Adrenal responses to reinforcement and extinction: Role of expectancy versus instrumental responding.

Measured plasma corticosterone levels during operant conditioning to determine the effect of reinforced and nonreinforced responding (extinction) on adrenal activation; Ss were 44 male Long-Evans rats. The influence of instrumental responding was assessed by comparing trained Ss with yoked Ss that received a matched reward schedule in the absence of an operant task. Reinforcement sessions resulted in a significant decrease in adrenal secretion at 20 min but not at 5 min, whereas extinction caused a rapid increase in corticosterone levels at 5 min and an even greater elevation at 20 min. Comparison of the operant and yoked Ss showed that this effect of reinforcement and extinction was not dependent on instrumental responding, but rather on the receipt or withdrawal of the expected reward. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of intrahippocampal administration of colchicine on incentive contrast and on radial maze performance.

Examined the behavior of rats given intradentate injections of colchicine (COL). In Exp 1, COL-treated, artificial cerebrospinal fluid (CSF)-treated, and untreated Ss did not differ in the intake of 32% and 4% sucrose solutions, nor did they differ in degree of successive negative contrast when the 32% solution was changed to 4% sucrose. In Exp 2, the COL-treated and CSF-treated Ss did not differ in degree of suppression in the intake of a 0.15% saccharin solution when it preceded 32% sucrose in once-daily pairings (anticipatory contrast), nor did they differ in reversal performance when saccharin–sucrose and saccharin–saccharin pairings were reversed. In Exp 3, the COL-treated Ss were substantially impaired in radial-arm maze performance compared with CSF-treated controls. Results suggest that a completely functioning hippocampus is not necessary for the memory of reward quality, the comparison of rewards, the suppression of behavior when reward is decreased, the formation of associations between 2 levels of reward, and the reversal of this association, as long as these processes are reflected in consummatory behavior. Data are interpreted in terms of differences between instrumental behavior and sensory memory and/or consummatory behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of conditional associations and operant delayed spatial response alternation: Effects of lesions in the medial prefrontal cortex.

8 male rats received bilateral lesions of the medial prefrontal cortex, another 8 rats were control operated. Three weeks after surgery, they were exposed to an autoshaping procedure in which the insertion of a lever into the experimental chamber (conditioned stimulus) always preceded the delivery of a response-independent food pellet (unconditioned stimulus). Ss with lesions acquired this conditional association faster than control. Ss as evidenced by the fact that they were more likely than control Ss to contact the conditioned stimulus at higher rates. Locomotor activity, observed in a standard open-field preceding autoshaping sessions, decreased for both groups of Ss with repeated exposure to the open-field, whereas differences between groups were not observed. Ss were also exposed to an operant delayed spatial response alternation procedure in which they were required to alternate responding between two levers that were inserted into the experimental chamber after delay intervals of either 5, 10, or 20 s had elapsed. Alternation response accuracy of Ss with lesions and control Ss decreased as a function of the duration of the delay interval, but control-operated Ss responded more accurately at each interval duration. Response accuracy increased with prolonged training for both groups of Ss, but faster for control than for Ss with lesions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hunger enhances the expression of calorie- but not taste-mediated conditioned flavor preferences.

Compared ethanol-mediated flavor preferences to preferences mediated by saccharin, which is sweet but noncaloric, and sucrose, which is both sweet and caloric in 4 experiments, using 74 Long-Evans rats. Ss learned to associate grape or orange flavor conditioned stimulus/stimuli (CS) with (1) ethanol or saccharin solution or (2) either the other unconditioned stimulus/stimuli (UCS) or plain tap water. They were then given 2-bottle choice tests between the flavor CSs apart from the UCSs. Flavors associated with 5% ethanol were preferred over saccharin-paired and water-paired flavors by sated Ss, and food deprivation during the choice test enhanced this preference. Flavors associated with 8% sucrose were preferred over water-paired flavors, and this preference was also enhanced by food deprivation. Flavors associated with 0.028% or 0.25% saccharin were preferred over flavors paired with water. In all cases, calorie-mediated preferences, at their highest levels, were stronger than taste-mediated preferences. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental differences in rats of suppressive effects of extinction as a function of extinction sessions.

