Diseases of the Basal Ganglia

As with brain research generally, much of what is known about the basal ganglia comes from studying diseases which affect them. This section briefly outlines the range of diseases which are caused by damage to the basal ganglia.

Damage to both the basal ganglia and the supplementary motor area are correlated with impaired performance on sequential tasks [6].

The ``theme'' of diseases affecting the basal ganglia appears to be that the balance between the two major pathways is disturbed: the result is either involuntary movements or impairments to motion.

According to Kandel et al. [32], the impaired motions include ``lack of movement (akinesia), slowness of movement (bradykinesia), and the shuffling gait of Parkinson's disease.''

The list of involuntary movements includes

tremors (rhythmic, involuntary, oscillatory movements), athetosis (slow, writhing movements of the fingers and hands, and sometimes of the toes), chorea (abrupt movements of the limbs and facial muscles), ballism (violent, flailing movements), and dystonia (a persistent posture of a body part which can result in grotesque movements and distorted positions of the body).

The major diseases of the basal ganglia are [32]:

Parkinson's disease

is related to a reduction of dopamine in the brain and damage to the dopaminergic pathway from the substantia nigra to the striatum. The result is an increased output of the basal ganglia to the thalamus. The major symptoms are tremor, rigidity, and akinesia.

Huntington's disease

is caused by a loss of specific striatal neurons. The result is a decreased output of the basal ganglia to the thalamus (as opposed to the increased output due to Parkinson's). As one might expect from their opposing neural behavior, Huntington's disease results in hyperkineticity, the opposite of the hypokineticity of PD.

Ballism

is tied to damage to the subthalamic nucleus. It causes severe involuntary movements, which tend to slowly diminish.

Tardive dyskinesia

is related to changes in the dopaminergic receptors, causing hypersensitivity to dopamine. It causes abnormal involuntary movements, particularly of the face and tongue.