Espresso Reward Learning, Hold the Dopamine: Theoretical Comment on Robinson et al. (2005).

Question: Is dopamine needed for reward learning? Answer: No--at least, not in the brain of a caffeinated dopamine-deficient (DD) mutant mouse. That is the conclusion of an important paper in this issue by S. Robinson, S. M. Sandstrom, V. H. Denenberg, and R. D. Palmiter (see record 2005-01705-001). Those authors demonstrate that reward learning can proceed normally in the brains of DD mice, even though they contain no dopamine at the time of learning, if the mice are given caffeine just before learning. Caffeine activates the DD mice by a nondopaminergic mechanism, allowing them to learn where to obtain food reward in a T-maze runway. Their reward-learning-without-dopamine is revealed on a subsequent test day, when dopamine function is restored by L-dopa administration. Robinson et al. conclude that dopamine is not needed for normal learning about rewards, or for hedonic "liking" of rewards during learning, but rather specifically for a motivational "wanting" component of reward, such as incentive salience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Local dopamine production in the dorsal striatum restores goal-directed behavior in dopamine-deficient mice.

To determine whether dopamine signaling in the dorsal striatum is sufficient for performance of goal-directed behaviors, local dopamine production was restored in the dorsal striatum of dopamine-deficient (DD) mice through viral-mediated gene therapy. Virally rescued DD (vrDD) mice were tested for learning of an appetitive T-maze task designed to measure goal-directed behavior. The results indicate that in contrast with the performance of DD mice that have dysregulated dopamine signaling, vrDD mice were able to perform the T-maze task and reverse their behavior as well as sham-operated control mice. The authors conclude that finely tuned dopaminergic signaling within the dorsal striatum is sufficient for performance of goal-directed behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Testing the incentive-sensitization theory with at-risk drinkers: Wanting, liking, and alcohol consumption.

Motivational models of addiction typically propose that alcohol and drugs are desired because of their hedonic effects (i.e., increasing pleasure or reducing distress). In contrast, the incentive-sensitization theory proposes that wanting motivation and liking motivation are separable and that after repeated substance use, motivation shifts from liking to wanting. Using a sample of 85 at-risk drinkers (as defined by the National Institute on Alcohol Abuse and Alcoholism), in the current study we examined the separability of liking motivation and wanting motivation for alcohol and whether years of drinking experience was associated with an increased role for wanting motivation and a decreased role for liking motivation. Consumption was measured with a free-drinking task. Wanting motivation was assessed immediately before drinking, and liking was assessed immediately after drinking had begun. The results indicated that (a) wanting motivation predicted variance of consumption unique from that accounted for by liking motivation, (b) longer drinking experience was associated with a decreased relation between liking motivation and consumption, and (c) longer drinking experience was not associated with an increased relation between wanting motivation and consumption. The results provide partial support for the incentive-sensitization theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Increased liking for a solution is not necessary for the attenuation of neophobia in rats.

Recent evidence suggests that liking and wanting of food rewards can be experimentally dissociated (e.g., Berridge, 1996); this dissociation extends to attenuated neophobia in the present study. Rats tend to eat less of a novel food than a familiar food, a phenomenon called neophobia. The present experiments evaluated whether attenuation of neophobia by prior exposure reflects enhanced liking of the flavor using the Taste Reactivity (TR) test. In Experiment 1, rats given five 10-s TR trials with water or various concentrations of saccharin solution (0.1%, 0.2%, 0.5%) did not show a change in the number of hedonic reactions displayed across trials. However, in a subsequent consumption test from a bottle containing 0.25% saccharin solution, rats with no prior saccharin exposure (group water) consumed less than rats with prior saccharin exposure; that is they displayed neophobia. In Experiment 2, whether rats received five 10-s TR trials with water or 0.5% saccharin solution, they did not display a difference in hedonic reactions to 0.25% saccharin solution in two 5-min TR test trials. These results suggest that the attenuation of neophobia is evidenced as an increase in the tendency to approach a bottle containing the flavored solution (wanting), but not as an enhanced liking of that solution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Outcome-specific satiety reveals a deficit in context-outcome, but not stimulus- or action-outcome, associations in aged Tg2576 mice.

