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At least 253 records · Page 14Linked to original sources
PubMed2000

Delay activity of orbital and lateral prefrontal neurons of the monkey varying with different rewards.

We examined neuronal activity in the orbitofrontal cortex (OFC) in relation to reward expectancy and compared findings with those of the lateral prefrontal cortex (LPFC) in the monkey. Activity of OFC neurons was examined in a delayed reaction time task where every four trials constituted one block within which three kinds of rewards and no reward were delivered in a fixed order. More than half of OFC delay neurons were related to the expectancy of delivery or nodelivery of a reward as the response outcome, while some neurons showed nature-of-reward-specific anticipatory activity changes. These delay-related activities reflected the preference of the animal for each kind of reward and were modulated by the motivational state of the animal. LPFC neurons are reported to show nature-ofreward-specific anticipatory activity changes in a delayed response task when several different kinds of rewards are used. Such rewarddependent activity is observed in LPFC delay neurons both with and without spatially differential delay (working memory-related) activity. Although reward expectancy-related activity is commonly observed in both OFC and LPFC, it is suggested that the OFC is more concerned with motivational aspects, while the LPFC is related to both the cognitive and motivational aspects of the expectancy of response outcome.

Animal Feed↗
PubMed2005

Reward encoding in the monkey anterior cingulate cortex.

The anterior cingulate cortex (ACC) is known to play a crucial role in the fast adaptations of behavior based on immediate reward values. What is less certain is whether the ACC is also involved in long-term adaptations to situations with uncertain outcomes. To study this issue, we placed macaque monkeys in a probabilistic context in which the appropriate strategy to maximize reward was to identify the stimulus with the highest reward value (optimal stimulus). Only knowledge of the theoretical average reward value associated with this stimulus--referred to as 'the task value'--was available. Remarkably, in each trial, ACC pre-reward activity correlated with the task value. Importantly, this neuronal activity was observed prior to the discovery of the optimal stimulus. We hypothesize that the received rewards and the task value, constructed a priori through learning, are used to guide behavior and identify the optimal stimulus. We tested this hypothesis by muscimol deactivation of the ACC. As predicted, this inactivation impaired the search for the optimal stimulus. We propose that ACC participates in long-term adaptation of voluntary reward-based behaviors by encoding general task values and received rewards.

Action Potentials↗
PubMed2007

Solving the distal reward problem through linkage of STDP and dopamine signaling.

In Pavlovian and instrumental conditioning, reward typically comes seconds after reward-triggering actions, creating an explanatory conundrum known as "distal reward problem": How does the brain know what firing patterns of what neurons are responsible for the reward if 1) the patterns are no longer there when the reward arrives and 2) all neurons and synapses are active during the waiting period to the reward? Here, we show how the conundrum is resolved by a model network of cortical spiking neurons with spike-timing-dependent plasticity (STDP) modulated by dopamine (DA). Although STDP is triggered by nearly coincident firing patterns on a millisecond timescale, slow kinetics of subsequent synaptic plasticity is sensitive to changes in the extracellular DA concentration during the critical period of a few seconds. Random firings during the waiting period to the reward do not affect STDP and hence make the network insensitive to the ongoing activity-the key feature that distinguishes our approach from previous theoretical studies, which implicitly assume that the network be quiet during the waiting period or that the patterns be preserved until the reward arrives. This study emphasizes the importance of precise firing patterns in brain dynamics and suggests how a global diffusive reinforcement signal in the form of extracellular DA can selectively influence the right synapses at the right time.

Animals↗
PubMed2005

Differential brain activation according to chronic social reward frustration.

