This study investigated the processing of increasing monetary reward in nonsmoking and smoking subjects. The choice of the subject populations has been motivated by the observation of differences between nonsmokers and smokers in response to rewarding stimuli in a previous study. Subjects performed a pattern recognition task with delayed response, while rCBF was measured with [H215O] PET. Correct responses to the task were reinforced with three different amounts of monetary reward. The subjects received the sum of the rewards at the end of the experiment. The results show that a cortico-subcortical loop, including the dorsolateral prefrontal cortex, the orbitofrontal cortex, the cingulate gyrus and the thalamus is involved in processing increasing monetary reward. Furthermore, the striatal response differentiates nonsmokers from smokers. Thus, we found significant correlations between rCBF increases in striatum and increasing monetary reward and between striatal rCBF increases and mood in nonsmokers, but not in smokers. Moreover, no significant mood changes among the different monetary rewards could be observed in smokers. We infer that the response of the striatum to reward is related to changes in subjective feelings. The differences between smokers and nonsmokers confirm our previous conclusions that the association between blood flow, performance, mood and amount of reward is more direct in nonsmokers.
"Further, accepting overcompensated offers was found to be associated with activity in the brain reward's system (Delgado et al., 2000, 2003, 2004; Knutson et al., 2001; Martin-Soelch et al., 2003). Finally, we found that the ability to protest without cost does not influence participants' tendency to do so, indicating that the cost involved in refusals is not sufficient to explain the lack of rejections. "
[Show abstract][Hide abstract] ABSTRACT: Human decision-making in situations of inequity has long been regarded as a competition between the sense of fairness and self-interest, primarily based on behavioral and neuroimaging studies of inequity that disfavor the actor while favoring others. Here, we use functional magnetic resonance imaging experiments to study refusals and protests using both favoring and disfavoring inequity in three economic exchange games with undercompensating, nearly equal, and overcompensating offers. Refusals of undercompensating offers recruited a heightened activity in the right dorsolateral prefrontal cortex (dlPFC). Accepting of overcompensating offers recruited significantly higher node activity in, and network activity among, the caudate, the cingulate cortex, and the thalamus. Protesting of undercompensating fixed offers activated the network consisting of the right dlPFC and the left ventrolateral prefrontal cortex and midbrain in the substantia nigra. These findings suggest that perceived fairness and social decisions are the results of coordination between evaluated fairness norms, self-interest and reward.
"Block design fMRI and PET studies do not allow for the dissociation of anticipatory and consummatory processes. Thus, the reported NAcc activity in studies using these methods (Aharon et al., 2001; Martin-Soelch et al., 2003) might well be a consequence of insufficient temporal resolution. Moreover, most reward paradigms lack a distinguishable anticipation phase because they do not make use of a reward predicting cue. "
[Show abstract][Hide abstract] ABSTRACT: Human behaviour is generally guided by the anticipation of potential outcomes that are considered to be rewarding. Reward processing can thus be dissected into a phase of reward anticipation and a phase of reward consumption. A number of brain structures have been suggested to be involved in reward processing. However, it is unclear whether anticipation and consumption are mediated by the same or different neural networks. We examined the neural basis of these processes using functional magnetic resonance imaging (fMRI) in an incentive delay task offering either money or social approval. In both conditions participants (N=28) were given a cue indicating potential reward. In order to receive reward a target button had to be pushed within a certain time window (adapted for individual reaction time). Cues triggering either monetary or social reward anticipation were presented sessionwise. Imaging was performed on a 1.5-Tesla Philips scanner in an event-related design. Anticipation of both reward types activated brain structures constituting the brain reward system including the ventral striatum. In contrast to the task independent activity in the anticipation phase, reward consumption evoked different patterns of activation for money and social approval, respectively. While social stimuli were mainly associated with amygdala activation, the thalamus was more strongly activated by the presentation of monetary rewards. Our results identify dissociable neural networks for the anticipation and consumption of reward. The findings implicate that the neural mechanisms underlying reward consumption are more modality-specific than those for reward anticipation, and that they are mediated by subjective reward value.
"We selected the ventral striatum as the prime a priori ROI for coding reward value, including its decrease with temporal delays (Elliott et al. 2000; Kable and Glimcher 2007; Knutson et al. 2005; Martin-Soelch et al. 2003; McClure et al. 2004, 2007; Tanaka et al. 2004; Tobler et al. 2007b; Yacubian et al. 2006). The ventral striatum includes the nucleus accumbens, the ventral caudate nucleus and putamen rostral to the anterior commissure. "
[Show abstract][Hide abstract] ABSTRACT: Delayed rewards lose their value for economic decisions and constitute weaker reinforcers for learning. Temporal discounting of reward value already occurs within a few seconds in animals, which allows investigations of the underlying neurophysiological mechanisms. However, it is difficult to relate these mechanisms to human discounting behavior, which is usually studied over days and months and may engage different brain processes. Our study aimed to bridge the gap by using very short delays and measuring human functional magnetic resonance responses in one of the key reward centers of the brain, the ventral striatum. We used psychometric methods to assess subjective timing and valuation of monetary rewards with delays of 4.0-13.5 s. We demonstrated hyperbolic and exponential decreases of striatal responses to reward predicting stimuli within this time range, irrespective of changes in reward rate. Lower reward magnitudes induced steeper behavioral and striatal discounting. By contrast, striatal responses following the delivery of reward reflected the uncertainty in subjective timing associated with delayed rewards rather than value discounting. These data suggest that delays of a few seconds affect the neural processing of predicted reward value in the ventral striatum and engage the temporal sensitivity of reward responses. Comparisons with electrophysiological animal data suggest that ventral striatal reward discounting may involve dopaminergic and orbitofrontal inputs.
Journal of Neurophysiology 02/2009; 101(3):1507-23. DOI:10.1152/jn.90730.2008 · 2.89 Impact Factor
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