Used 1 or 2 extinction sessions, 2 extinction procedures, and 2 ages of rats (23 and 95-120 days old) in a developmental analysis of the effects of extinction. Ss were 96 male Long-Evans hooded rats. The apparatus was a Y maze with 3 discriminably different arms. After 10 sessions of positive reinforcement, Ss received either 1 or 2 extinction sessions in which responding in 1 arm was no longer reinforced. Following extinction, responding in all 3 arms was again reinforced. Recovery data show that (a) the suppressive effects of extinction were greater for adults than infants and (b) the 2nd extinction session had a greater impact on the adults. Results support the hypothesis that younger rats have greater difficulty than older ones in inhibiting a response. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Uncontrollable shock proactively increases sensitivity to response-reinforcer independence in rats.

Learned helplessness theory predicts that animals exposed to inescapable shock acquire an expectancy of response-reinforcer independence, which proactively interferes with learning of response-reinforcer dependence. The theory also predicts that this expectancy can increase sensitivity to subsequent instances of response-reinforcer independence. Two experiments, with 42 male Holtzman rats, tested the latter prediction in a paradigm that minimized the confounding effects of shock-induced activity deficits. In Exp I, Ss were trained to respond for food, then given either escapable, inescapable, or no shock. Subsequently, they received 2 sessions of response-contingent food followed by sessions of noncontingent food deliveries. During this phase, inescapably shocked Ss decreased responding faster than did controls. Exp II replicated this finding with a different schedule of food delivery and a procedure that more directly minimized the possibility that the outcome was due to either direct or indirect shock-induced activity changes. Results support the prediction that uncontrollable aversive events can increase an animal's sensitivity to noncontingent response-reinforcer relationships. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Shock-induced suppression and potentiation of instrumental responding by rats.

A total of 20 female Long-Evans rats trained to press a retractable lever for food in a discrete trials situation were subsequently punished for responding. After suppression of responding, response-independent shocks were presented, with intensity increased on successive daily sessions. Shock induced responding, and number of responses, increased and response latencies decreased with increasing shock intensity. Control Ss initially given uncorrelated lever-food presentations responded significantly less to response-independent shock, and their responding was not systematically related to shock intensity. Results are consistent with the view that shock induces or disinhibits prepotent responses and inconsistent with the view that, to be effective in suppressing behavior, punishment must induce responses incompatible with the punished response. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extinction as a function of magnitude and percentage of food or sucrose reward.

64 male hooded rats in 8 groups were trained to run an alleyway and extinguished. For groups given food rewards, extinction performance was dependent on an interaction of the magnitude and percentage of reward in acquisition: in consistently reinforced Ss, large rewards led to slower running in extinction, but in partially reinforced Ss, large rewards led to faster running. With sucrose as the reward, however, large rewards (higher concentration) led to faster running in extinction irrespective of the schedule of reinforcement. These differences between food and sucrose are discussed in terms of frustration theory and sequential theory. The simplest interpretation, within the context of sequential theory, is to assume that different concentrations of sucrose, although differing in their reinforcing effects, do not produce discriminably different aftereffects. (French summary) (21 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decreased phospholipase D (PLD) activity in ceramide-induced apoptosis of human keratinocyte cell line HaCaT

