Putamen

The putamen is a large mass of gray matter located deep within each cerebral hemisphere. It is one of the major components of the basal ganglia and forms the lateral portion of the lentiform nucleus. Functionally and developmentally, however, the putamen is more closely associated with the caudate nucleus. Together, the putamen and caudate nucleus form the striatum.

The putamen serves as one of the principal input regions of the basal ganglia. It receives extensive excitatory projections from the cerebral cortex, particularly sensorimotor cortical areas, as well as modulatory dopaminergic input from the substantia nigra pars compacta. Its principal projection neurons are inhibitory GABAergic medium spiny neurons.

Through direct and indirect basal ganglia pathways, the putamen influences the globus pallidus, substantia nigra, thalamus, and ultimately the cerebral cortex. These circuits contribute particularly to movement regulation, action selection, motor learning, and the development and execution of learned motor behaviors.

Location

The putamen lies deep within the cerebral hemisphere, lateral to the globus pallidus and internal capsule.

It forms the lateral part of the lentiform nucleus and is separated from the cerebral cortex by several layers of white and gray matter.

In sectional anatomy, the putamen is readily identified as a large gray matter structure lateral to the globus pallidus.

General Features

Feature	Description
Location	Deep cerebral hemisphere
Basal ganglia grouping	Part of the striatum
Anatomical grouping	Lateral part of the lentiform nucleus
Medial neighbor	Globus pallidus
Functional partner	Caudate nucleus
Principal projection neurons	Medium spiny neurons
Principal projection neurotransmitter	GABA
Major role	Sensorimotor processing within basal ganglia circuits

Shape and Gross Anatomy

The putamen is a relatively large, rounded or shell-shaped collection of gray matter.

On coronal sections it forms the broad lateral component of the lentiform nucleus. Its lateral surface is convex, while its medial surface lies adjacent to the globus pallidus.

Unlike the caudate nucleus, the putamen does not have a prominent head, body, and tail division.

Lentiform Nucleus

The lentiform nucleus is an anatomical grouping consisting of the putamen and globus pallidus.

From lateral to medial, its major components are the putamen, external globus pallidus, and internal globus pallidus.

The term lentiform nucleus describes their combined appearance in sectional anatomy but does not imply that all of these structures have identical functional connections.

Relationship to the Globus Pallidus

The globus pallidus lies immediately medial to the putamen.

A thin layer of myelinated fibers known as the lateral medullary lamina separates the putamen from the external globus pallidus.

The putamen sends extensive inhibitory projections to both external and internal pallidal regions as part of basal ganglia circuitry.

Relationship to the Internal Capsule

The internal capsule lies medial to the lentiform nucleus.

It separates the putamen and globus pallidus from the caudate nucleus and thalamus across much of their extent.

Despite this white matter separation, bridges of gray matter connect the putamen with the caudate nucleus across the internal capsule.

Relationship to the Caudate Nucleus

The caudate nucleus and putamen are separated through much of their extent by fibers of the internal capsule.

Numerous strands of gray matter nevertheless extend between them, producing the striped appearance responsible for the term striatum.

Anteriorly and ventrally, the distinction between the caudate and putamen becomes less pronounced as they become continuous.

Striatum

The striatum consists principally of the caudate nucleus and putamen, with ventral regions including the nucleus accumbens commonly included within the ventral striatum.

It represents the major input component of the basal ganglia.

Extensive cortical, thalamic, and dopaminergic inputs converge on striatal neurons before information is transmitted to other basal ganglia structures.

Putamen versus Caudate Nucleus

Feature	Putamen	Caudate Nucleus
Shape	Compact, rounded mass	C-shaped structure
Major anatomical relationship	Lateral to globus pallidus	Closely follows lateral ventricle
Functional grouping	Striatum	Striatum
Prominent cortical association	Sensorimotor cortex	Association and prefrontal cortex
Major role	Prominent sensorimotor processing	Prominent associative and cognitive processing

Relationship to the Claustrum

The claustrum is a thin sheet of gray matter located lateral to the putamen.

The external capsule separates the putamen from the claustrum.

The extreme capsule lies lateral to the claustrum and separates it from the insular cortex.

Relationship to the Insular Cortex

The insular cortex lies lateral to the putamen but is separated from it by several intervening structures.

From medial to lateral, the sequence is approximately putamen → external capsule → claustrum → extreme capsule → insular cortex.

This arrangement is a useful landmark in coronal and axial neuroanatomy.

External Capsule

The external capsule is a thin sheet of white matter situated between the putamen medially and claustrum laterally.

It contains association and corticofugal fibers passing through the deep cerebral hemisphere.