Neural correlates of reward frustration are increasingly studied in humans. In line with prediction error theory, omission of an expected reward is associated with relative decreases of cerebral activation in dopaminergic brain areas. We investigated whether a history of chronic work-related reward frustration influences this reward-dependent activation pattern by means of functional magnetic resonance imaging. Solving arithmetic tasks was followed by either monetary reward or omission of reward. Hyperactivations in the medial prefrontal, anterior cingulate and dorsolateral prefrontal cortex were observed in a group of healthy adults with high susceptibility to reward frustration as compared with a group with low susceptibility. Findings indicate a compromised ability of adapting brain activation among those suffering form chronic social reward frustration.

Adult↗
PubMedDate not supplied

Orbital prefrontal cortex and guidance of instrumental behavior of rats by visuospatial stimuli predicting reward magnitude.

The orbital prefrontal cortex (OPFC) is part of a circuitry mediating the perception of reward and the initiation of adaptive behavioral responses. We investigated whether the OPFC is involved in guidance of the speed of instrumental behavior by visuospatial stimuli predictive of different reward magnitudes. Unoperated rats, sham-lesioned rats, and rats with bilateral lesions of the OPFC by N-methyl-D-aspartate (NMDA) were trained in a visuospatial discrimination task. The task required a lever press on the illuminated lever of two available to obtain a food reward. Different reward magnitudes were permanently assigned to lever presses to respective sides of the operant chamber; that is, responses to one lever (e.g., the left one) were always rewarded with one pellet and responses to the other lever with five pellets. On each trial, the position of the illuminated lever was pseudorandomly determined in advance. Results revealed that OPFC lesions did not impair acquisition of the task, as the speed of conditioned responses was significantly shorter with expectancy of a high reward magnitude. In addition, during reversal, shift and reshift of lever position-reward magnitude contingencies and under extinction conditions, performance of the OPFC-lesioned and control groups did not differ. It is concluded that the OPFC in rats might not be critical for adapting behavioral responses to changes of stimulus-reward magnitude contingencies signaled by visuospatial cues.

Animals↗
PubMed2005

Involvement of NMDA and AMPA/KA receptors in the nucleus accumbens core in instrumental learning guided by reward-predictive cues.

The use of reward-predictive cues to guide behavior critically involves the nucleus accumbens. However, little is known regarding the role of ionotropic glutamate receptors in the core subregion of the nucleus accumbens (AcbC) in instrumental learning guided by reward-predictive cues. Here we examined the effects of an intra-AcbC blockade of NMDA and AMPA/KA receptors on the acquisition of an instrumental response in a reaction time (RT) task in rats. In this task, discriminative cues signaled in advance the upcoming reward magnitude (5 or 1 food pellet) associated with a lever release. During early acquisition (days 1-6) rats received daily bilateral injections of either the NMDA receptor antagonist AP5 (5.0 microg per side, n = 14), the AMPA/KA receptor antagonist CNQX (2.5 microg per side, n = 14) or vehicle (0.5 microL per side, n = 19). No treatment was given during late acquisition (days 7-12). The main result was that rats which received intra-AcbC injections of AP5 or CNQX during early acquisition exhibited a general RT increase of responses to high and low reward. However, treatment with AP5 and CNQX did not interfere with discriminative guidance of RTs by cue-associated reward magnitudes, i.e. during acquisition RTs of responses to expected high reward became significantly faster than RTs of responses to expected low reward. Our findings suggest that NMDA and AMPA/KA receptors in the AcbC play a critical role in invigorating responding during instrumental learning, but seem less important in guiding responding according to reward-predictive cues.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2006

Dopamine neuronal responses in monkeys performing visually cued reward schedules.