Autoshaping conditioned responses (CRs) are reflexive and targeted motor responses expressed as a result of experience with reward. To evaluate the hypothesis that autoshaping may be a form of impulsive responding, within-subjects correlations between performance on autoshaping and impulsivity tasks were assessed in 15 Long-Evans hooded rats. Autoshaping procedures [insertion of retractable lever conditioned stimulus (CS) followed by the response-independent delivery of food (US)] were followed by testing for impulsive-like responding in a two-choice lever-press operant delay-of-reward procedure (immediate small food reward versus delayed large food reward). Delay-of-reward functions revealed two distinct subject populations. Subjects in the Sensitive group (n=7) were more impulsive-like, increasing immediate reward choices at longer delays for large reward, while those in the Insensitive group (n=8) responded predominantly on only one lever. During the prior autoshaping phase, the Sensitive group had performed more autoshaping CRs, and correlations revealed that impulsive subjects acquired the autoshaping CR in fewer trials. In the Sensitive group, acute injections of ethanol (0, 0.25, 0.50, 1.00, 1.50 g/kg) given immediately before delay-of-reward sessions yielded an inverted U-shaped dose-response curve with increased impulsivity induced by the 0.25, 0.50, and 1.00 g/kg doses of ethanol, while choice strategy of the Insensitive group was not influenced by ethanol dose. Ethanol induced impulsive-like responding only in rats that were flexible in their response strategy (Sensitive group), and this group also performed more autoshaping CRs. Data support the hypothesis that autoshaping and impulsivity are linked.     

Effects of selective forebrain noradrenaline loss on behavioral inhibition in the rat.

In Exp I, virtually total depletion of cortical and hippocampal noradrenaline (NA) by stereotaxic injection of 6-hydroxydopamine into the fibers of the dorsal noradrenergic bundle produced no impairment in acquisition learning of a runway response for food reward by 10 male Wistar rats. Extinction of this response, once learned, was markedly slower in the treated group than in 10 controls, the treated animals perseverating in rapid running to the goal box even with no food present there. Similarly, in Exp II with the same Ss, no impairment was found on acquisition of a continuously reinforced leverpressing response for food. Extinction of this response, however, was again slower in the treated group. Exp III showed that the subsequent acquisition of a successive light-dark discrimination task was also slower in the same treated Ss, with these animals perseverating in responding to the negative stimulus. Although selective forebrain NA loss does not impair the acquisition of appetitive responses, the suppression of responses in the absence of reward is impeded. A parallel is drawn with those effects found classically after surgical lesion to the hippocampus. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reinforcement contrast effects in rats following experimental definition of a dimension of reinforcement magnitude.

Administered magazine training in 2 experiments to female albino Sprague-Dawley rats under 1 of 3 basic conditions: a 3,000-Hz tone followed by (a) 1 food pellet, (b) 10 food pellets, or (c) a quasi-random mixture of both 1 and 10 food pellets. Ss then learned to press a lever for either a 1-pellet or a 10-pellet reward. Results reveal significant and long-lasting negative-reinforcement contrast. When Ss pressed for 1 pellet after a mixed 1-and-10 pellet pattern during magazine training, they learned to lever-press more slowly than if they had been magazine trained with just the 1-pellet reward. Data do not show positive contrast, however. Results suggest that rats may form "abstractions" about patterns of reinforcing events to which a given reinforcer is compared when it is used to facilitate the acquisition of a new response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The hippocampus and reward: Effects of hippocampal lesions on progressive-ratio responding.

Two experiments investigated the effects of ibotenic-acid lesions of the hippocampus on food-rewarded performance under a progressive-ratio 10 schedule of reinforcement. The results of Experiment 1 indicated that rats with hippocampal lesions showed profound increases in breakpoint and enhancements in the efficiency of responding. In a second experiment the same rats were challenged with prefeeding, increases in the height of the response lever, and the substitution of sucrose-based for grain-based reward pellets. Responding in both groups was similarly reduced by prefeeding and increases in the effortfulness of responding, but lesioned rats were significantly more responsive to the change to sucrose reward. Overall, the results indicated that hippocampal damage increased responding by enhancing the activational or hedonic properties of the delivered food pellets, while not affecting food-motivation or the motor capacity to respond. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Septal lesions and incentive expectancies in rats.

