Neuroleptic effects on acquisition and performance of learned behaviors: a reinterpretation

It is well-established that dopamine facilitates motor responsiveness. However, neuroleptics--drugs that block dopaminergic transmission--do not affect equally motor responses to environmental stimuli: responses to some stimuli seem completely preserved while responses to other stimuli are greatly disturbed. For example, escape responses to a noxious stimulus are typically preserved, even when avoidance to a cue predicting the noxious stimulus is absent. In this paper, we propose a connectionist account of this differential effect. We assume that dopamine determines the "gain" of the function relating the activation of a neural ensemble to its excitatory or inhibitory input. Because such a function is necessarily non-linear, we show that the influence of gain on whether a neural ensemble reaches a "threshold" of activation is critically different for low and high excitatory drives. This analysis makes specific predictions about the effect of neuroleptics on motor responses at different stages of training.