Which of the following stereotactic procedures would be performed primarily to alter the function of the brain?

C. Stereotactic radiofrequency lesion of the right ventrolateral thalamus for Parkinson's disease.

DISCUSSION: The biopsy of a lesion, radiotherapy treatment of an arteriovenous malformation, and excision of an arteriovenous malformation are all procedures for structural lesions of the brain that can be imaged by either CT or MRI. These structural lesions may or may not cause neurologic changes, but the treatment directed at them is intended principally to keep lesion-induced damage from increasing (for example, with the development of hemorrhage). On the other hand, the thalamus is expected to have a normal structural appearance and function in Parkinson's disease, when the neurochemical abnormality is located in the substantia nigra and the striatum (caudate and putamen). Thus, a lesion is made in the thalamus principally to affect the function of the brain, altering a normal component of one of the motor circuits to compensate for the changes in the other parts (i.e., the basal ganglia).