The onset of Alzheimer's disease (AD) is often accompanied by changes in emotion, motivation, and goal-directed behavior. The production of beta-amyloid is thought to be a major and early contributor to the pathogenesis of AD. The present study tested the hypothesis that amyloid pathology present in the amygdala, frontal cortex, and hippocampus of Tg2576 mice would disrupt the development of instrumental- and/or Pavlovian-outcome associations. The results showed that both instrumental- and Pavlovian-conditioned behaviors were sensitive to outcome devaluation (Experiments 1 & 2) and that Pavlovian cues influenced goal-directed actions associated with the same outcome (Experiment 2) in Tg2576 mice. In contrast, context mediated Pavlovian-conditioned behaviors in aged (Experiment 3a) but not young (Experiment 3b) Tg2576 mice were insensitive to outcome devaluation. Aged Tg2576, nevertheless, successfully acquired a simple context discrimination at the same rate as control mice. We conclude that amyloid pathology in aged Tg2576 mice may specifically disrupt context-outcome associations supported by the hippocampus and/or its interaction with the amygdala. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Dissociable onset of cognitive and motivational dysfunctions following neonatal lesions of the ventral hippocampus in rats.

This research examined cognitive and motivational processes at different developmental stages in rats with neonatal ventral hippocampus (VH) lesions, an approach used to model schizophrenia. In Experiment 1, performance in a T-maze alternation task was assessed on postnatal days (PNDs) 22 and 23. VH-lesioned rats displayed a severe deficit relative to controls. In Experiment 2, behaviorally naive rats were tested for spontaneous alternation at PND 29. Alternation was intact in VH-lesioned rats only when successive alternations were separated by >5 s. In Experiment 3, motivation was tested in a cost-benefit T-maze task and in a saccharine-water preference test. Between PNDs 22-37, behaviorally naive rats with neonatal VH lesions displayed weaker saccharine preference than controls, but the 2 groups did not differ on the cost-benefit task. At adulthood, between PNDs 56-72, the difference on saccharine preference persisted and an impairment on the cost-benefit task emerged. Overall, these results suggest that working memory deficits observed at the weaning stage were not secondary to spontaneous alternation or motivation dysfunctions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cooperative problem solving by tufted capuchin monkeys (Cebus apella): Spontaneous division of labor, communication, and reciprocal altruism.

Using an experimentally induced cooperation task, the authors investigated whether tufted capuchin monkeys (Cebus apella) share the following 3 characteristics of cooperation with humans: division of labor, communication, and reciprocal altruism. In Experiment 1, the authors trained individual monkeys to perform the necessary sequence of actions for rewards and tested them in pairs to assess whether they could solve the task by spontaneously dividing the sequence of actions. All pairs solved this task. In Experiment 2, monkeys worked in the cooperation task and a task requiring no partner help. They looked at the partner significantly longer in the former task than in the latter, but communicative intent could not be determined. In Experiment 3, only 1 of 2 participants obtained a reward on each trial. Monkeys maintained cooperation when their roles were reversed on alternate trials. Their cooperative performances demonstrated division of labor; results suggest task-related communication and reciprocal altruism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cooperatively breeding cottontop tamarins (Saguinus oedipus) do not donate rewards to their long-term mates.

This study tested the hypothesis that cooperative breeding facilitates the emergence of prosocial behavior by presenting cottontop tamarins (Saguinus oedipus) with the option to provide food rewards to pair-bonded mates. In Experiment 1, tamarins could provide rewards to mates at no additional cost while obtaining rewards for themselves. Contrary to the hypothesis, tamarins did not demonstrate a preference to donate rewards, behaving similar to chimpanzees in previous studies. In Experiment 2, the authors eliminated rewards for the donor for a stricter test of prosocial behavior, while reducing separation distress and food preoccupation. Again, the authors found no evidence for a donation preference. Furthermore, tamarins were significantly less likely to deliver rewards to mates when the mate displayed interest in the reward. The results of this study contrast with those recently reported for cooperatively breeding common marmosets, and indicate that prosocial preferences in a food donation task do not emerge in all cooperative breeders. In previous studies, cottontop tamarins have cooperated and reciprocated to obtain food rewards; the current findings sharpen understanding of the boundaries of cottontop tamarins’ food-provisioning behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Personal relative deprivation, delay discounting, and gambling.

