Are the basal ganglia purely motor structures? This review challenges that notion, presenting extensive evidence for the basal ganglia's crucial role, especially the dorsal striatum, in learning and memory. Although the mammalian basal ganglia have long been implicated in motor behavior, it is generally recognized that the behavioral functions of this subcortical group of structures are not exclusively motoric in nature. The research highlights the region's involvement in stimulus-response (S-R) association learning, or habit formation, drawing from neurobehavioral studies across various species. Extensive evidence now indicates a role for the basal ganglia, in particular the dorsal striatum, in learning and memory. In rats and monkeys, localized brain lesion and pharmacological approaches have been used to examine the role of the basal ganglia in S-R learning. In humans, study of patients with neurodegenerative diseases that compromise the basal ganglia, as well as research using brain neuroimaging techniques, also provide evidence of a role for the basal ganglia in habit learning. Several of these studies have dissociated the role of the basal ganglia in S-R learning from those of a cognitive or declarative medial temporal lobe memory system that includes the hippocampus as a primary component. Evidence suggests that during learning, basal ganglia and medial temporal lobe memory systems are activated simultaneously and that in some learning situations competitive interference exists between these two systems.
The Annual Review of Neuroscience provides comprehensive overviews of current neuroscience research. This paper aligns with the journal's focus by reviewing the learning and memory functions of the basal ganglia. The review synthesizes extensive evidence from various species to illustrate the basal ganglia's role in habit learning and its interaction with other memory systems.