Figure 6.

Negative symptoms in schizophrenia. (A) Chorley and Seth (2011) developed a model demonstrating how dopamine reward prediction error signals may be learned through the balance of excitatory and inhibitory projections. Excitatory signals from sensory areas fire phasically and drive dopamine neurons during the time of the stimulus (S) and the reward (R). Inhibitory signals from the striatum, on the other hand, also drive dopamine neurons, resulting in a constant firing rate during the time of the reward when the stimulus is predictive of the reward. (B) Our model suggests that the D2 state should affect striatum projections to dopamine neurons (top). That is, a high D2 state would increase the strength of inhibition on DA neurons, resulting in an overall lower firing rate for DA neurons and a dip in response at the time of the reward, despite the stimulus being predictive of the reward. Because PFC neurons that project to the striatum are driven by the corollary discharge (CD) in our model, an abnormal corollary discharge, as may be occurring in schizophrenic patients, could ultimately lead to abnormal DA responses (bottom).