|
|
|
Reward value and the orbitofrontalThe architecture of reward value coding in the human orbitofrontal cortex Sescousse, G., Redoute, J. & Dreher, C., Centre National de la Recherche Scientifique & University of Lyons The Journal of Neuroscience, (2010) 30(39) pp.13095-13104: doi:10.1523/JNEUROSCI.3501 2010 Keywords: Reward value, orbitofrontal, anterior cingulate, ventromedial prefrontal INTRODUCTION: We are conscious of emotions, and they allow us to assess the reward values of actions. Neuroscience now has a reasonable grasp of which areas of the brain process emotion. Without the emotion-based assessment of rewards, rational processing is not by itself adequate to deliver normal behaviour. While reasoning can be seen as working with or without consciousness, the subjective experience of emotion is closely entwined with the perception or assessment of future or current rewards. In fact, this ability to have a subjective preference might be seen as a way of distinguishing between conscious and non-conscious systems. In itself this does not take us any closer to understanding how consciousness actually arises, but it does give us an adaptive function for consciousness, and an idea of which brain processes to concentrate on, although a solution may still require the much resisted step into fundamental physics. Reward-directed behaviour involves brain areas including the ventral striatum, the anterior insula, the anterior cingulate cortex, the midbrain and the orbitofrontal and ventromedial prefrontal cortex. This paper looks at the functional division of the orbitofrontal cortex. Studies suggest that the orbitofrontal deals with a variety of types of reward values. It has been suggested that the brain has a common neural currency for comparing the various reward values, and that this integration may take place in the ventral striatum and the ventromedial prefrontal cortex. Studies have shown that reward value could be integrated in these areas for any type of reward. In a study performed by the authors, they attempted to compare the brain's processing of monetary rewards, with its processing of rewards in terms of erotic images. Monetary rewards were shown to use the anterior lateral region of the orbitofrontal cortex. This area is better developed in humans than in other species. Erotic images by contrast activated the posterior part of the lateral orbitofrontal cortex and also the medial orbitofrontal cortex. It was also found that patients with damage to the anterior orbitofrontal have difficulty with assessing indirect consequences as distinct from immediate consequences. Brain activity in these orbitofrontal regions increased with the intensity of reward only for types of reward in which those areas were specialised. By contrast, activity increased for both monetary and erotic rewards in the ventral striatum, the anterior cingulate cortex, the anterior insula and the midbrain. Other studies using rewards such as pleasant tastes have suggested a similar distinction between the posterior and anterior regions of the orbitofrontal. These studies points to the existence of both reward specific and reward non-specific systems in the brain. The bilateral amygdala was the only subcortical area to be activated in reward assessment and it was only activated by primary rewards such as erotic images and not by abstract rewards such as money. This area is more strongly connected to the posterior and medial orbitofrontal than to the anterior orbitofrontal. One distinction that is argued to emerge is between immediate or primary reward, and the more abstract or secondary quality of a monetary reward that can only be enjoyed over time. The authors argue that studies suggest that it is not the actual delay in benefiting from the monetary reward but its abstract nature that leads to it being processed in a different area. There have also been suggestions of a rather similar split in cognitive processing, with the posterior areas of the prefrontal cortex involved with immediate actions, and the anterior areas more involved with extended planning or abstract properties. It has often been proposed that the initial processing of reward values is subsequently converted into a common neural currency. A large number of studies support this view with the ventral striatum and ventromedial prefrontal indicated as the areas involved in this process. The actual experience of the reward may also be processed in these areas, and could aid decision taking if the reward is presented again. There is some disagreement between studies as to whether prediction error, (dealing with the failure of rewards to appear) is based on the dopamine neurons in the midbrain or on the ventral striatum. |
| Email: quantum-mind@blueyonder.co.uk Copyright © Quantum Mind 2012. Web design by 7Soft.co.uk. |