Figure 8.

Timecourse of the internal variables of a single NAcc neuron during a reward omission trial. After the conditioning phase, CS2 is presented alone. The NAcc neuron which was selective for US2 during conditioning is recorded: its membrane potential m(t) in red, the weighted sum of excitatory inputs from vmPFC in blue and its up- or down-state s(t) in green. The firing rate of the neuron is the positive part of the membrane potential: the firing rate becomes only non-zero shortly at the time where reward is expected but omitted.