Reinforcement Learning in Cortical Networks

Reinforcement learning represents a basic paradigm of learning in artificial intelligence and biology. The paradigm considers an agent (robot, human, animal) that acts in a typically stochastic environment and receives rewards when reaching certain states. The agent’s goal is to maximize the expected reward by choosing the optimal action at any given state. In a cortical implementation, the states are defined by sensory stimuli that feed into a neuronal network, and after the network activity is settled, an action is read out. Learning consists in adapting the synaptic connection strengths into and within the neuronal network based on a (typically binary) feedback about the appropriateness of the chosen action. Policy gradient and temporal difference learning are two methods for deriving synaptic plasticity rules that maximize the expected reward in response to the stimuli.