Dopamine neurons are important for reward-related behaviours. They have been recorded during classical conditioning and operant tasks with stochastic reward delivery. However, daily behaviour, although frequently complex in the number of steps, is often very predictable. We studied the responses of 75 dopamine neurons during schedules of trials in which the events and related reward contingencies could be well-predicted, within and across trials. In this visually cued reward schedule task, a visual cue tells the monkeys exactly how many trials, 1, 2, 3, or 4, must be performed to obtain a reward. The number of errors became larger as the number of trials remaining before the reward increased. Dopamine neurons frequently responded to the cues at the beginning and end of the schedules. Approximately 75% of the first-cue responsive neurons did not distinguish among the schedules that were beginning even though the cues were different. Approximately half of the last-cue responsive neurons depended on which schedule was ending, even though the cue signalling the last trial was the same in all schedules. Thus, the responses were related to what the monkey knew about the relation between the cues and the schedules, not the identity of the cues. These neurons also frequently responded to the go signal and/or to the OK signal indicating the end of a correctly performed trial whether a reward was forthcoming or not, and to the reward itself. Thus, dopamine neurons seem to respond to behaviourally important, i.e. salient, events even when the events have been well-predicted.

Animals↗
PubMed2005

Adaptive coding of reward value by dopamine neurons.

It is important for animals to estimate the value of rewards as accurately as possible. Because the number of potential reward values is very large, it is necessary that the brain's limited resources be allocated so as to discriminate better among more likely reward outcomes at the expense of less likely outcomes. We found that midbrain dopamine neurons rapidly adapted to the information provided by reward-predicting stimuli. Responses shifted relative to the expected reward value, and the gain adjusted to the variance of reward value. In this way, dopamine neurons maintained their reward sensitivity over a large range of reward values.

Adaptation, Physiological↗
PubMedDate not supplied

Dynamics of betting behavior under flat reward condition.

One of the missions of the cognitive process of animals, including humans, is to make reasonable judgments and decisions in the presence of uncertainty. The balance between exploration and exploitation investigated in the reinforcement-learning paradigm is one of the key factors in this process. Recently, following the pioneering work in behavioral economics, growing attention has been directed to human behaviors exhibiting deviations from the simple maximization of external reward. Here we study the dynamics of betting behavior in a simple game, where the probability of reward and the magnitude of reward are designed to give a "zero" expected net reward ("flat reward condition"). No matter how the subject behaves, there is on average no change in one's resources, and therefore every possible sequence of action has the same value. Even in such a situation, the subjects are found to behave not in a random manner, but in ways showing characteristic tendencies, reflecting the dynamics of brain's reward system. Our results suggest that brain's reward system is characterized by a rich and complex dynamics only loosely coupled with external reward structure.

Adult↗
PubMed2003

Impact of expected reward on neuronal activity in prefrontal cortex, frontal and supplementary eye fields and premotor cortex.

In several regions of the macaque brain, neurons fire during delayed response tasks at a rate determined by the value of the reward expected at the end of the trial. The activity of these neurons might be related either to the internal representation of the appetitive value of the expected reward or to motivation-dependent variations in the monkey's level of motor preparation or motor output. According to the first interpretation, reward-related activity should be most prominent in areas affiliated with the limbic system. According to the second interpretation, it should be most prominent in areas affiliated with the motor system. To distinguish between these alternatives, we carried out single-neuron recording while monkeys performed a memory-guided saccade task in which a visual cue presented early in each trial indicated whether the reward would be large or small. Neuronal activity accompanying task performance was monitored in the dorsolateral prefrontal cortex (PFC), the frontal eye field (FEF), a transitional zone caudal to the frontal eye field (FEF/PM), premotor cortex (PM), the supplementary eye field (SEF), and the rostral part of the supplementary motor area (SMAr). The tendency for neuronal activity to increase after cues that predicted a large reward became progressively stronger in progressively more posterior areas both in the lateral sector of the frontal lobe (PFC < FEF < FEF/PM < PM) and in the medial sector (SEF < SMAr). The very strong reward-related activity of premotor neurons was presumably attributable to the monkey's motivation-dependent level of motor preparation or motor output. This finding points to the need to determine whether reward-related activity in other nonlimbic brain areas, including dorsolateral prefrontal cortex and the dorsal striatum, genuinely represents the value of the expected reward or, alternatively, is related to motivational modulation of motor signals.

