Wednesday 28 May 2003
Mammalian basal ganglia are associated with a variety of functions: motor control, cognition, emotions, and learning. In modern use the term ’ganglia’ is in this instance considered a misnomer; ’ganglion’ refers to concentrations of neural nuclei in the periphery only (for example those of the autonomic nervous system), and the term ’basal nuclei’ is preferred.
The five individual nuclei that make up the primate basal ganglia, along with their major subdivisions, are:
rostral basal nuclei
- the striatum, which consists of putamen and caudate nucleus
- external segment of the globus pallidus (GPe)
- internal segment of the globus pallidus (GPi)
caudal basal nuclei
- subthalamic nucleus (STN)
- substantia nigra (SN) : substantia nigra pars compacta (SNc), substantia nigra pars reticulata (SNr), substantia nigra pars lateralis (SNl)
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.
Extensive evidence now indicates a role for the basal ganglia, in particular the dorsal, in learning and memory.
One prominent hypothesis is that this brain region mediates a form of learning in which stimulus-response (S-R) associations or habits are incrementally acquired. Support for this hypothesis is provided by numerous neurobehavioral studies in different mammalian species, including rats, monkeys, and humans.
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.
hypoplasia of basal ganglia
Packard MG, Knowlton BJ. Learning and memory functions of the Basal Ganglia. Annu Rev Neurosci. 2002;25:563-93. PMID: 12052921