Topic: reward basis vectors

The dominant theory of dopamine function in the basal ganglia system is model-free reinforcement learning (RL) where the dopaminergic neurons in the Ventral Tegmental Area (VTA) encode reward prediction errors which are used to modulate plasticity at cortico-striatal synapses so as to learn a value function of cortical states (Schultz et al 1998). However, a key assumption of this model (and model-free RL generally) is that the reward function being optimized is fixed, while for biological creatures the `reward function' can fluctuate over time depending on physiological state -- i.e. food is