Tested male albino Wistar rats with bilateral septal lesions on a multiple DRL schedule with large and small rewards. The lesion produced less efficient DRL performance under both conditions. Small rewards produced more efficient DRL responding in controls and brain-damaged Ss. A 2nd study investigated runway conditioning under immediate, delayed, and no reward. Septal lesions increased running speeds with immediate reward, maintained faster speeds during the early delayed-reward trials, but produced no differences during extinction. A 3rd experiment investigated the effects of immediate and delayed rewards on auditory discrimination learning in septal and control Ss. Brain-damaged Ss showed inferior discrimination performance with delayed rewards but not with immediate rewards. Data suggest that septal lesions alter cognitive strategies (i.e., expectancies) based on incentive characteristics. (French abstract) (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeons remember briefly trained spatial location-food associations over extended time periods.

A novel procedure was used to assess pigeons' memory for spatial location. Ss received brief 16-min sessions in large transparent Plexiglas chambers from which room cues were visible. A pecking key-feeder combination was mounted on each wall of the chamber. Each day, one randomly selected pecking key-feeder combination provided intermittent grain reward. Perseveration of responding to the key that had provided food during the previous session clearly demonstrated that the pigeons remembered the location for periods of up to 72 hr. The results are interpreted in terms of associative memory and suggest that the associative-nonassociative memory distinction provides a useful framework for understanding animals' performance on spatial memory tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Midazolam administered to rats induces anterograde amnesia for changes in reward magnitude.

L. P. Crespi (1942) showed that rats trained to run an alley for a large food reward slowed down when shifted to a small reward. This effect is usually interpreted as an aversive emotional response to reward reduction (A. Amsel, 1958). Benzodiazepines attenuate the behavioral effects of reward reduction (C. F. Flaherty, 1990), but the emphasis has been on their anxiolytic, not memory-impairing, effects. Researchers trained rats (175–200 g) to run an alley for food until asymptote was reached. Reward magnitude was then either decreased (Experiment 1) or increased (Experiment 2). The benzodiazepine midazolam (1 mg/kg ip), injected immediately prior to a decrease or increase in reward magnitude, impaired the later retention of both changes in a manner consistent with anterograde amnesia. The findings suggest that the memory-impairing effects of benzodiazepines may, at least in part, influence the response to reward reduction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Saccharin aversion in alloxan-diabetic rats.

Performed 4 experiments with male Sprague-Dawley rats (n = 103) in which the saccharin ingestion of alloxan-diabetic, alloxan-nondiabetic, and controls was measured in a 2-choice preference situation. Results indicate that under a wide variety of procedures alloxan-diabetic Ss reject saccharin, but alloxan-nondiabetic Ss do so only when they are exposed to saccharin immediately following the administration of alloxan. It is concluded that injection of alloxan can serve as the UCS for taste-aversion learning under a restricted set of conditions but that hyperglycemia induces a saccharin aversion independently of this associational mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned suppression of humoral immunity in the rat.

180 Charles River rats were conditioned by pairing consumption of a novel sodium saccharin drinking solution with the effects of an ip injection of 75 mg/kg cyclophosphamide, an immunosuppressive drug. Five and 10 days after conditioning, an experimental group (Group CS) was reexposed to the saccharin drinking solution. Control Ss (Group CSo) were conditioned but were not reexposed to saccharin. On Days 10, 15, or 25 after conditioning, Ss were injected ip with sheep erythrocytes, and independent subgroups were sampled for hemagglutinating antibody titer 4, 6, or 8 days later. Antibody titers 4 days after immunization were lower than values observed 6 and 8 days after immunization, and CS Ss had an attenuated antibody response. There were no significant differences between Group CSo and a group of placebo-treated Ss, but CS Ss had lower antibody titers than placebo-treated animals 4, 6, and 8 days after antigenic stimulation. Results suggest that reexposure to a CS may have long-lasting effects, and provide further documentation of conditioned immunopharmacologic effects and the impact of behavioral factors in modifying immunologic reactivity. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ingestional aversion learning in preweanling rats.