Several lines of research have provided evidence for a relation between personal relative deprivation and gambling. Despite this knowledge, little is known about possible psychological mechanisms through which personal relative deprivation exerts its influence on gambling. The authors of this research sought to examine one such mechanism: the desire for immediate rewards. Using complementary approaches to studying psychological mechanisms, they tested in four studies the general hypothesis that personal relative deprivation translates into gambling urges and behavior in part via increased desires for immediate, even if smaller, rewards. Study 1 showed that an experimental manipulation of personal relative deprivation increased participants' preferences for smaller-sooner over larger-later rewards during a delay-discounting task. Studies 2 and 3 showed that a decreased willingness to delay gratification led to increased gambling behavior. Study 4 showed that preferences for smaller-sooner over larger-later rewards statistically mediated the relation between self-reported personal relative deprivation and gambling urges among a community sample of gamblers. The implications and potential applications of these findings are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

NMDA receptor involvement in spatial delayed alternation in developing rats.

Two experiments examined the effect of the noncompetitive NMDA receptor antagonist, dizocilpine maleate (MK-801), on spatial working memory during development. Rats were trained on spatial delayed alternation (SDA) in a T-maze after ip administration of 0.06 mg/kg MK-801, 0.1 mg/kg MK-801, or saline on postnatal days (P) P23 and P33 (Experiment 1), or following bilateral intrahippocampal administration of 2.5 or 5.0 υg per side MK-801 or saline on P26 (Experiment 2). In Experiment 1, MK-801 dose-dependently impaired SDA learning at both ages. Because the same doses of systemic MK-801 have no effect on T-maze position discrimination learning, impairment of SDA by MK-801 likely reflects disruption of spatial working memory. Both doses of MK-801 abolished acquisition of SDA performance in Experiment 2. Disruption of hippocampal plasticity may account for the effects produced by systemic MK-801 administration. These results confirm and extend earlier lesion studies by implicating plasticity of hippocampal neurons in the ontogeny of spatial delayed alternation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotional and motivational changes after bilateral lesions of the globus pallidus.

This study investigated motivational changes in a 44 year-old man (PJ) who developed considerable reduction in spontaneous activity and speech, flat affect, social withdrawal, loss of interest, inability to "feel," and lack of concern regarding his medical condition after bilateral, focal, anoxic lesions of the globus pallidus. PJ and 30 male controls performed a task designed to parse hedonic evaluation, or liking, from incentive motivation, or wanting. Affective stimuli were presented on a computer screen and subjects controlled viewing time by pressing keys. PJ's liking and wanting of unpleasant stimuli was similar to that of controls. In response to pleasant stimuli, PJ showed normal ratings of wanting and hedonic appreciation, but significantly reduced viewing time or made no responses. Active withdrawal from liked stimuli could constitute the basic mechanism underlying poor motivation and social withdrawal associated with globus pallidus damage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fornix lesions can facilitate acquisition of the transverse patterning task: a challenge for "configural" theories of hippocampal function

Configural theories of hippocampal function predict that hippocampal dysfunction should impair acquisition of the transverse patterning task, which involves the concurrent solution of three discrimination problems: A+ versus B-; B+ versus C-; and C+ versus A-. The present study tested this prediction in rats using computer-graphic stimuli presented on a touchscreen. Experiment 1 assessed the effects of fornix lesions when the three problems were introduced sequentially (phase 1: A+ vs B-; phase 2: A+ vs B-, B+ vs C-; phase 3: A+ vs B-, B+ vs C-, C+ vs A-). Fornix lesions significantly facilitated acquisition of the complete transverse patterning task (phase 3) but had no effect on the number of sessions or errors required to attain criterion during phase 1 or phase 2. In experiment 2, in which all three problems were presented concurrently from the outset of training, fornix-lesioned animals outperformed control animals during the seventh block of acquisition trials and were not impaired during any stage of acquisition. Importantly, these same animals were significantly impaired on two allocentric spatial tasks: T-maze alternation (experiments 1 and 2) and the Morris Swim Task (experiment 1). These results contradict the predictions of configural theories of hippocampal function and cast doubt on the popular notion that spatial learning is a special case of configural learning.     

