Basal Nuclei and Motor Control

Basal Nuclei (Basal Ganglia)

• Essential for movement control, mood regulation, and complex behaviors
• Older name: basal ganglia; however, this is inaccurate as basal nuclei are part of the CNS, unlike ganglia which are clusters outside the CNS.
• Six structures comprise the basal nuclei: four located in the forebrain (telencephalon), underneath the cortex and in front of the thalamus; and one in the midbrain, close to the other five.
• Receive dopamine from the substantia nigra of the midbrain.
• Dopamine deficiency (due to substantia nigra death) causes movement disorders (Parkinson's Disease).
• Parkinson's Disease may also be associated with mental disorders in approximately half of patients.
• Huntington's Disease, another degenerative basal nuclei disease, also causes mental disorders.
• Obsessive-compulsive disorder is linked to abnormalities in the caudate nucleus.

Basal Nuclei Motor Circuitry

• Extensive motor loops connect prefrontal cortex, premotor/ supplementary motor cortices (area 6), caudate, and putamen nuclei.
• Caudate and putamen output travels through the globus pallidus.
• Globus pallidus projects to ventral anterior and ventral lateral thalamus, which further project back to prefrontal cortex and area 6.
• Nigrostriatal pathway (substantia nigra to caudate and putamen) provides dopamine to regulate movement.
• Loss of these dopamine-producing cells causes Parkinson's Disease.
• Subthalamic nucleus, located beneath the thalamus, also modifies movement circuits within the basal nuclei.
• Damage to the subthalamic nucleus causes hemiballismus.

Basal Nuclei Function

• Primary function: initiating and executing movement.
• Role in action selection: choosing the appropriate movement from possible options, considering emotional aspects (reward/punishment).
• Asymmetry in caudate nucleus activity linked to obsessive-compulsive disorder.
• Parkinson's and Huntington's diseases present with both movement disorders and emotional disturbances.