Action Potentials↗
PubMed2003

Correlation of primate caudate neural activity and saccade parameters in reward-oriented behavior.

Changes in the reward context are associated with changes in neuronal activity in the basal ganglia as well as changes in motor outputs. A typical example is found in the caudate (CD) projection neurons and saccade parameters. It raised the possibility that the changes in CD neuronal activity contribute to the changes in saccade parameters. To examine this possibility, we calculated the correlation coefficients (CORs) of the firing rates of each neuron with saccade parameters (peak saccade velocity and latency) on a trial-by-trial basis. We then calculated the mean CORs separately for two CD populations: reward-enhanced type neurons (RENs) that showed enhanced activity and reward-depressed type neurons (RDNs) that showed depressed activity when reward was expected. The activity of RENs was positively correlated with the saccadic peak velocity and negatively correlated with the saccade latency. The activity of RDNs was not significantly correlated with the saccade parameters. We further analyzed the CORs for RENs, a major type of CD neurons. First, we examined the time courses of the CORs using a moving time window (duration: 200 ms). The positive correlation with the saccade velocity and the negative correlation with the saccade latency were present not only in the peri-saccadic period but also during the pre- and postcue periods. Second, we asked whether the CORs with the saccade parameters were direction-selective. A majority of RENs were more active before contralateral saccades (contralateral-preferring neurons) and their activity was correlated more strongly with contralateral saccades than with ipsilateral saccades. A minority of RENs, ipsilateral-preferring neurons, showed no such preference. These results are consistent with the hypothesis that CD neuronal activity exerts facilitatory effects on contralateral saccades and that the effects start well before saccade execution. Furthermore, a multiple regression analysis indicated that changes in activity of some, but not all, CD neurons could be explained by changes in saccade parameters; a major determinant was reward context (presence or absence of reward). These results suggest that, while a majority of CD neurons receive reward-related signals, only some of them can make a significant contribution to change saccadic outputs based on expected reward.

Animals↗
PubMed1998

Influence of reward expectation on behavior-related neuronal activity in primate striatum.

Rewards constitute important goals for voluntary behavior. This study aimed to investigate how expected rewards influence behavior-related neuronal activity in the anterior striatum. In a delayed go-nogo task, monkeys executed or withheld a reaching movement and obtained liquid or sound as reinforcement. An initial instruction picture indicated the behavioral reaction to be performed and the reinforcer to be obtained after a subsequent trigger stimulus. Movements varied according to the reinforcers predicted by the instructions, suggesting that animals differentially expected the two outcomes. About 250 of nearly 1,500 neurons in anterior parts of caudate nucleus, putamen, and ventral striatum showed typical task-related activations that reflected the expectation of instructions and trigger, and the preparation, initiation, and execution of behavioral reactions. Strikingly, most task-related activations occurred only when liquid reward was delivered at trial end, rather than the reinforcing sound. Activations close to the time of reward showed similar preferences for liquid reward over the reinforcing sound, suggesting a relationship to the expectation or detection of the motivational outcome of the trial rather than to a "correct" or "end-of-trial" signal. By contrast, relatively few activations in the present task occurred irrespective of the type of reinforcement. In conclusion, many of the behavior-related neurons investigated in the anterior striatum were influenced by an upcoming primary liquid reward and did not appear to code behavioral acts in a motivationally neutral manner. Rather, these neurons incorporated information about the expected outcome into their behavior-related activity. The activations influenced by reward several seconds before its occurrence may constitute a neuronal basis for the retrograde effects of rewards on behavioral reactions.

Animals↗
PubMed2006

Delay aversion but preference for large and rare rewards in two choice tasks: implications for the measurement of self-control parameters.

