The putamen is a rounded structure located deep within the cerebral hemispheres, forming part of the brain’s basal ganglia. It plays a role in various functions, including motor control and different types of learning. This subcortical nucleus is a component in neural networks, influencing brain activity.
Precise Anatomical Placement
The putamen is situated at the base of the forebrain, positioned above the midbrain. It has a rounded, somewhat shell-like shape, making it the most lateral of the basal ganglia nuclei when viewed in a cross-section of the brain. This paired structure exists bilaterally.
Together with the caudate nucleus, the putamen forms the dorsal striatum. The internal capsule, a large fiber tract, passes through the middle, effectively dividing the dorsal striatum into these two distinct parts. The putamen also combines with the globus pallidus to form the lentiform nucleus, which has a lens-like appearance.
The putamen’s immediate neighbors include the globus pallidus, which lies medially to it, and the external capsule, located laterally. This positioning places the putamen in a central hub, allowing it to receive input from various regions of the cerebral cortex. It also connects to other structures like the substantia nigra, the claustrum, and the thalamus.
How Its Location Influences Its Functions
The putamen’s deep and interconnected location within the basal ganglia network influences its functional roles, particularly in motor control, learning, and habit formation. As part of the dorsal striatum, it serves as an input nucleus, receiving information primarily from the cerebral cortex and, to a lesser extent, the thalamus. This position allows it to integrate signals from sensory and motor cortical areas, acting as a gateway to the basal ganglia.
Its connections to the substantia nigra, specifically the substantia nigra pars compacta, are important. This region releases dopamine to the dorsal striatum, which modulates movement. The putamen’s involvement in both direct and indirect pathways of the basal ganglia, which either promote or inhibit movement, is enabled by its receipt of this dopaminergic input. This allows the putamen to contribute to movement preparation and execution, and influence their vigor based on motivational factors.
The putamen’s role in cortico-striatal loops, which are responsible for emotions, cognition, and sensorimotor functions, highlights the influence of its location. Its participation in these loops facilitates implicit learning and habit formation, where it processes feedback to update behavioral strategies. The anterior part of the putamen is involved in movement preparation, while the posterior putamen plays a role in execution, demonstrating functional specialization.
Clinical Implications of Putamen Location
Due to its specific location and interconnectedness, the putamen is susceptible to damage in various neurological conditions, leading to clinical consequences. In Parkinson’s disease, for example, there is a loss of dopaminergic neurons in the substantia nigra pars compacta, which directly projects to the putamen. This dopamine depletion, particularly in the dorsal and intermediate areas of the putamen, disrupts motor control and leads to characteristic symptoms like tremors and slowed movement.
Huntington’s disease also affects the putamen, causing degeneration of cells within the basal ganglia, including those that secrete inhibitory neurotransmitters like GABA. This loss results in uncontrolled, involuntary movements, often described as chorea, highlighting how damage to this region impacts motor coordination. The putamen’s vulnerability makes it important in the pathology of these neurodegenerative disorders.
Stroke can also impact the putamen due to its vascular supply from the lenticulostriate arteries. Small putaminal strokes can lead to a range of symptoms, including mixed motor and sensory deficits, pure motor or sensory impairments, ataxic hemiparesis, or dysarthria with clumsy hands. Rare cases of bilateral putaminal hemorrhages can occur due to bleeding disorders or other conditions, showing its vulnerability.