Its position provides a clear anatomical boundary along much of the lateral surface of the putamen.

Ventral Continuity

Anteriorly and inferiorly, the putamen becomes continuous with ventral portions of the striatum.

In this region, the clear separation between caudate nucleus and putamen seen around the internal capsule diminishes.

This ventral continuity is important for understanding the organization of motor, associative, and limbic striatal territories.

Nucleus Accumbens

The nucleus accumbens occupies the ventral region near the junction between the caudate nucleus and putamen.

It forms an important component of the ventral striatum and participates prominently in reward, reinforcement, motivation, and goal-directed behavior.

The dorsal putamen, in contrast, is more strongly associated with sensorimotor basal ganglia circuits.

Microscopic Organization

The cellular organization of the putamen resembles that of other regions of the striatum.

Its dominant neuronal population consists of medium spiny projection neurons, accompanied by several types of interneurons.

These neurons receive convergent cortical, thalamic, and dopaminergic inputs and transmit processed information toward pallidal and nigral structures.

Medium Spiny Neurons

Medium spiny neurons constitute the great majority of striatal projection neurons.

Their dendrites contain numerous spines that receive excitatory synaptic input, particularly from the cerebral cortex and thalamus.

Their axons use GABA and therefore inhibit their principal basal ganglia targets.

Striatal Interneurons

The putamen also contains several populations of interneurons that regulate the activity of medium spiny neurons and local striatal networks.

These include cholinergic interneurons and several classes of GABAergic interneurons.

Although much less numerous than medium spiny neurons, interneurons can exert powerful influences on striatal processing.

Neurotransmitters

The principal output neurotransmitter of the putamen is GABA.

Glutamate provides major excitatory input from the cerebral cortex and thalamus, while dopamine from the substantia nigra pars compacta modulates striatal neuronal activity.

Acetylcholine and several neuropeptides also participate in local and projection signaling.

Corticostriatal Input

The putamen receives extensive corticostriatal projections from the cerebral cortex.

These fibers are predominantly glutamatergic and excitatory.

Motor, premotor, supplementary motor, and somatosensory cortical areas provide particularly important input to sensorimotor regions of the putamen.

Motor Cortex Connections

The motor cortex sends substantial projections to the putamen.

These connections allow information concerning intended and ongoing movements to enter basal ganglia circuits.

Basal ganglia processing subsequently influences motor cortical activity through pallidal, thalamic, and cortical pathways.

Premotor Connections

Premotor and supplementary motor cortical areas also project extensively to the putamen.

These connections contribute information related to motor planning, sequencing, internally generated movements, and preparation for action.

The putamen integrates these signals with sensory, contextual, and dopaminergic information.

Somatosensory Connections

Somatosensory cortical areas provide input to corresponding regions of the putamen.

This sensory information contributes to basal ganglia processing related to movement and action selection.

The convergence of motor and somatosensory signals allows the putamen to participate in sensorimotor integration.

Thalamostriatal Input

The putamen receives excitatory projections from several thalamic nuclei.

Thalamostriatal pathways provide information that complements cortical input and participates in regulating striatal activity.

These connections contribute to recurrent communication among the cortex, basal ganglia, and thalamus.

Nigrostriatal Pathway

The nigrostriatal pathway consists of dopaminergic fibers arising primarily from the substantia nigra pars compacta and projecting to the dorsal striatum.

The putamen receives particularly important dopaminergic input through this pathway.

Dopamine modifies the excitability and synaptic properties of striatal neurons and is essential for normal basal ganglia motor function.

Direct Pathway Neurons

A major population of putaminal medium spiny neurons participates in the direct basal ganglia pathway.

These neurons project inhibitory fibers toward the internal globus pallidus and substantia nigra pars reticulata.

They characteristically express D1-type dopamine receptors and contain neuropeptides including substance P and dynorphin.

Indirect Pathway Neurons

Another major population of medium spiny neurons participates in the indirect pathway.

These neurons project predominantly to the external globus pallidus.

They characteristically express D2-type dopamine receptors and are commonly associated with enkephalin-containing projections.

Direct Pathway

A simplified direct pathway is:

Cerebral cortex → putamen → GPi/SNr → thalamus → cerebral cortex.

Cortical excitation activates direct-pathway striatal neurons, which inhibit the GPi and substantia nigra pars reticulata.

This reduces inhibitory basal ganglia output toward selected downstream targets.

Direct Pathway Function

The GPi normally exerts tonic inhibitory influence on motor-related thalamic nuclei.

Inhibition of selected GPi neurons by direct-pathway striatal neurons reduces this inhibitory output.

