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PubMed2003

Delay discounting of real and hypothetical rewards.

The degree to which real and hypothetical rewards were discounted across delays ranging from 6 hr to 1 year was explored in a within-subjects design. An adjusting-amounts procedure was used to estimate the subjective value of real and hypothetical rewards at each delay. A hyperbolic discounting function provided a significantly better fit to individual participants' preferences than did an exponential function. No significant effect of reward type on degree of hyperbolic discounting or area under the discounting curves was detected. These findings offer some support for the validity of using hypothetical rewards to estimate discounting rates in substance-abusing and other populations, but caution is suggested because this support is gleaned from a failure to detect an effect of reward type.

Adolescent↗
PubMed1998

Expectation of reward modulates cognitive signals in the basal ganglia.

Action is controlled by both motivation and cognition. The basal ganglia may be the site where these kinds of information meet. Using a memory-guided saccade task with an asymmetric reward schedule, we show that visual and memory responses of caudate neurons are modulated by expectation of reward so profoundly that a neuron's preferred direction often changed with the change in the rewarded direction. The subsequent saccade to the target was earlier and faster for the rewarded direction. Our results indicate that the caudate contributes to the determination of oculomotor outputs by connecting motivational values (for example, expectation of reward) to visual information.

Animals↗
PubMed1996

Reward expectancy in primate prefrontal neurons.

The prefrontal cortex is important in the organization of goal-directed behaviour. When animals are trained to work for a particular goal or reward, reward 'expectancy' is processed by prefrontal neurons. Recent studies of the prefrontal cortex have concentrated on the role of working memory in the control of behaviour. In spatial delayed-response tasks, neurons in the prefrontal cortex show activity changes during the delay period between presentation of the cue and the reward, with some of the neurons being spatially specific (that is, responses vary with the cue position). Here I report that the delay activity in prefrontal neurons is dependent also on the particular reward received for the behavioural response, and to the way the reward is given. It seems that the prefrontal cortex may monitor the outcome of goal-directed behaviour.

Animals↗
PubMed2005

A role for lateral hypothalamic orexin neurons in reward seeking.

The lateral hypothalamus is a brain region historically implicated in reward and motivation, but the identity of the neurotransmitters involved are unknown. The orexins (or hypocretins) are neuropeptides recently identified as neurotransmitters in lateral hypothalamus neurons. Although knockout and transgenic overexpression studies have implicated orexin neurons in arousal and sleep, these cells also project to reward-associated brain regions, including the nucleus accumbens and ventral tegmental area. This indicates a possible role for these neurons in reward function and motivation, consistent with previous studies implicating these neurons in feeding. Here we show that activation of lateral hypothalamus orexin neurons is strongly linked to preferences for cues associated with drug and food reward. In addition, we show that chemical activation of lateral hypothalamus orexin neurons reinstates an extinguished drug-seeking behaviour. This reinstatement effect was completely blocked by prior administration of an orexin A antagonist. Moreover, administration of the orexin A peptide directly into the ventral tegmental area also reinstated drug-seeking. These data reveal a new role for lateral hypothalamus orexin neurons in reward-seeking, drug relapse and addiction.

Animals↗
PubMed2004

Human anterior cingulate neurons and the integration of monetary reward with motor responses.

The human dorsal anterior cingulate cortex (dACC) has been implicated in cognitive processes that have been proposed to play a role in integrating contextual information needed to select or modify appropriate motor responses. In humans, however, there has been little direct evidence tying the dACC to the integration of contextual information and behavioral response. We used single-neuron recordings from human subjects to evaluate the role of the dACC in reward-based decision making. Subjects undergoing planned surgical cingulotomy performed a task where they were instructed to make specific movements in response to changing monetary rewards. In many neurons, activity increased in response to a diminished reward, and was also predictive of the movement ultimately made. After dACC ablation, subjects made selectively more errors when they were required to change movement based on reward reduction. These findings suggest that the dACC in humans plays an important role in linking reward-related information with alternative actions.

Analysis of Variance↗
PubMed2003

Modifying children's food preferences: the effects of exposure and reward on acceptance of an unfamiliar vegetable.

