[Functional neuroanatomy of implicit learning: associative, motor and habit]

The present review focuses on the neuroanatomy of aspects of implicit learning that involve stimulus-response associations, such as classical and instrumental conditioning, motor learning and habit formation.

These types of learning all require a progression in the acquisition of procedural information about 'how to do things' instead of 'what things are'. These forms of implicit learning share the neural substrate formed mainly by brain circuits involving basal ganglia, prefrontal cortex and amygdala. The relationship between pavlovian and instrumental learning is shown in the transference and autoshaping studies. There has been a resurgence of interest in habit learning because of the suggestion that addiction is a process that progresses from a reinforced response to a habit in which the stimulus-response association is supraselected and becomes independent of voluntary cognitive control. Dopamine has demonstrated to be involved in the acquisition of these procedures.

The different forms of procedural learning studied here all are characterized by stimulus-response-reinforcement associations, but there are differences between them in terms of the degree to which some of these associations or components are strengthened. These different patterns of association are partially regulated by the degree of involvement of the frontal-striatal-amygdala circuits.