BACKGROUND: Impulsivity is defined as intolerance/aversion to waiting for reward. In intolerance-to-delay (ID) protocols, animals must choose between small/soon (SS) versus large/late (LL) rewards. In the probabilistic discount (PD) protocols, animals are faced with choice between small/sure (SS) versus large/luck-linked (LLL) rewards. It has been suggested that PD protocols also measure impulsivity, however, a clear dissociation has been reported between delay and probability discounting. RESULTS: Wistar adolescent rats (30- to 46-day-old) were tested using either protocol in drug-free state. In the ID protocol, animals showed a marked shift from LL to SS reward when delay increased, and this despite adverse consequences on the total amount of food obtained. In the PD protocol, animals developed a stable preference for LLL reward, and maintained it even when SS and LLL options were predicted and demonstrated to become indifferent. We demonstrate a clear dissociation between these two protocols. In the ID task, the aversion to delay was anti-economical and reflected impulsivity. In the PD task, preference for large reward was maintained despite its uncertain delivery, suggesting a strong attraction for unitary rewards of great magnitude. CONCLUSION: Uncertain delivery generated no aversion, when compared to delays producing an equivalent level of large-reward rarefaction. The PD task is suggested not to reflect impulsive behavior, and to generate patterns of choice that rather resemble the features of gambling. In summary, present data do indicate the need to interpret choice behavior in ID and PD protocols differently.

Animals↗
PubMed2005

Conditioned nicotine withdrawal profoundly decreases the activity of brain reward systems.

Withdrawal from nicotine decreases the activity of brain reward systems, measured in rats by elevations of intracranial self-stimulation (ICSS) thresholds. This reward deficit is hypothesized to contribute to the persistence of the tobacco habit in tobacco smokers. Accumulating evidence suggests that aspects of drug withdrawal may become conditioned to previously neutral environmental stimuli via pavlovian conditioning processes. Here we investigated whether hedonically neutral stimuli repeatedly paired with nicotine withdrawal gained "affective valence" such that withdrawal-associated conditioned stimuli alone decreased brain reward function. Nicotine-dependent rats were presented with a light/tone conditioned stimulus and injected with the nicotinic receptor antagonist dihydro-beta-erythroidine (DHbetaE; 3 mg/kg) for 4 d consecutively; ICSS thresholds were assessed before and immediately after DHbetaE injection. On the test day, the rats were presented with the conditioned stimulus and injected with saline; next, ICSS thresholds were assessed. During conditioning sessions, DHbetaE elevated reward thresholds, and the magnitude by which thresholds were elevated increased during successive conditioning sessions. These data suggest that withdrawal-associated conditioned stimuli potentiated the magnitude of nicotine withdrawal as their motivational significance increased. Most importantly, on the test day, the conditioned stimulus alone elevated reward thresholds. Similarly, in a separate experiment, withdrawal-associated cues elevated reward thresholds in morphine-dependent rats. These data provide the first empirical verification that conditioned nicotine withdrawal may occur after exposure to withdrawal-paired cues. Moreover, these data demonstrate that withdrawal-paired conditioned stimuli attain negative affective valence and can decrease the activity of brain reward systems, mimicking the reward deficit observed during withdrawal from nicotine and other addictive drugs.

Animals↗
PubMed2004

Effects of preshift small magnitude of reward received during goalbox placements on the negative contrast effect.

During preshift, one experimental group of rats was given a large magnitude of food reward following a traversal of a straight alley and during a goalbox placement, while the other experimental group was given a small reward during goalbox placement and a large reward following a run. During postshift, all experimental groups were given a small reward of food following a traversal down the runway and during a goalbox placement. A control group was maintained on small reward during placements and following a traversal throughout the study. Only the group who received preshift large reward during placement and following a runway response ran slower to small reward during postshift than the control group maintained on small reward (negative contrast effect).

Animals↗
PubMed2000

[Psychometric properties of the French version of the Effort-Reward Imbalance model].