OBJECTIVE: The aim of this study was to evaluate two interventions (one reward-based and one exposure-based) for increasing children's acceptance of an unfamiliar vegetable compared with a no-treatment control. It was predicted that the exposure condition would increase liking for, and consumption of, the vegetable relative to either the reward or control group. DESIGN: Using a randomized controlled design, participants were assigned to one of two intervention groups (exposure or reward) or to a no-treatment control condition, for a 2 week period. Liking for, and consumption of, red pepper was assessed before and after the treatment period. SETTING: The study was conducted in three primary schools in London. SUBJECTS: Parental consent was obtained for 49 out of a possible 72 children. INTERVENTIONS: Interventions comprised eight daily sessions during which participants in the exposure group were offered a taste of sweet red pepper and told that they could eat as much as they liked. Participants in the reward group were shown a sheet of cartoon stickers and told that they could choose one of them on condition that they ate at least one piece of the pepper. RESULTS: The exposure-based intervention significantly increased both liking (P=0.006) and consumption (P=0.03) compared with the control group. The outcome of the reward intervention was intermediate and did not differ significantly from the exposure or control conditions. CONCLUSIONS: Repeated exposure to the taste of unfamiliar foods is a promising strategy for promoting liking of previously rejected foods in children.

Child↗
PubMed2001

Brain reward circuitry and the regulation of energy balance.

Reward signals contribute to the regulation of energy balance by influencing switching between feeding and competing behaviors. Properties of natural rewards are mimicked by electrical stimulation of certain brain regions. The rewarding effect produced by stimulating the perifornical region of the hypothalamus is modulated by body weight and is attenuated both by leptin and insulin. Research is reviewed concerning the dependence of the rewarding effect of perifornical stimulation on long-term energy stores and the effects of two neuropeptides implicated in the regulation of energy balance, neuropeptide Y and corticotropin-releasing hormone. It is proposed that the potentiating effect of weight loss on perifornical self-stimulation is not tied to an increased propensity to eat or to an enhancement of food reward per se, but resembles the influence of long-term energy stores on non-ingestive behaviors that defend body weight, such as hoarding.

Animals↗
PubMed2003

Altered motivation and learning following opiate withdrawal: evidence for prolonged dysregulation of reward processing.

Opiate abuse has been associated with cognitive deficits in human addicts. To determine if prior opiate exposure alters the ability to learn, we trained animals in an instrumental learning task for a food reward. During a 2-week period after withdrawal, morphine-abstinent rats were significantly slower at learning an escalating fixed-ratio response for food reward compared to placebo-treated animals. When these same animals were trained in a conditioned suppression paradigm (two tone-shock pairings given in the operant box), the morphine-withdrawn animals showed greater retention by taking significantly longer to resume responding for food reward when the tone was presented. In a third experiment, morphine-abstinent rats withdrawn 2 or 5 weeks were tested for their ability to associate a highly palatable food reward with a specific environment using a place-conditioning paradigm. At 2 weeks postwithdrawal, morphine-abstinent rats did not show any significant place preference for a food they readily consumed, while placebo-treated rats readily learned to prefer the food-paired environment. At 5 weeks postwithdrawal, rats developed significantly less preference for food-associated cues, but more preference for morphine-associated cues, compared to placebo-treated animals. These data suggest that prior morphine exposure may have prolonged effects on the motivation for natural rewards, which in turn may compromise the ability of former addicts to overcome their addictions.

Animals↗
PubMed2004

Sensitization of psychomotor stimulation and conditioned reward in mice: differential modulation by contextual learning.

