[7] Ballism was defined by Meyers in 1968[8] as "Repetitive, but constantly varying, large amplitude involuntary movements of the proximal parts of the limbs.

[9] They are continuous and random and can involve proximal or distal muscles on one side of the body.

[10] Physicians can measure the severity of the disorder by having the patient perform a series of basic, predetermined tasks and counting the hemiballistic movements during a set time session.

[citation needed] The name hemiballismus literally means "half ballistic", referring to the violent, flailing movements observed on one side of the body.

[12] A stroke causes tissue to die due to a lack of oxygen resulting from an impaired blood supply.

[citation needed] This disease causes neuronal loss and gliosis, which can include the subthalamic nucleus and other areas of the brain.

It can be found primarily in the elderly and many of the reported cases have come from East Asian origin, which suggests that there may be some genetic disposition to development of hemiballismus as a result of hyperglycemia.

In patients with this type of hemiballismus, imaging reveals abnormalities in the putamen contralateral to the movements as well as the globus pallidus and caudate nucleus.

This decreases the conduction velocity of the neurons, making the signals received by the basal ganglia garbled and incomplete.

Due to the diverse nuclei that they contain, the basal ganglia are involved in numerous functions, including motor control.

[10] Injury to this area or its efferent or afferent connections can induce this disorder contralateral to the side of the lesion.

[10] From recent studies, it is now thought that hemiballismus can be associated with a decreased output of the globus pallidus.

In the case of hemiballismus, the opposite occurs, leading to the characteristic large, irregular movements.

[10] The putamen is also part of the basal ganglia and can be involved in hemiballismus due to the fact that it projects to the premotor cortex through the globus pallidus.

[6] The caudate nucleus is the portion of the basal ganglia that helps control voluntary movement.

Scientists are still unsure as to why this form of treatment works, as dopamine has not been directly linked to hemiballismus.

[10] An anticonvulsant called topiramate has helped patients in three cases and may be a viable treatment for the future.

[16] Intrathecal baclofen (ITB) therapy is used to treat a variety of movement disorders such as cerebral palsy and multiple sclerosis.

[5] In one case, before ITB the patient had an average of 10–12 ballism episodes of the right lower limb per hour.

After an ITB pump was implanted and the correct dosage was found, the frequency of ballistic right leg movements decreased to about three per day, and the right hip flexed to only 30 degrees.

In their experiments, several lesions were made in the basal ganglia structures in monkeys and then they monitored the results.

It was not until much later that this classical model began to expand to include other areas of the basal ganglia and even some cortical structures.

They also noticed that unlike human patients, the unusual movements in the monkeys were mainly in the lower extremities.

DeLong found that by using these chemicals, they could destroy only four percent of the subthalamic nucleus and still see hemiballistic movements.

This suggests that the subthalamic nucleus is plastic enough to adapt to small amounts of damage in order to resume normal function.