Basal ganglia disease is a group of physical problems that occur when the group of nuclei in the brain known as the basal ganglia fail to properly suppress unwanted movements or to properly prime upper motor neuron circuits to initiate motor function. Research indicates that increased output of the basal ganglia inhibits thalamocortical projection neurons. Proper activation or deactivation of these neurons is an integral component for proper movement. If something causes too much basal ganglia output, then the ventral anterior (VA) and ventral lateral (VL) thalamocortical projection neurons become too inhibited, and one cannot initiate voluntary movement. These disorders are known as hypokinetic disorders. However, a disorder leading to abnormally low output of the basal ganglia leads to reduced inhibition, and thus excitation, of the thalamocortical projection neurons (VA and VL) which synapse onto the cortex. This situation leads to an inability to suppress unwanted movements. These disorders are known as hyperkinetic disorders.
Reasons for abnormal increases or decreases of basal ganglia output are not yet well understood. One possible factor could be the natural accumulation of iron in the basal ganglia, causing neurodegeneration due to its involvement in toxic, free-radical reactions. Though motor disorders are the most common associated with the basal ganglia, recent research shows that basal ganglia disorders can lead to other dysfunctions such as obsessive–compulsive disorder (OCD) and Tourette syndrome.
