The limbic circuit for response vigour

Motivation can be defined as the amount of energy an animal puts into actions to achieve goals. This not a static property but can be learned. Recently, abstract models have been developed for this kind of learning which propose that tonic dopamine is responsible to energise behaviour. However the underlying circuitry is still not understood and it is still unclear how tonic dopamine acts on the motor system to energise behaviour. In this paper we present a limbic system model of response invigoration which is based on neurophysiological data and anatomical connections. We argue that the indirect pathway from NAcc core D2 neurons via the ventral pallidum to the SNr conveys response vigour, while the direct pathway from NAcc core D1 neurons is responsible for action selection. Once this detailed anatomically mapped circuit has been established we then condense this realistic model into an abstract model which then shows that tonic DA acts in a multiplicative way on the motor output and thus is able to energise behaviour. We demonstrate the model with both a simulated and real robot experiment.