indicate that contrast effects are a potentially serious source of error in interviewers' ratings of job applicants. The present 4 experiments with undergraduates (N = 80) attempted to eliminate these errors. The failure of an anchoring treatment, and the combination and strengthening of the warning and anchor treatments reveal that contrast effects are a surprisingly tenacious source of rating error. However, an intensive workshop incorporating basic learning principles was successful in eliminating contrast effects as well as some other sources of interviewer error. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The overlearning-extinction effect and successive negative contrast in honeybees (Apis mellifera).

In 3 experiments with 169 free-flying honeybees, the overlearning-extinction effect previously demonstrated by the present authors (see record 1982-09095-001) was replicated under different conditions and shown to depend on magnitude of reinforcement. The effect appeared in training with a 50% sucrose solution but not with a 20% solution. Results prompted a 4th experiment, with 25 Ss, in which successive negative contrast was demonstrated. Ss were disturbed to find the 20% solution on a distinctive target that always before had been baited with the 50% solution. It is concluded that the overlearning-extinction effect is an instance of contrast and can be understood in terms of frustration engendered by unrealized anticipation of reinforcement. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Radio-frequency lesions of the thalamus produce delayed-nonmatching-to-sample impairments comparable to pyrithiamine-induced encephalopathy in rats.

Rats were trained and matched on a delayed-nonmatching-to-sample (DNMTS) task and randomly assigned to treatment. In Exp 1, radio-frequency (RF) lesions were aimed at lateral portions of the internal medullary lamina (L-IML), midline thalamus (MT), mammillary bodies (MB), and the combination of MT and MB. In Exp 2, RF lesions were aimed at the fornix. After recovery, DNMTS was retrained at retention intervals of 3.0–28.0 sec, the critical retention level for 75% DNMTS accuracy was determined by a staircase procedure, and spontaneous exploration was observed in an open field. L-IML lesions produced significant deficits on DNMTS and exploratory behavior that were comparable to deficits on the same tasks in rats recovered from pyrithiamine-induced thiamine deficiency. Fornix lesions produced significant DNMTS deficits that were substantially smaller than for the L-IML group. The MT, MB, and MT?+?MB treatments had no significant effect on DNMTS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decremental carryover effects of sucrose ingestion in the negative anticipatory contrast procedure in rats.

To test for retrospective effects of sucrose ingestion in the anticipatory contrast procedure, 4 experiments examined intake of an initial 0.15% saccharin solution as a function of the unsignaled interspersing of days in which the 2nd solution was 32% sucrose or 0.15% saccharin. In Experiment 1, rats that received alternating saccharin-saccharin days and saccharin-sucrose days drank less saccharin on saccharin-only days, and on both days they drank less saccharin than a control group that received saccharin only. In Experiment 2, rats that received randomized saccharin-saccharin and saccharin-sucrose days drank less saccharin if, and only if, a sucrose day preceded. Experiments 3 and 4 used double and quadruple alternation of saccharin and sucrose days to examine persistence of the effects of a sucrose day. The results highlighted a retrospective carryover effect of sucrose that reduced intake of the initial saccharin solution and apparently was based on sucrose memories persisting over days. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of scopolamine and hippocampal lesions on negative patterning discrimination performance in rats.

Rats were trained in operant chambers to perform an appetitive negative patterning successive discrimination. They were required to respond to the left in response to a tone or click and right to a tone-click compound. Scopolamine and methyl scopolamine impaired performance accuracy and increased response latency and response omissions. Subsequent hippocampal aspiration lesions initially impaired accuracy, which later improved. Lesions decreased response latencies. Finally, the effects of scopolamine and methyl scopolamine were shown to be similar in lesioned and control rats, suggesting that the hippocampus is not involved in the actions of these drugs on this task. (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)