Figure 10.

Time delay required to achieve a correct response to a stimulus of a given strength, with very low, low, normal, and high tonic dopamine. The absence of points means that, with the given stimulus and the given dopamine level, no acceptable response was gated by the basal ganglia and so no cortical neuron reached the activation threshold. The simulations show that, in case of stimuli of medium strength (a ranging between 0.8 and 0.9), the time required to achieve a valid response crucially depends on the dopamine level: higher levels of dopamine result in faster responses compared with lower levels. Conversely, when the stimulus is high (>0.9), the temporal response is scarcely affected by the dopamine level. Furthermore, in case of low dopamine, the network is able to gate only stimuli of sufficient strength (approximately a > 0.8) but it neglects stimuli of lower amplitude.