Lisuride prevents learning and memory impairment and attenuates the increase in extracellular dopamine induced by transient global cerebral ischemia in rats

In this experiment, we tested the efficacy of neuroprotection with lisuride, a dopamine agonist, using the 4-vessel occlusion rat model. Functional improvement was evaluated with two behavior tests exploring learning and memorization capacity in the rat, the Morris water maze and the 14-unit T-maze, 18 days after ischemia. Extracellular dopamine levels during ischemia were determined in search of a possible neuroprotection mechanism. Dopamine and its metabolites, DOPAC and HVA, as well as the serotonin metabolite, 5-HIAA, were assayed with HPLC-EC, in striatal extracellular fluid obtained by in vivo microdialysis in the awake rat. Lisuride was administered at a total dose of 10 ng by continuous intrastriatal infusion or at the dose of 0.5 mg/kg by i.p. infusion, 160 minutes before onset of ischemia for the neurochemical study and at the dose of 0.5 mg/kg via i.p. infusion, 1 hour before occlusion of the carotid arteries, for the behavior tests. Behavioral testing showed significantly better recovery in both sets of behavioral tests, with more pronounced positive results with the 14-unit T-maze, in comparison with the saline-treated animals. Microdialysis confirmed a significant attenuation of the ischemia-induced dopamine surge, whatever the mode of administration, compared with saline-treated animals. These results show that lisuride offers significant neuroprotection from the effect of experimental transient global forebrain cerebral ischemia in the rat; the mechanism would imply, at least in part, reduced levels of extracellular dopamine.     

Reward prediction in primate basal ganglia and frontal cortex

Reward information is processed in a limited number of brain structures, including fronto-basal ganglia systems. Dopamine neurons respond phasically to primary rewards and reward-predicting stimuli depending on reward unpredictability but without discriminating between rewards. These responses reflect 'errors' in the prediction of rewards in correspondence to learning theories and thus may constitute teaching signals for appetitive learning. Neurons in the striatum (caudate, putamen, ventral striatum) code reward predictions in a different manner. They are activated during several seconds when animals expect predicted rewards. During learning, these activations occur initially in rewarded and unrewarded trials and become subsequently restricted to rewarded trials. This occurs in parallel with the adaptation of reward expectations by the animals, as inferred from their behavioral reactions. Neurons in orbitofrontal cortex respond differentially to stimuli predicting different liquid rewards, without coding spatial or visual features. Thus, different structures process reward information processed in different ways. Whereas dopamine neurons emit a reward teaching signal without indicating the specific reward, striatal neurons adapt expectation activity to new reward situations, and orbitofrontal neurons process the specific nature of rewards. These reward signals need to cooperate in order for reward information to be used for learning and maintaining approach behavior.     

Muscarinic receptor antagonism of the nucleus accumbens core causes avoidance to flavor and spatial cues.

Pharmacological blockade of muscarinic receptors in the nucleus accumbens reduces food intake and instrumental behaviors that are reinforced by food delivery. Nucleus accumbens muscarinic antagonism may specifically suppress the hedonic or reinforcing effects of food, thus blocking its capacity to direct behavior. Alternatively, muscarinic receptor blockade may cause a negative hedonic state that interferes with appetitive learning and food intake. In these experiments, rats received infusions of scopolamine methyl bromide (10 μg/0.5 μl) into the nucleus accumbens core, following exposure to a novel flavor of liquid diet (Experiment 1) or prior to being placed into a place preference apparatus (Experiment 2). In both experiments, nucleus accumbens muscarinic receptor antagonism caused subsequent avoidance of the paired cue (flavor or spatial location). This effect was specific to cholinergic manipulation; no conditioned taste avoidance was observed after pairing the novel flavor with nucleus accumbens core antagonism of N-methyl-D-aspartate, dopamine D?, or opioid receptors (Experiment 3). These experiments confirm previous reports of a critical role for striatal acetylcholine in modulating goal-directed behaviors, but suggest caution when interpreting behavioral effects of pharmacological manipulation of striatal acetylcholine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning from text with diagrams: Promoting mental model development and inference generation.

