A Guide to the Basal Ganglia
This article explains what “basal ganglia” are, where they are, and what they do. It also lists what the basal ganglia control in the body and discusses the associated medical conditions.
The basal ganglia are a group of nuclei below the cerebral cortex that are primarily responsible for motor control and other roles in the body, such as habit formation and helping you process emotions. These structures link together and communicate with each other to carry out complex functions.
The basal ganglia approve or reject movement signals the brain sends, called modulating inhibition, enabling the use of specific muscles when taking action. The basal ganglia also receive sensory information from other parts of the body and use it to refine movement.
The basal ganglia consist of five major nuclei:
- caudate nucleus
- globus pallidus
- subthalamic nucleus
- substantia nigra
The caudate, putamen, and globus pallidus are all part of the corpus striatum, which is the largest component of the basal ganglia. These structures are generally part of the basal ganglia. These nuclei have important roles they play separately, but they still connect to form a network.
Even though the basal ganglia perform different functions, their primary role is controlling voluntary movement.
The basal ganglia are in vertebrates’ brains, deep within the cerebral hemispheres.
The cerebral hemispheres are two connected parts of the brain that communicate with one another to control functions, such as motor actions, cognitive thought, and language. The word “basal” also means the ganglia are close to the base or bottom of the brain.
The main function of the basal ganglia involves motor control, but other areas they control include:
- planning and modulating movement
- fine-tuning movement
- decision making
- motivation and reward processing
- eye movements
- memory and focus
The corpus striatum is the largest part of the basal ganglia. It is also the main input site. This structure receives nerve supply from different cortical and subcortical structures.
The corpus striatum has two main divisions, including the dorsal striatum, which consists of the caudate nucleus and putamen, and the ventral striatum, which consists of the olfactory tubercle and the nucleus accumbens.
Other functional components of the basal ganglia include:
- The subthalamic nucleus: This is a small, oval-shaped structure that makes up a larger part of the subthalamus. It is one of the nuclei that health experts target for deep brain stimulation.
- The substantia nigra: This is a nucleus in the midbrain that connects with other brain stem nuclei. It comprises two nuclei — the dopaminergic pars compacta and the inhibitory pars reticulate. This structure has dopaminergic properties and plays an important role in movement and reward functions.
- The internal and external segments of the globus pallidus: These are two adjacent segments of a subcortical structure in the brain — the globus pallidus. The main function of this structure is to control conscious and proprioceptive movements. The external globus pallidus is an intrinsic nucleus and acts as a relay for information, while the internal globus pallidus is an output nucleus that sends information to the thalamus.
The basal ganglia comprise neurons that the internal parts of the globus pallidus and the substantia nigra project outward to the brain stem and thalamus. These neurons are the lenticular fasciculus and the ansa lenticularis. They are the major outputs of the basal ganglia.
Likewise, the basal ganglia also receive some inputs from different parts of the brain, such as the reticular formation of the brain stem, the thalamus, and the entire cerebral cortex.
Because the basal ganglia comprise structures that play important roles in the brain and body, any damage to or problems that affect these structures can cause medical conditions.
Some conditions that involve the basal ganglia include:
Parkison’s disease is the most common type of “parkinsonism,” an umbrella term for tremor, bradykinesia, and rigidity symptoms.
Parkinson’s disease results from the degeneration of dopaminergic neurons in the substantia nigra. These neurons produce dopamine, and when they experience damage, this makes it difficult for the basal ganglia to cause the release of inhibition required to make a movement.
Because of this, people with Parkinson’s disease often experience slow movement or difficulty initiating movement.
One of the primary features of Huntington’s disease is the degeneration of neurons in the caudate nucleus, putamen, and cerebral cortex.
The symptoms of Huntington’s disease are mostly the opposite of Parkinson’s disease symptoms. A person with Huntington’s disease may experience continuous, involuntary, and jerky movements.
To make smooth movements, there needs to be a balance between facilitating and inhibiting movement. But in people with Huntington’s disease, the basal ganglia circuits break down, which makes it difficult for the basal ganglia to control other parts of the brain.
Tourette syndrome is a neurological condition that causes rapid, repetitive movements or unwanted sounds called “tics.” You cannot easily control the unwanted movements and vocal sounds, but sometimes, you can partially suppress them.
Tourette syndrome involves a dysfunction of the basal ganglia, which causes an excess of the dopamine neurotransmitter.
Some common motor tics in Tourette syndrome include:
- obscene gesturing
- head jerking
- eye darting
- shoulder shrugging
- mouth movements
Some common vocal tics in Tourette syndrome include:
- clearing the throat
- using swear words
- repeating words or phrases
Dystonia is a condition that involves involuntary, persistent muscle contractions, causing atypical postures in certain parts of the body, such as the neck, hands, or toes. It is the third most common condition that affects movement.
Dystonia involves dopamine abnormalities and impaired inhibition of the striatum, both indicating that the basal ganglia play a role in the condition. While experts consider it a disorder of the basal ganglia, some studies suggest that other parts of the brain, such as the cerebellum, may also play a role in its development.
The basal ganglia are a cluster of nuclei in the brain’s center, close to the base. They interconnect, forming networks of structures that perform important roles.
The primary function of the basal ganglia is to help the brain control voluntary movements. The basal ganglia are also involved in the brain’s processes, such as rewards, emotions, addictions, motivations, and habits. This is why damage to the basal ganglia can affect different aspects of life, including movement, behavior, and cognitive function.