Basal ganglia

The basal ganglia are interconnected subcortical brain nuclei that help select and regulate actions, shape movement, and support learning and other functions.

Direct pathway: A basal ganglia circuit that facilitates selected actions by reducing inhibitory output to the thalamus and brainstem. Its disinhibitory route helps release actions chosen for execution.
Striatum: The largest input region of the basal ganglia, comprising the caudate nucleus and putamen in humans. It receives extensive cortical input and begins many basal ganglia pathways.
Parkinson's disease: A progressive neurological disorder associated with loss of dopamine-producing neurons in the substantia nigra pars compacta. Dopamine loss disrupts basal ganglia circuits and causes characteristic movement difficulties.
Motor cortex: Cortical regions that plan and execute voluntary movements. Basal ganglia circuits influence motor cortical activity through recurrent thalamic loops.
Action selection: The process by which an organism chooses among competing possible actions. How basal ganglia circuits implement selection across contexts remains under active study.
Indirect pathway: A basal ganglia circuit that suppresses actions through a sequence involving the external globus pallidus and subthalamic nucleus. Its additional inhibitory steps help suppress competing actions.
Globus pallidus: A basal ganglia structure with external and internal segments that have distinct circuit roles. Its two segments participate differently in indirect-pathway processing and basal ganglia output.
Huntington's disease: An inherited neurodegenerative disorder caused by a pathogenic expansion in the HTT gene. Early striatal degeneration alters action control and can produce involuntary movements.
Cerebellum: A hindbrain structure involved in movement coordination, timing, prediction, and motor learning. It also shapes movement, but uses distinct circuitry and is not part of the basal ganglia.
Motor control: The processes by which the nervous system plans, coordinates, and regulates movement. Basal ganglia contributions extend beyond movement initiation to the organization of behavior.

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