Basal ganglia
Also known as: basal nuclei, BG
A group of deep brain nuclei that coordinate voluntary movement, the learning of habits, and motivation. Central to Parkinson's disease.
The basal ganglia are a group of interconnected subcortical nuclei sitting deep within each cerebral hemisphere. Despite the older name, they are not really ganglia in the strict sense (peripheral nervous system clusters). The term has stuck for historical reasons.
They are central to selecting, initiating, and refining voluntary movement, and they also play important roles in habit learning, reward processing, and motivation.
What's inside
The major components are:
- Caudate nucleus and putamen, which together form the striatum. This is the main input region.
- Globus pallidus (internal and external segments), the main output region.
- Subthalamic nucleus, a small but critical regulatory hub.
- Substantia nigra, in the midbrain, which provides dopamine input.
These structures form loops with the cortex and thalamus, creating a control circuit that helps shape motor commands and other behaviours.
What it does
The basal ganglia act like a gating system. They:
- Help the cortex select which motor program to run, and suppress others
- Modulate the timing and amplitude of movement
- Encode habits (procedural learning), so that frequent actions can run with less conscious oversight
- Contribute to reward learning and motivation, via dopamine signals
When it goes wrong
Disorders of the basal ganglia produce striking symptoms:
- Parkinson's disease: degeneration of the substantia nigra leads to dopamine depletion in the striatum, producing tremor, rigidity, and slow movement
- Huntington's disease: progressive degeneration of the striatum produces involuntary movements and cognitive decline
- Hemiballismus: damage to the subthalamic nucleus, often by small stroke, produces sudden flinging movements of the opposite limbs
- Dystonia and tics also involve basal ganglia dysfunction
In neuroimaging
Caudate, putamen, and globus pallidus volumes are part of any standard subcortical segmentation. Changes are reported in studies of Parkinson's disease, Huntington's, age-related decline, and certain psychiatric conditions.
Related terms
Gray matter
The darker, neuron-rich tissue that forms the outer cortex and the deep nuclei of the brain — where most signal processing happens.
Thalamus
A pair of large nuclei deep in the centre of the brain that act as the relay station for almost all sensory and motor information.
Parkinson's disease
A neurodegenerative disease that affects movement, mood, and cognition through the loss of dopamine-producing neurons in the brainstem.