Disinhibition of corresponding thalamic channels can facilitate cortical activity associated with an intended action.

Indirect Pathway

A simplified indirect pathway is:

Cerebral cortex → putamen → GPe → subthalamic nucleus → GPi/SNr → thalamus → cerebral cortex.

Activation of indirect-pathway neurons inhibits the external globus pallidus, which reduces its inhibitory influence on the subthalamic nucleus.

The resulting increase in subthalamic activity excites basal ganglia output nuclei.

Indirect Pathway Function

Increased activity of the GPi and substantia nigra pars reticulata strengthens inhibition of selected thalamic and brainstem targets.

This pathway contributes to suppression of competing or inappropriate actions.

Normal behavior depends on coordinated activity across direct, indirect, hyperdirect, and other interconnected basal ganglia networks.

Direct and Indirect Pathways

Feature	Direct Pathway	Indirect Pathway
Initial striatal target	GPi/SNr	GPe
Typical dopamine receptor	D1	D2
Striatal output	GABAergic	GABAergic
Classical functional effect	Facilitates selected actions	Suppresses competing actions

Dopamine and the Putamen

Dopamine is a major modulator of putaminal function.

Dopamine acting at D1 receptors generally facilitates direct-pathway activity, while dopamine acting at D2 receptors generally reduces indirect-pathway activity.

The combined effect promotes an appropriate balance between facilitation and suppression within basal ganglia motor circuits.

Functional Territories

The putamen is functionally organized rather than operating as a homogeneous structure.

Different regions receive input from different cortical territories and participate in corresponding basal ganglia loops.

The dorsal and posterior putamen are particularly associated with sensorimotor processing, while more anterior and ventral regions participate increasingly in associative and limbic functions.

Somatotopic Organization

Sensorimotor portions of the putamen exhibit somatotopic organization.

Different neuronal populations are associated with movements involving different body regions.

This organization reflects the patterned cortical input received by the striatum and continues through downstream basal ganglia circuits.

Motor Function

The putamen is strongly associated with motor processing within the basal ganglia.

It receives information from cortical motor areas and transmits processed inhibitory output into pallidal and nigral pathways.

Through these circuits, it contributes to selecting, scaling, sequencing, initiating, and suppressing movements.

Action Selection

The putamen contributes to action selection by helping determine which motor programs should be facilitated and which competing programs should be suppressed.

Different striatal neuronal populations influence basal ganglia output through partially distinct pathways.

This organization allows multiple potential actions to be evaluated and regulated in parallel.

Motor Learning

The putamen participates in the acquisition and refinement of learned motor behaviors.

Repeated practice can alter corticostriatal synaptic activity and the way basal ganglia circuits respond to particular sensory and motor contexts.

Dopaminergic signaling contributes importantly to this form of striatal plasticity.

Habit Learning

Dorsal striatal circuits, including the putamen, participate in the development and execution of habitual behaviors.

As behaviors become extensively practiced, their control can become increasingly dependent on stimulus-response associations and established motor patterns.

The putamen is particularly associated with the sensorimotor components of these learned behaviors.

Procedural Learning

The putamen contributes to forms of procedural learning involving acquisition of skills and repeated action sequences.

Its connections with motor and premotor cortical areas allow learned patterns to be integrated into efficient motor performance.

These functions operate together with cerebellar and cortical learning systems.

Sensorimotor Integration

The convergence of motor and somatosensory cortical input allows the putamen to integrate information about intended movement with information related to the state of the body.

This integration helps basal ganglia circuits regulate actions according to ongoing sensory and motor conditions.

The putamen therefore functions as part of a distributed sensorimotor network rather than as an isolated motor nucleus.

Blood Supply

The putamen receives arterial blood predominantly from penetrating branches of the middle cerebral artery, particularly the lenticulostriate arteries.

Additional contributions can arise from neighboring deep arterial territories.

Because the putamen is supplied by small penetrating vessels, it is a common site of deep cerebral vascular lesions.

Lenticulostriate Arteries

The lenticulostriate arteries are small perforating branches arising mainly from the middle cerebral artery.

They enter through the anterior perforated substance and supply the putamen, portions of the caudate nucleus and globus pallidus, and parts of the internal capsule.

Their small caliber and penetrating course make them clinically important in hypertensive small-vessel disease.

Venous Drainage

Venous blood from the putamen drains through deep cerebral venous pathways.

Small veins draining the basal ganglia communicate with deeper venous channels around the ventricular and thalamic regions.

These ultimately contribute to the internal cerebral veins and related deep venous structures.

Clinical Significance

Parkinson Disease

The putamen is functionally central to the pathophysiology of Parkinson disease.