In 4 experiments, ingestional aversions were conditioned in 12- and 15-day-old Sprague-Dawley rats by infusing a .5% solution of saccharin into the oral cavity and following this oral infusion by the injection of lithium chloride. At both ages, Ss for which the saccharin exposure was followed by lithium injection within 2–3 min drank less when the saccharin solution was again presented by oral infusion 12 hrs later; such suppressions of intake were not observed in Ss that previously received the saccharin and lithium in an unpaired fashion (Exps I and III). Ingestional aversions were also learned by 12-day-olds when a 30-min interval was introduced between saccharin exposure and lithium toxicosis but not when toxicosis was delayed by 120 min (Exp II). In contrast, 15-day-olds learned aversions with both the 30- and 120-min-delay intervals (Exp III). Despite the absence of long-delay learning in 12-day-olds, ingestional aversions conditioned at 12 days of age were retained for 2 wks (Exp IV). Results provide further evidence of the associative abilities of neonatal rats and illustrate a developmental aspect of long-delay learning. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of ethanol on Pavlovian autoshaping in rats

Approach responses, consummatory behaviors, and directed motor responses maintained by food reward resemble autoshaping CRs and are increased by lower doses of ethanol. This study evaluated the effects of presession i.p. injections of ethanol doses (0.00, 0.25, 0.50, 0.70. or 1.00 g/kg) on the acquisition of lever-press autoshaping CR performance in groups of male Long-Evans hooded rats. Paired groups received 15 daily sessions of Pavlovian autoshaping procedures, wherein the insertion of a retractable lever for 5 s (CS) was followed by the response-independent presentation of food (US). Ethanol facilitated lever-press autoshaping CR acquisition, as revealed by dose-related increases in the number of trials on which CRs were performed. The form of the dose-effect curve was inverted U-shaped with maximal responding induced during sessions 1-5 by the 0.70 g/kg ethanol dose. A similar dose-effect curve was observed during sessions 11-15, revealing that the effects of ethanol on autoshaping CR performance were relatively stable. A pseudoconditioning control group injected presession with 0.50 g/kg ethanol received training wherein the food US was presented randomly with respect to the lever CS. Few lever-presses were performed by the Random 0.50 group, indicating that ethanol's effects on autoshaping CR acquisition and maintenance observed in the Paired 0.50 group were not due to its psychomotor activating effects. A non-injection control group performed more autoshaping CRs than did the control group injected presession with saline, indicating that daily presession i.p. injections per se suppress autoshaping CR performance. Results reveal that low doses of ethanol enhance Pavlovian conditioning of directed motor and consummatory-like responding maintained by food reward. Implications for autoshaping accounts of impulsivity and drug abuse are considered.     

The role of taste in dietary self-selection in rats.

Conducted 3 experiments with 78 male albino Harlan and Sprague-Dawley rats in which Ss were subjected to 2 degrees of gustatory deafferentation—either the chorda tympani was sectioned alone or in combination with the glossopharyngeal nerve and the pharyngeal branch of the vagus. Ss were then presented with 2 diets, only 1 of which contained protein. Findings reveal that, after surgery, deficits were observed in body weight, food and water intake, and diet selection that were proportional to the extent of deafferentation. Approximately 76% of the Ss increased protein and decreased carbohydrate intake, but all Ss continued to select a nutritionally balanced diet (Exp I). When subjected to a nutritional challenge of intragastric protein or carbohydrate supplementation, the Ss compensated for calories and nutrients by selectively adjusting oral intake (Exp II). In saccharin preference tests, the preference as well as the total consumption of the test solutions was reduced (Exp III). Results support the hypothesis that dietary selection pattern of an animal not only reflects intrinsic factors (metabolic/physiological state) but also extrinsic factors such as the pallatability and accessibility of the diet. Findings are contrasted to the effects of oral somatosensory deafferentation and are interpreted as a change in preference within the limits of metabolic requirements. The different roles/mechanisms of the 2 sensory systems in regard to dietary self-selection are discussed. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)