Incentive motivation theory ascribes a critical role to reward-associated stimuli in the generation and maintenance of goal-directed behavior. Repeated psychomotor stimulant treatment, in addition to producing sensitization to the psychomotor-activating effects, can enhance the incentive salience of reward-associated cues and increase their ability to influence behavior. In the present study, we sought to investigate this incentive sensitization effect further by developing a model of conditioned reinforcement (CR) in the mouse and investigating the effects of a sensitizing treatment regimen of amphetamine on CR. Furthermore, we assessed the role of contextual stimuli in amphetamine-induced potentiation of CR. We found that mice responded selectively on a lever resulting in the presentation of a cue previously associated with 30% condensed milk solution, indicating that the cue had attained rewarding properties. Prior treatment with amphetamine (4 x 0.5 mg/kg i.p.) resulted in psychomotor sensitization and enhanced subsequent responding for the CR. Furthermore, this enhancement of responding for the cue occurred independent of the drug-paired context, whereas the sensitized locomotor response was only observed when mice were tested in the same environment as that in which they had received previous amphetamine. These results demonstrate that the CR paradigm previously developed in the rat can be successfully adapted for use in the mouse, and suggest that behavioral sensitization to amphetamine increases the rewarding properties (incentive salience) of reward-paired cues, independent of the drug-paired context.

Analysis of Variance↗
PubMed2005

Mice with chronically elevated dopamine exhibit enhanced motivation, but not learning, for a food reward.

Dopamine has been critically implicated in learning and motivation, although its precise role remains to be determined. In order to investigate the involvement of dopamine in learning and motivation for a food reward, we used dopamine transporter knockdown mice (DAT KD) that have chronically elevated levels of extracellular dopamine. The present study demonstrates that chronically elevated dopamine enhances tendency to work for a food reward without apparent effects on Pavlovian and operant learning for this reward. The increase in dopamine is associated with elevated levels of dynorphin and Fos B expression in the dorsal caudate-putamen and the core but not the shell subregion of the nucleus accumbens. These data suggest that motivation to work, but not learning, for a food reward appears to be under the critical influence of tonic dopaminergic activity in discrete brain areas relevant for a reward-directed behavior.

Animals↗
PubMed2006

Food intake and reward mechanisms in patients with schizophrenia: implications for metabolic disturbances and treatment with second-generation antipsychotic agents.

Obesity is highly prevalent among patients with schizophrenia and is associated with detrimental health consequences. Although excessive consumption of fast food and pharmacotherapy with such second-generation antipsychotic agents (SGAs) as clozapine and olanzapine has been implicated in the schizophrenia/obesity comorbidity, the pathophysiology of this link remains unclear. Here, we propose a mechanism based on brain reward function, a relevant etiologic factor in both schizophrenia and overeating. A comprehensive literature search on neurobiology of schizophrenia and of eating behavior was performed. The collected articles were critically reviewed and relevant data were extracted and summarized within four key areas: (1) energy homeostasis, (2) food reward and hedonics, (3) reward function in schizophrenia, and (4) metabolic effects of the SGAs. A mesolimbic hyperdopaminergic state may render motivational/incentive reward system insensitive to low salience/palatability food. This, together with poor cognitive control from hypofunctional prefrontal cortex and enhanced hedonic impact of food, owing to exaggerated opioidergic drive (clinically manifested as pain insensitivity), may underlie unhealthy eating habits in patients with schizophrenia. Treatment with SGAs purportedly improves dopamine-mediated reward aspects, but at the cost of increased appetite and worsened or at least not improved opiodergic capacity. These effects can further deteriorate eating patterns. Pathophysiological and therapeutic implications of these insights need further validation via prospective clinical trials and neuroimaging studies.

Animals↗
PubMed2006

Antagonism of CRF receptors prevents the deficit in brain reward function associated with precipitated nicotine withdrawal in rats.

