Qualitative description of learning payoffs and costs.

(a) Operant conditioning chamber setup: a rat obtains a food pellet by pressing a lever. (b) Diagrams of changes in the weights G and N associated with lever-pressing at each stage of the experience presented in panel (a). In all diagrams, the black circles represent the cortical neurons selective for the state (being in the operant box), and the green and red circles represent the Go and No-Go populations of striatal neurons, respectively, selective for the action (pressing the lever). The thickness of the arrows linking the circles represents the connection strength between the respective neuron populations. The blue shading in the background indicates the strength of the immediate reinforcement, with a colour intensity proportional to the magnitude of reinforcement.