Degeneration of dopaminergic neurons in the substantia nigra pars compacta causes a marked reduction in dopamine reaching the dorsal striatum, with the putamen particularly affected functionally.

The resulting imbalance in basal ganglia pathways contributes to bradykinesia, rigidity, and other motor manifestations.

Nigrostriatal Dopamine Loss

Loss of nigrostriatal dopamine alters activity in both direct and indirect pathway neurons.

Reduced D1-mediated facilitation decreases direct-pathway influence, while reduced D2-mediated modulation increases the relative influence of indirect-pathway activity.

These changes increase inhibitory basal ganglia output and reduce facilitation of selected motor programs.

Huntington Disease

Huntington disease causes progressive degeneration of striatal neurons involving both the caudate nucleus and putamen.

Early degeneration disproportionately affects neuronal populations associated with the indirect pathway, contributing to choreiform movements.

As degeneration progresses, additional striatal populations and broader neural systems become involved.

Dystonia

Abnormal activity within putaminal and broader basal ganglia circuits can contribute to dystonia.

Disturbances in sensorimotor integration, plasticity, and action selection may contribute to sustained or intermittent abnormal muscle contractions and postures.

Dystonia reflects network dysfunction and is not attributable to the putamen alone.

Putaminal Hemorrhage

The putamen is an important site of deep intracerebral hemorrhage, particularly in association with chronic hypertension and disease of small penetrating arteries.

A hemorrhage may remain centered within the putamen or extend into the internal capsule, globus pallidus, ventricular system, or surrounding white matter.

Clinical deficits depend strongly on the size and direction of extension.

Internal Capsule Involvement

Because the internal capsule lies immediately medial to the lentiform nucleus, a putaminal hemorrhage or infarction can extend into major projection fibers.

Damage to corticospinal and corticobulbar pathways can produce substantial contralateral motor deficits.

Associated sensory deficits may occur when neighboring sensory pathways are involved.

Putaminal Infarction

Occlusion of penetrating arteries can produce ischemic lesions involving the putamen.

Small infarcts may be confined to portions of the basal ganglia, while larger lesions may involve the internal capsule and neighboring structures.

Clinical manifestations vary according to the exact anatomical distribution of injury.

Wilson Disease

The putamen and other basal ganglia structures can be affected in Wilson disease, a disorder of copper metabolism.

Neurological involvement may produce movement abnormalities, dysarthria, dystonia, tremor, and behavioral or psychiatric manifestations.

Structural and signal abnormalities involving the putamen may be visible on MRI.

Hypoxic and Metabolic Injury

The putamen can be affected by certain hypoxic, toxic, and metabolic disorders.

Because deep gray matter structures have substantial metabolic requirements, some systemic insults produce bilateral basal ganglia abnormalities.

The precise distribution varies according to the underlying mechanism.

Neuroimaging

The putamen is readily identified on CT and MRI.

On axial and coronal images, it lies lateral to the globus pallidus and medial to the external capsule and claustrum.

Its relationships with these structures, the internal capsule, and caudate nucleus make it an important landmark in sectional neuroanatomy.

Sectional Anatomy

In a typical coronal section through the basal ganglia, the putamen forms the lateral portion of the lentiform nucleus.

A useful medial-to-lateral sequence is internal capsule → globus pallidus → putamen → external capsule → claustrum → extreme capsule → insular cortex.

Recognition of this sequence helps distinguish the putamen from neighboring gray and white matter structures.

Developmental Anatomy

The putamen develops as part of the striatal component of the basal telencephalon.

It shares developmental and functional relationships with the caudate nucleus.

As fibers of the internal capsule grow through the developing striatal region, they separate much of the caudate from the putamen while leaving bridges of gray matter between them.

Anatomical Variation

The size and exact contour of the putamen vary among individuals.

Its fundamental relationships with the globus pallidus, internal capsule, external capsule, and claustrum remain relatively consistent.

Its arterial supply can vary because penetrating vascular territories overlap within the basal ganglia.

Functional Importance

The putamen is a major input structure of the basal ganglia and is particularly important in sensorimotor basal ganglia circuits. It receives extensive information from motor, premotor, supplementary motor, and somatosensory cortical regions and integrates these signals with thalamic and dopaminergic input.

Through its GABAergic projections into direct and indirect basal ganglia pathways, the putamen influences pallidal and nigral output and ultimately modifies thalamocortical and brainstem activity.

The putamen therefore contributes to movement regulation, action selection, sensorimotor integration, motor learning, procedural learning, habit formation, and the execution of learned motor behaviors.