Nicotine dependence is a chronic mental illness that is characterized by a negative affective state upon tobacco smoking cessation and relapse after periods of abstinence. It has been hypothesized that cessation of nicotine administration results in the activation of brain corticotropin-releasing factor (CRF) systems that leads to the negative affective state of withdrawal. The aim of our experiments was to investigate the role of brain CRF systems in the deficit in brain reward function associated with the cessation of nicotine administration in rats. The intracranial self-stimulation procedure was used to assess to negative affective aspects of nicotine withdrawal as this procedure can provide a quantitative measure of emotional distress in rats. In the first experiment, mecamylamine induced a dose-dependent elevation in brain reward thresholds in nicotine-treated rats. In the follow-up experiment, it was shown that pretreatment with the corticotropin-receptor antagonist D-Phe CRF((12-41)) prevents the elevations in brain reward thresholds associated with precipitated nicotine withdrawal. In the third experiment, the effect of D-Phe CRF((12-41)) on the elevations in brain reward thresholds associated with spontaneous nicotine withdrawal was investigated. Administration of D-Phe CRF((12-41)) 6 h after the explantation of the nicotine pumps, did not result in a lowering of the brain reward thresholds. These findings indicate that antagonism of CRF receptors prevents, but not reverses, the deficit in brain associated with nicotine withdrawal. These data provide support for the hypothesis that a hyperactivity of brain CRF systems may at least partly mediate the initiation of the negative affective aspects of nicotine withdrawal.

Animals↗
PubMed2001

The influence of sensitivity to reward on reactivity to alcohol-related cues.

AIMS: To investigate the role of sensitivity to reward in mediating social drinkers' reactivity to alcohol cues. DESIGN: A standard cue-reactivity paradigm was employed. Two groups of social drinkers (heavy and light) were assessed after exposure to the sight, smell and taste of a neutral cue (water) and then an alcohol cue (glass of beer). SETTING: Sessions were conducted in a laboratory based environment. PARTICIPANTS: Twenty heavy (12 males, eight females) and 18 light social drinkers (seven males, 11 females) were recruited; mean age was 23.6 years. MEASUREMENTS: The Card Arranging Reward Responsivity Objective Test (CARROT), assessing behavioural responsiveness to a monetary incentive; urge to drink; positive affect; and the BAS scales, assessing sensitivity to reward. FINDINGS: Heavy drinkers displayed a significant increase in responsivity to rewards (i.e. CARROT) and self-reported urge to drink, but not positive affect, after exposure to alcohol. For the heavy drinkers, heightened sensitivity to reward (i.e. BAS scales) was significantly related to cue-elicited urge to drink and positive affect. CONCLUSION: The results are consistent with a conditioned appetitive motivational model of alcohol use and suggest that Gray's theory of personality may be of some benefit in explaining variation in reactivity responses.

Adolescent↗
PubMed2002

Transient changes in mesolimbic dopamine and their association with 'reward'.

Mesolimbic dopaminergic neurons modulate complex circuitry in the ventral forebrain involved in reward processing, although the precise function of the dopaminergic input is debated. Electrophysiological measurements have revealed that mesolimbic dopaminergic neurons can fire in either tonic or phasic modes, and that phasic firing accompanies the alerting or anticipatory phases of reward. However, the neurochemical relevance of this rapid neuronal discharge within the reward processing circuitry is not yet clear, in part because of difficulty in interpretation of extracellular dopamine measurements. Herein, the nature of the information provided by different neurochemical techniques is critically discussed. Classical methods of monitoring dopamine reveal changes in extracellular dopamine resulting from tonic neuronal activity, but do not have the temporal resolution to distinguish concentration transients. However, recent advances in dopamine sensors now enable transient dopamine concentrations resulting from phasic firing to be positively identified and followed on a physiologically relevant timescale. This has enabled demonstrations of discrete, phasic dopamine signals accompanying rewarding or alerting stimuli. Thus, enhanced dopamine release at terminals appears to be coincident with phasic electrical activity at cell bodies. These accumulating data promise to help unravel the precise role of phasic dopamine transmission in reward processing.

Animals↗
PubMed2000

Considerations upon the anatomical model of reward-based learning in the basal ganglia.

The nigrostriatal pathway appears to be very important in the reward-based learning. The dopaminergic neurons in the substantia nigra pars compacta (SNC) fire in relation to primary rewards and reward-conditioned stimuli, but not to rewards that are expected. It has been hypothesized that the anatomical framework for the selective response of these neurons is organized in the projections from some paralimbic areas in the frontal lobe to the striosomes of the caudate nucleus, which are also directly connected with the dopaminergic neurons of the SNC. Here, we present two additional pathways that may be related with this neurophysiological finding. We hypothesize that the connections of the paralimbic cortices with the ventral system of the basal ganglia and then with the thalamus and the hypothalamus, and the circuit ventral striatum-substantia nigra pars reticulata-thalamus-striatum could be also involved in the reward-based learning.

