A limbic system model for the control of release of tonic dopamine and its effect on response vigor
© Hattan and Porr; licensee BioMed Central Ltd. 2011
Published: 18 July 2011
It has been proposed that phasic dopamine activity is responsible for learning whereas tonic dopamine is rather responsible for the response vigour . In contrast to previous more abstract work on this topic we have created a biologically realistic limbic system model where the release of tonic dopamine controls the overall response vigour of a simulated agent and where the release of phasic dopamine controls learning. Tonic dopamine provides a signal similar to the average rate of reward suggested by Daw  and directly affects the response rate of the agent.
Here, we show how tonic dopamine is controlled by the sub-cortical nuclei of the limbic system, especially by the nucleus accumbens (NAc) shell and the ventral pallidum . By embedding these nuclei in a system level model of the limbic system we are able to generate tonic activity as seen in behavioural experiments. The NAc shell thereby learns new associations between rewards and stimuli which are then used to control the tonic dopamine which in turn controls the vigour. The learning which takes place in the shell is triggered by phasic dopamine and is implemented as a third factor .
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