Two experiments investigated learning outcomes and comprehension processes when students learned about the heart and circulatory system using (a) text only, (b) text with simplified diagrams designed to highlight important structural relations, or (c) text with more detailed diagrams reflecting a more accurate representation. Experiment 1 found that both types of diagrams supported mental model development, but simplified diagrams best supported factual learning. Experiment 2 replicated learning effects from Experiment 1 and tested the influence of diagrams on novices' comprehension processes. Protocol analyses indicated that both types of diagrams supported inference generation and reduced comprehension errors, but simplified diagrams most strongly supported information integration during learning. Visual representations appear to be most effective when they are designed to support the cognitive processes necessary for deep comprehension. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Achievement-Based Rewards and Intrinsic Motivation: A Test of Cognitive Mediators.

This study assessed how rewards impacted intrinsic motivation when students were rewarded for achievement while learning an activity, for performing at a specific level on a test, or for both. Undergraduate university students engaged in a problem-solving activity. The design was a 2 × 2 factorial with 2 levels of reward in a learning phase (reward for achievement, no reward) and 2 levels of reward in a test phase (reward for achievement, no reward). Intrinsic motivation was measured as time spent on the experimental task and ratings of task interest during a free-choice period. A major finding was that achievement-based rewards during learning or testing increased participants' intrinsic motivation. A path analysis indicated that 2 processes (perceived competence and interest-internal attribution) mediated the positive effects of achievement-based rewards in learning and testing on intrinsic motivation. Findings are discussed in terms of the cognitive evaluation, attribution, and social-cognitive theories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of sphingolipids on T lymphocyte activation

Two experiments are reported which examined the viability of motor output hypothesis as an explanation for manual asymmetries in goal-directed movement. Experiment 1 isolated the variability due to force generation by directly assessing precision of force production during an isometric wrist flexion task. Experiment 2 examined the additional role of externally based and internally created timing patterns on the performance of a repetitive force production task. Virtually no effects involving hand were apparent in either experiment. These findings provide no support for a hypothesis based solely on motor output to adequately account for hand differences in the performance of rapid, goal-directed movement.     

Hedonic and sensory characteristics of odors conditioned by pairing with tastants in humans.

Animals readily acquire positive odor-taste hedonic associations, but evidence for this in humans remains weak and was explored further. Retronasal pairing of odors with sucrose or salty stimuli (Experiment 1) increased the rated sweetness of sucrose-paired odors without altering liking, although changes in odor pleasantness correlated with sucrose liking. Experience of odors with sucrose or quinine by sweet likers (Experiment 2) found increased pleasantness and sweetness for sucrose-paired odors, whereas quinine-paired odors became less liked and more bitter. Odor-sucrose pairings in sweet likers and dislikers (Experiment 3) found increased sweetness in both groups but increased odor liking only in likers. These data suggest that evaluative and sensory learning are dissociable and that evaluative changes are sensitive to individual differences in sweet liking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impaired timing precision produced by striatal D2 receptor overexpression is mediated by cognitive and motivational deficits.

Increased striatal dopamine D2 receptor activity is thought to contribute to the pathophysiology of schizophrenia. To model this condition in mice, Kellendonk et al. (2006) generated transgenic mice that selectively overexpress the D2 receptor in striatum (D2OE). Drew et al. (2007) reported that D2OE mice display deficits in interval timing and motivation. The present study further explored the impaired timing in D2OE mice. Experiment 1 assessed the role of motivation in producing timing deficits in the peak procedure and found that performance in D2OE mice was improved by increasing motivation. In addition, performance was impaired in control mice when motivation was decreased. In Experiment 2, we found that D2OE mice have no timing impairment when tested using the bisection task, a procedure in which the measure of timing performance is less influenced by motivation to respond. In Experiment 3, we also used the bisection task and found selective impairment in timing of long durations in D2OE mice. These results suggest that striatal D2 overexpression impairs timing by decreasing motivation and through its impact on working memory and/or sustained attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)