Jean-Claude Dreher

7 février 2012

Centre de Sciences Cognitives, Reward and decision making team, ISC, Bron

Neural coding of computational factors affecting decision making

invité par Guillaume Masson

Abstract : We constantly need to make decisions that can result in rewards of different magnitudes and different probabilities. To characterize the neural coding of computational factors affecting value-based decision making, it is first necessary to understand how they are coded in the brain when no choice needs to be done. This is the approach we took in the past few years using intra-cranial recordings in patients with epilepsy and fMRI in healthy controls to understand how computational factors such as reward magnitude, probability or uncertainty (maximal for reward probability=0.5) are coded in the human brain. Moreover, when facing a choice between several options, neuroimaging approaches on value-based decision-making assume that the brain computes the subjective value of outcomes expected from alternative options, weighing the likely benefits and costs resulting from an action. We recently used model-based fMRI to test whether the human brain uses separate valuation systems for rewards associated with two types of decision costs : delay and effort. Our data reveal that the human brain uses distinct valuation subsystems for different types of costs, reflecting in opposite fashion delayed reward and future energetic expenses. We also investigated common and specific brain regions responding to experienced value for different types of rewards, comparing brain responses for primary (erotic stimuli) and secondary rewards (money). Our results showed both a core reward system processing experienced value regardless of reward type and a functional organization in the orbitofrontal cortex along a postero-anterior axis according to reward type, with the anterior part responding exclusively to money and the posterior and medial part responding exclusively to erotic stimuli. In addition, we showed that genetically-influenced variations in dopamine transmission modulate the response of brain regions involved in anticipation and reception of rewards, and also provided evidence of neurofunctional modulation of the reward system by gonadal steroid hormones in humans. These findings establish a neurobiological foundation for understanding the impacts of genes and gonadal steroids hormones modulating dopamine transmission on vulnerability to drug abuse and neuropsychiatric diseases. Together, these results indicate that the combination of computational approach, molecular genetics, endocrinology and neuroimaging now helps to clarify the influences of basic biological mechanisms on reward and decision making processes.
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