BACKGROUND: Two main models are currently used to evaluate psychosocial factors at work: the Job Strain model developed by Karasek and the Effort-Reward Imbalance model. A French version of the first model has been validated for the dimensions of psychological demands and decision latitude. As regards the second one evaluating three dimensions (extrinsic effort, reward, and intrinsic effort), there are several versions in different languages, but until recently there was no validated French version. The objective of this study was to explore the psychometric properties of the French version of the Effort-Reward Imbalance model in terms of internal consistency, factorial validity, and discriminant validity. METHODS: The present study was based on the GAZEL cohort and included the 10 174 subjects who were working at the French national electric and gas company (EDF-GDF) and answered the questionnaire in 1998. A French version of Effort-Reward Imbalance was included in this questionnaire. This version was obtained by a standard forward/backward translation procedure. RESULTS: Internal consistency was satisfactory for the three scales of extrinsic effort, reward, and intrinsic effort: Cronbach's Alpha coefficients higher than 0.7 were observed. A one-factor solution was retained for the factor analysis of the scale of extrinsic effort. A three-factor solution was retained for the factor analysis of reward, and these dimensions were interpreted as the factor analysis of intrinsic effort did not support the expected four-dimension structure. The analysis of discriminant validity displayed significant associations between measures of Effort-Reward Imbalance and the variables of sex, age, education level, and occupational grade. CONCLUSION: This study is the first one supporting satisfactory psychometric properties of the French version of the Effort-Reward Imbalance model. However, the factorial validity of intrinsic effort could be questioned. Furthermore, as most previous studies were based on male samples working in specific occupations, the present one is also one of the first to show strong associations between measures of this model and social class variables in a population of men and women employed in various occupations.

Adult↗
PubMed2001

Reward unpredictability inside and outside of a task context as a determinant of the responses of tonically active neurons in the monkey striatum.

Tonically active neurons (TANs) in the monkey striatum are involved in detecting motivationally relevant stimuli. We recently provided evidence that the timing of conditioned stimuli strongly influences the responsiveness of TANs, the source of which is likely to be the monkey's previous experience with particular temporal regularities in sequential task events. To extend these findings, we investigated the relationship of TAN responses to a primary liquid reward, the timing of which is more or less predictable to the monkey either outside of a task or during instrumental task performance. Reward predictability was indexed by the timing characteristics of the mouth movements. The responsiveness of TANs to reward increased with the range and variability of time periods before reward, notably when the liquid was delivered outside of a task. A change in the temporal order of events in a task context produced an increase of response to reward, suggesting an influence of the predicted nature of the event in addition to its time of occurrence. By contrast, we observed no substantial changes in neuronal activity at the expected time of reward when this event failed to occur, suggesting that these neurons do not appear to carry information about an error in reward prediction. These results demonstrate that TANs constitute a neuronal system that is involved in detecting unpredicted reward events, irrespective of the specific behavioral situation in which such events occur. The responses influenced by stimulus prediction may constitute a neuronal basis for the notion that striatal processing is crucial for habit learning.

Animals↗
PubMed2003

Differential response patterns in the striatum and orbitofrontal cortex to financial reward in humans: a parametric functional magnetic resonance imaging study.

Responses to monetary reward in humans have been assessed in a number of recent functional imaging studies, and it is clear that the neuronal substrates of financial reinforcement overlap extensively with regions responding to primary reinforcers, such as food. Money has the practical advantage of being an objectively quantifiable reinforcer. In this study, we exploit this advantage using a parametric functional magnetic resonance imaging design to look at the patterns of responding to systematically varying reward values. Twelve healthy volunteers were scanned during performance of a rewarded target detection task, in which the reward value varied between task blocks. We observed three distinct patterns of responding in different regions. Amygdala, striatum, and dopaminergic midbrain responded to the presence of rewards, regardless of value. In contrast, premotor cortex showed a linear increase in response with increasing reward value. Finally, medial and lateral foci of orbitofrontal cortex responded nonlinearly, such that response was enhanced for the lowest and highest reward values relative to the midrange. These results suggest functional distinction in response patterns within a distributed reward system.

Adult↗