The basal ganglia are a group of interconnected structures deep inside the brain that help control movement, learn habits, select actions, and adjust behavior based on experience. They do not directly command muscles. Instead, they work with the cerebral cortex, thalamus, and other brain regions to influence which actions are initiated, how smoothly movements unfold, and which behaviors become easier to perform through repetition.
These circuits are important for far more than physical movement. They also contribute to reward learning, motivation, decision-making, and the formation of habits. When basal ganglia circuits malfunction, the effects can range from difficulty initiating movement to involuntary motions, repetitive behaviors, and changes in motivation.
What are the basal ganglia?
The basal ganglia are a collection of interconnected clusters of neurons, or nerve cells, located deep within the cerebral hemispheres. Although the word ganglia traditionally refers to collections of nerve cell bodies outside the brain and spinal cord, the term basal ganglia is the established name for these structures within the brain.
The major components of the basal ganglia include the striatum, globus pallidus, subthalamic nucleus, and substantia nigra. Together, they form circuits that process information from different parts of the brain and influence the activity of networks responsible for movement and behavior.
The striatum is the principal entry point for much of the information entering the basal ganglia from the cerebral cortex. It includes the caudate nucleus and putamen, which receive signals from different cortical regions and participate in partially distinct but interconnected functions.
The globus pallidus has internal and external divisions, known as the internal segment and external segment. These divisions help regulate activity within basal ganglia circuits. The subthalamic nucleus is another important component, contributing to the control of movement and the suppression of competing actions.
The substantia nigra, located in the midbrain, contains two functionally distinct regions. The substantia nigra pars compacta produces dopamine, a chemical messenger that helps regulate learning and action selection. The substantia nigra pars reticulata is an important output structure that helps control activity in other brain regions.
The nucleus accumbens, part of the ventral striatum, is especially involved in motivation, reward processing, and reinforcement learning. Its connections help link experiences with the likelihood of repeating particular actions.
These structures do not operate independently. Their functions emerge from the patterns of connections among them and their communication with other parts of the brain.
How the basal ganglia control movement
The basal ganglia help determine which movements are carried out, which are held back, and how actions are adjusted to suit a person’s goals. Their influence depends on circuits that connect the cerebral cortex to the basal ganglia and then back toward the cortex through the thalamus.
A simplified description of this process begins in the cerebral cortex, where information about goals, sensory input, and possible actions is processed. The cortex sends signals to the striatum, which integrates these inputs with information influenced by dopamine and other neural signals.
The basal ganglia then process this information through interconnected pathways. Their output affects the thalamus and brainstem, which in turn influence cortical activity and motor systems. The resulting changes help shape the initiation and execution of movement.
This arrangement allows the brain to select an appropriate action without activating every possible movement at once. For example, reaching for a cup requires coordinated activity across multiple muscle groups, while unrelated movements must be limited enough to allow the intended action to proceed.
The basal ganglia help regulate this balance between facilitating desired actions and suppressing competing ones. They also contribute to movement vigor, the speed and intensity with which an action is performed, and the ability to adjust behavior when circumstances change.
However, the basal ganglia are not the sole controllers of movement. The motor cortex helps generate commands for voluntary movement, the cerebellum contributes to coordination and error correction, and the spinal cord carries signals to muscles and organizes many movement-related reflexes. Effective movement depends on cooperation among these systems.
The direct and indirect pathways
Two major pathways through the basal ganglia, called the direct and indirect pathways, are central to understanding how these circuits regulate movement. A third pathway, the hyperdirect pathway, provides an additional route for rapidly influencing basal ganglia output.
These pathways are not simple on-and-off switches. They operate simultaneously, interact with one another, and help shape action selection through changes in neural activity.
The direct pathway facilitates selected actions
In the direct pathway, neurons in the striatum send inhibitory signals to output regions of the basal ganglia, particularly the internal segment of the globus pallidus and the substantia nigra pars reticulata.
Under typical conditions, these output regions continuously inhibit parts of the thalamus and other targets. When the direct pathway becomes more active, it reduces that inhibition. This process is called disinhibition.