Basal Ganglia↗
PubMed2005

Dopamine D1 receptors involved in locomotor activity and accumbens neural responses to prediction of reward associated with place.

Predicting reward is essential in learning approach behaviors. Dopaminergic activity has been implicated in reward, movement, and cognitive processes, all essential elements in learning. The nucleus accumbens (NAc) receives converging inputs from corticolimbic information-processing areas and from mesolimbic dopamine neurons originating in the ventral tegmental area. Previously, we reported that in mice, a dopamine D2 receptor knockout (D2R-KO) eliminated the prereward inhibitory response, increased place-field size of NAc neurons, and reduced locomotor activity without marked change in intracranial self-stimulation (ICSS) behavior. The present study investigated the specific contribution of dopamine D1 receptor (D1R) in mediating reward, locomotor activity, and spatial associative processes and in regulating NAc neural responses. In contrast to D2R-KO animals, here we find D1R-KO in mice selectively eliminated the prereward excitatory response and decreased place-field size of NAc neurons. Furthermore, D1R-KO impaired ICSS behavior, seriously reduced locomotor activity, and retarded acquisition of a place learning task. Thus, the present results suggest that D1R may be an important determinant in brain stimulation reward (ICSS) and participates in coding for a type of reward prediction of NAc neurons and in spatial learning.

Animals↗
PubMed2006

Abolished cocaine reward in mice with a cocaine-insensitive dopamine transporter.

There are three known high-affinity targets for cocaine: the dopamine transporter (DAT), the serotonin transporter (SERT), and the norepinephrine transporter (NET). Decades of studies support the dopamine (DA) hypothesis that the blockade of DAT and the subsequent increase in extracellular DA primarily mediate cocaine reward and reinforcement. Contrary to expectations, DAT knockout (DAT-KO) mice and SERT or NET knockout mice still self-administer cocaine and/or display conditioned place preference (CPP) to cocaine, which led to the reevaluation of the DA hypothesis and the proposal of redundant reward pathways. To study the role of DAT in cocaine reward, we have generated a knockin mouse line carrying a functional DAT that is insensitive to cocaine. In these mice, cocaine suppressed locomotor activity, did not elevate extracellular DA in the nucleus accumbens, and did not produce reward as measured by CPP. This result suggests that blockade of DAT is necessary for cocaine reward in mice with a functional DAT. This mouse model is unique in that it is specifically designed to differentiate the role of DAT from the roles of NET and SERT in cocaine-induced biochemical and behavioral effects.

Animals↗
PubMed2002

The neural system that bridges reward and cognition in humans: an fMRI study.

We test the hypothesis that motivational and cognitive processes are linked by a specific neural system to reach maximal efficiency. We studied six normal subjects performing a working memory paradigm (n-back tasks) associated with different levels of monetary reward during an fMRI session. The study showed specific brain activation in relation with changes in both the cognitive loading and the reward associated with task performance. First, the working memory tasks activated a network including the dorsolateral prefrontal cortex [Brodmann area (BA) 9/46] and, in addition, in the lateral frontopolar areas (BA 10), but only in the more demanding condition (3-back task). This result suggests that lateral prefrontal areas are organized in a caudo-rostral continuum in relation with the increase in executive requirement. Second, reward induces an increased activation in the areas already activated by working memory processing and in a supplementary region, the medial frontal pole (BA 10), regardless of the level of cognitive processing. It is postulated that the latter region plays a specific role in monitoring the reward value of ongoing cognitive processes. Third, we detected areas where the signal decreases (ventral-BA 11/47 and subgenual prefrontal cortices) in relation with both the increase of cognitive demand and the reward. The deactivation may represent an emotional gating aimed at inhibiting adverse emotional signals to maximize the level of performance. Taken together, these results suggest a balance between increasing activity in cortical cognitive areas and decreasing activity in the limbic and paralimbic structures during ongoing higher cognitive processing.

Adolescent↗