Thu, 21 Aug 2008 15:19:56 BST CiteULike: awooga's O'doherty http://www.citeulike.org/user/awooga/author/O'doherty CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/awooga/article/467922 <i>Neuron, Vol. 49, No. 1. (5 January 2006), pp. 157-166.</i><br /><br />Food preferences are acquired through experience and can exert strong influence on choice behavior. In order to choose which food to consume, it is necessary to maintain a predictive representation of the subjective value of the associated food stimulus. Here, we explore the neural mechanisms by which such predictive representations are learned through classical conditioning. Human subjects were scanned using fMRI while learning associations between arbitrary visual stimuli and subsequent delivery of one of five different food flavors. Using a temporal difference algorithm to model learning, we found predictive responses in the ventral midbrain and a part of ventral striatum (ventral putamen) that were related directly to subjects' actual behavioral preferences. These brain structures demonstrated divergent response profiles, with the ventral midbrain showing a linear response profile with preference, and the ventral striatum a bivalent response. These results provide insight into the neural mechanisms underlying human preference behavior. Predictive neural coding of reward preference involves dissociable responses in human ventral midbrain and ventral striatum. JP O'doherty TW Buchanan B Seymour RJ Dolan doi:10.1016/j.neuron.2005.11.014 Neuron, Vol. 49, No. 1. (5 January 2006), pp. 157-166. 2006-01-18T01:28:49-00:00 2006 Neuron 0896-6273 49 1 157 166 dopamine fmri reinforcement-learning striatum http://www.citeulike.org/user/awooga/article/1127132 <i>J Neurophysiol, Vol. 97, No. 2. (February 2007), pp. 1621-1632.</i><br /><br />When deciding between different options, individuals are guided by the expected (mean) value of the different outcomes and by the associated degrees of uncertainty. We used functional magnetic resonance imaging to identify brain activations coding the key decision parameters of expected value (magnitude and probability) separately from uncertainty (statistical variance) of monetary rewards. Participants discriminated behaviorally between stimuli associated with different expected values and uncertainty. Stimuli associated with higher expected values elicited monotonically increasing activations in distinct regions of the striatum, irrespective of different combinations of magnitude and probability. Stimuli associated with higher uncertainty (variance) elicited increasing activations in the lateral orbitofrontal cortex. Uncertainty-related activations covaried with individual risk aversion in lateral orbitofrontal regions and risk-seeking in more medial areas. Furthermore, activations in expected value-coding regions in prefrontal cortex covaried differentially with uncertainty depending on risk attitudes of individual participants, suggesting that separate prefrontal regions are involved in risk aversion and seeking. These data demonstrate the distinct coding in key reward structures of the two basic and crucial decision parameters, expected value, and uncertainty. Reward value coding distinct from risk attitude-related uncertainty coding in human reward systems. PN Tobler JP O'doherty RJ Dolan W Schultz doi:10.1152/jn.00745.2006 J Neurophysiol, Vol. 97, No. 2. (February 2007), pp. 1621-1632. 2007-02-27T12:49:44-00:00 2007 J Neurophysiol 0022-3077 97 2 1621 1632 dopamine fmri reward striatum vta