The thalamus can then provide stronger excitatory input to relevant areas of the cerebral cortex, helping facilitate the selected action.
In practical terms, the direct pathway can make it easier for a particular movement or action to proceed. Its effects depend on which circuit is engaged and the wider pattern of activity in the network.
The indirect pathway helps suppress competing actions
The indirect pathway involves a more extended series of connections. Striatal neurons inhibit the external segment of the globus pallidus, which normally inhibits the subthalamic nucleus. Reducing this pallidal inhibition allows the subthalamic nucleus to become more active.
The subthalamic nucleus sends excitatory signals to the internal globus pallidus and substantia nigra pars reticulata. These output regions can then increase their inhibition of the thalamus and other targets.
This sequence can reduce the activity of cortical circuits associated with actions that should not proceed.
The indirect pathway therefore contributes to limiting unwanted or competing actions. Its role is more complex than simply stopping movement, however. It also participates in action selection, learning, and the adjustment of behavior as circumstances change.
The hyperdirect pathway supports rapid control
The hyperdirect pathway carries signals from the cerebral cortex directly to the subthalamic nucleus, bypassing the striatum. The subthalamic nucleus can rapidly increase the activity of basal ganglia output regions, strengthening inhibition of downstream targets.
This pathway is thought to help interrupt or restrain actions when rapid control is needed. For example, when a person begins an action but suddenly recognizes a reason to stop, hyperdirect circuit activity may contribute to the rapid adjustment.
The direct, indirect, and hyperdirect pathways work together rather than operating as isolated systems. The traditional distinction between a movement-promoting direct pathway and a movement-suppressing indirect pathway is useful for understanding their basic organization, but actual behavior depends on more dynamic interactions among many neural populations.
Why dopamine matters
Dopamine is a neurotransmitter, a chemical messenger that allows neurons to influence one another. In the basal ganglia, dopamine is particularly important for regulating the striatum and helping the brain learn which actions are worth repeating.
Most dopamine involved in these circuits is supplied by neurons in the substantia nigra pars compacta. These neurons project to the striatum, where dopamine modifies the responsiveness of different populations of neurons.
In a simplified model, dopamine tends to increase the responsiveness of striatal neurons associated with the direct pathway through D1-type dopamine receptors. It tends to reduce the responsiveness of many neurons associated with the indirect pathway through D2-type receptors. These effects help bias the system toward facilitating selected actions while adjusting the suppression of competing ones.
Dopamine does not simply produce movement or pleasure. Its effects depend on receptor type, neural circuit, timing, and the activity of other signaling systems.
Dopamine also contributes to reinforcement learning. When an outcome is better or worse than expected, changes in dopamine signaling can help update the value associated with an action or cue. These learning signals allow behavior to adapt to experience.
For example, if a particular action repeatedly produces a useful outcome, the brain can gradually become more likely to select it in similar circumstances. Dopamine helps update the connections and responses involved in this process.
When dopamine signaling is disrupted, both movement and learning can be affected. The consequences depend on which pathways are involved and how the disruption changes activity across the wider network.
How the basal ganglia help form habits
Habits are behaviors that become more automatic through repetition. They allow people to perform familiar actions with less deliberate attention, freeing mental resources for other tasks.
The basal ganglia, particularly the striatum, play an important role in habit learning. Through repeated experience, neural circuits learn relationships between situations, actions, and their consequences. Actions that initially require substantial conscious decision-making can gradually become easier to initiate in familiar contexts.
For example, someone learning to drive must consciously monitor steering, braking, mirrors, and traffic. With practice, many of these component actions become more automatic. The person can still adjust them deliberately, but familiar situations no longer require the same level of conscious attention.
The dorsal striatum, which includes the caudate nucleus and putamen, contributes to learning and controlling actions. In broad terms, the dorsomedial striatum is associated with goal-directed action and evaluating outcomes, while the dorsolateral striatum is more strongly associated with habitual control in many experimental settings. These divisions are not absolute, and their functions overlap.
