The putamen is a large structure situated deep within the cerebral hemispheres, functioning as a foundational component of the basal ganglia. This collection of subcortical nuclei coordinates movement and behavior. The putamen plays a specialized role in the neural circuitry that governs how we initiate, execute, and refine physical actions. Its function also extends beyond simple motor control, influencing habit formation and various forms of learning.
Anatomical Placement and Structure
The putamen is nestled deep within the forebrain, situated bilaterally beneath the cerebral cortex. It is the largest structure within the basal ganglia system, which processes motor and non-motor information. The structure is shaped like a shell or crescent, forming the outermost portion of the deep brain nuclei.
The putamen joins with the globus pallidus to form the lentiform nucleus. The putamen forms the lateral, or outer, portion of this lens-shaped structure. Medially, it is separated from the globus pallidus by a thin layer of white matter called the lateral medullary lamina.
Functionally, the putamen and the caudate nucleus are linked, together forming the striatum. The striatum serves as the main entrance point for signals entering the basal ganglia from the cerebral cortex. Although the internal capsule separates the putamen from the caudate nucleus, bridges of gray matter cells cross this divide, giving the striatum a striped appearance. The putamen receives its blood supply primarily from the lenticulostriate arteries, which are small branches of the middle cerebral artery.
Core Roles in Movement and Learning
The putamen acts as the primary input station for motor control pathways within the basal ganglia. It receives extensive excitatory signals from nearly all areas of the cerebral cortex, especially the motor and somatosensory regions. This input allows the putamen to process the initial commands for movement. Its influence is directed toward regulating movements at every stage, from initial preparation to final execution.
A primary function involves facilitating desired movements while simultaneously suppressing unwanted movements. It is instrumental in scaling the amplitude and force of a movement, ensuring actions are appropriate for the task. For example, the putamen helps modulate the exact amount of muscle effort required to pick up a feather versus a heavy book.
Beyond immediate motor control, the putamen plays a significant role in procedural learning. This type of learning relates to the automatic acquisition of skills and habits that do not require conscious thought, such as riding a bicycle or tying a shoe. The putamen helps shift control of these repetitive, learned actions from conscious brain areas to the subconscious. This makes the movements more fluid and efficient over time by reinforcing specific movement patterns through repeated practice.
Putamen Dysfunction and Associated Diseases
When the putamen or its circuits are damaged, severe motor control deficits often manifest. The clearest example is Parkinson’s Disease (PD), which involves the progressive loss of dopamine-producing neurons in the substantia nigra. Since these neurons project directly to the striatum, their loss leads to a profound depletion of dopamine in the putamen. This lack of dopamine input impairs the putamen’s ability to modulate motor circuits, resulting in classic PD symptoms like resting tremor, muscle rigidity, and slowness of movement.
The structural integrity of the putamen is also compromised in other neurodegenerative conditions. In Huntington’s Disease (HD), the putamen and the caudate nucleus undergo significant atrophy and loss of neurons. This damage contributes to the involuntary, dance-like movements known as chorea that characterize the disease. Furthermore, the putamen’s role in habit formation links it to certain neuropsychiatric disorders, such as Obsessive-Compulsive Disorder (OCD) and addiction.