Learning and Reversal Learning in the Subcortical Limbic System: A Computational Model

We present a biologically inspired model of the sub-cortical nuclei of the limbic system that is capable of performing reversal learning in a food seeking task. In contrast to previous models, the reversal is modeled by the inhibition of the previously learned behavior. This allows for the reinstatement of behavior to recur quickly as observed in animal behavior. In this model learning is achieved by implementing Isotropic Sequence Order learning and a third factor (ISO-3) that triggers learning at relevant moments. This third factor is modeled by phasic and tonic dopaminergic activity which respectively enable LTP to occur during acquisition, and LTD to occur when adjustments in learned behaviors are required. It will be shown how the nucleus accumbens (NAc) core uses conditioned reinforcers to invigorate instrumental responding while relatively strong LTD in the shell influences the core through a shell-ventral pallido-medio dorsal pathway. This pathway functions as a feed forward switching mechanism and enables behavioral flexibility.