Goal-directed behavior depends on an understanding of the relationship between an action and its outcome. A person chooses an action partly because they expect a particular result. Habitual behavior, by contrast, can be triggered more automatically by familiar cues and may continue even when the outcome has become less valuable.
These modes of control can coexist. A person might deliberately decide to go to the gym but follow a well-established sequence of actions once there. The overall goal is intentional, while many of the individual behaviors are habitual.
Habits are not inherently good or bad. Brushing teeth, checking mirrors before changing lanes, and following a familiar morning routine can all become efficient through repetition. The same learning mechanisms can also support unwanted behaviors, such as repeatedly checking a phone in response to notifications.
Habit formation is not controlled by the basal ganglia alone. The prefrontal cortex contributes to planning, monitoring, and deliberate control, while sensory and memory systems help identify the situations in which learned behaviors are likely to occur.
The basal ganglia, reward, and motivation
The basal ganglia help the brain learn from rewards, anticipate outcomes, and determine whether an action is worth the effort. These functions depend on circuits that connect the striatum with the prefrontal cortex, limbic regions involved in emotion, and dopamine-producing neurons.
The ventral striatum, including the nucleus accumbens, is particularly important in processing information related to reward and motivation. It helps integrate signals about expected outcomes, current needs, and the potential value of different actions.
Reward is not limited to pleasurable experiences. It can include food when hungry, social approval, progress toward a goal, or any outcome that strengthens the likelihood of repeating a behavior.
One important process is reward prediction error: the difference between an outcome and what was expected. When a reward is better than anticipated, dopamine signaling can change in ways that support learning. When an expected reward fails to occur, dopamine activity may decrease at particular moments. These signals help the brain revise its expectations.
Motivation also involves more than how rewarding an outcome seems. A person must evaluate whether the expected benefit justifies the effort, time, and possible risk. Basal ganglia circuits contribute to this evaluation and help translate motivational signals into action.
Disruptions in these circuits can therefore affect not only the ability to move but also the willingness or capacity to initiate goal-directed behavior. Such effects arise from interactions among the basal ganglia and broader networks involved in emotion, cognition, and motivation.
Other cognitive functions of the basal ganglia
Although the basal ganglia are often introduced as movement-control structures, they also participate in cognitive processes. Their connections with different regions of the cerebral cortex allow them to influence how people select responses, organize behavior, and adapt to changing circumstances.
Circuits linking the basal ganglia with the prefrontal cortex contribute to working memory, rule learning, planning, and cognitive flexibility. Working memory is the ability to hold and use information temporarily, while cognitive flexibility is the ability to change strategies or responses when circumstances change.
For instance, when a familiar rule no longer works, a person must recognize the change, suppress the old response, and select a more appropriate one. Basal ganglia circuits help regulate these processes by influencing which patterns of cortical activity are reinforced or inhibited.
The basal ganglia also participate in procedural learning, the gradual acquisition of skills through practice. Learning a sequence of keystrokes, refining a tennis serve, or developing a smooth sequence of hand movements involves several brain systems, including the basal ganglia and cerebellum. The basal ganglia contribute to selecting and reinforcing effective actions, while the cerebellum is especially important for timing, coordination, and error-based adjustments.
These functions illustrate a broader principle: the basal ganglia help regulate action in both physical and cognitive domains. Their role depends on the cortical and subcortical networks with which they communicate.
What happens when the basal ganglia malfunction?
Because the basal ganglia influence movement, learning, and behavior, dysfunction can produce a range of symptoms. Some conditions primarily affect movement, while others involve repetitive actions, changes in motivation, or difficulties with cognitive control.
The particular symptoms depend on the affected structures, the direction and extent of changes in neural activity, and the underlying cause.
Parkinson’s disease
Parkinson’s disease is a progressive neurological disorder strongly associated with the loss of dopamine-producing neurons in the substantia nigra pars compacta. As dopamine input to the striatum declines, basal ganglia circuits become less effective at regulating movement.
Common motor symptoms include bradykinesia, meaning slowness of movement, and rigidity, or increased resistance to passive movement. Many people also develop a resting tremor, although tremor does not occur in everyone.
People with Parkinson’s disease may have difficulty starting movements, reducing their natural arm swing while walking, or making rapid adjustments to ongoing actions. Their movements can become smaller and slower.
The disorder can also affect sleep, mood, cognition, and autonomic functions. These nonmotor symptoms reflect the fact that Parkinson’s disease affects more than the circuits responsible for voluntary movement.
Huntington’s disease
Huntington’s disease is an inherited neurodegenerative disorder caused by a pathogenic expansion in the HTT gene. It affects multiple brain regions, including the striatum, where neurons involved in basal ganglia circuits progressively deteriorate.
One characteristic feature is chorea, a pattern of involuntary, irregular movements that can appear to flow unpredictably from one body part to another. Some people also develop difficulties with voluntary movement, balance, and coordination.
Huntington’s disease can affect thinking, emotional regulation, and behavior as well. Changes in striatal and connected cortical circuits contribute to these symptoms, which may develop alongside or even before prominent motor problems.
Dystonia and other movement disorders
Dystonia involves sustained or intermittent muscle contractions that produce abnormal postures or repetitive twisting movements. It can affect a single body region or several parts of the body.
The basal ganglia are important in many forms of dystonia, although the condition can involve broader motor networks, and its causes vary. Not all dystonia results from a primary problem confined to the basal ganglia.
Other movement disorders, including some forms of tremor and tic disorders, also involve circuits connected to the basal ganglia. In Tourette syndrome, for example, altered activity in cortico-striato-thalamo-cortical networks is associated with motor and vocal tics. These conditions differ in their underlying mechanisms, and basal ganglia involvement does not mean they all share the same cause.
Obsessive-compulsive disorder and related behaviors
The basal ganglia also participate in circuits involved in evaluating thoughts, selecting responses, and regulating repetitive behavior. Changes in these networks have been implicated in obsessive-compulsive disorder (OCD).
OCD involves persistent, unwanted thoughts or urges, called obsessions, and repetitive behaviors or mental acts, called compulsions, that a person feels driven to perform. These symptoms cannot be explained by basal ganglia dysfunction alone. They arise from complex interactions among cortical, striatal, and other brain networks, alongside psychological and environmental factors.
The basal ganglia’s involvement helps explain why systems that normally support efficient, repeated actions may also be relevant to difficulties disengaging from certain thoughts or behaviors. However, habitual behavior, compulsions, and tics are distinct phenomena and should not be treated as interchangeable.
How scientists study the basal ganglia
Researchers use several methods to understand how basal ganglia circuits work in healthy brains and in neurological conditions.
Brain imaging, including functional magnetic resonance imaging, can identify changes in activity associated with movement, reward, learning, or decision-making. These measurements reveal patterns of activity across networks but do not, by themselves, establish that a particular structure causes a behavior.
Electrophysiological recordings measure electrical activity from individual neurons or groups of neurons. Such recordings can reveal how firing patterns change during action selection, movement, and learning. In some clinical settings, recordings from implanted electrodes also help researchers investigate abnormal circuit activity.
Studies of neurological disorders provide another source of evidence. When a particular population of neurons degenerates or a brain region is damaged, the resulting symptoms can reveal something about its normal function. However, because brain circuits are interconnected, the effects of damage may extend beyond the directly affected region.
Deep brain stimulation is used to treat selected movement disorders, particularly Parkinson’s disease, and some other conditions in carefully chosen cases. The treatment involves delivering electrical stimulation through implanted electrodes to specific brain targets or connected circuits. Its benefits show that modifying activity in these networks can improve symptoms, although the precise mechanisms of stimulation are complex and not fully understood.
Together, these approaches show that the basal ganglia are not simply a motor control center or a habit-forming mechanism. They are part of a set of interconnected brain circuits that help select actions, regulate movement, learn from consequences, and adapt behavior to changing goals and circumstances.
