The three main basal ganglia targets are the pallidum, thalamus, and STN and each has been lesioned unilaterally and bilaterally. In considering the results from different reports, it should be emphasized that the methods of clinical assessment, site of lesion, method of target localization, and method of target confirmation have varied widely among centers. These factors may account for the differences in clinical outcomes across centers. The most comprehensive assessment would include:
1. Pre- and postoperative rating scales, such as the Unified Parkinson's Disease Rating Scale (UPDRS), Hoehn and Yahr, timed motor tests (25,26), dyskinesia rating scale (40), and cognitive and psychiatric assessments.
2. Identification of the anatomical target by CT, MRI, or CT-MRI fusion.
3. Identification of the physiological target. Some centers use microelectrode recordings, whereas others rely on macro-stimulation to check for adverse effects, which most commonly manifest as contraction of the face, arm or foot, sensory changes, ocular deviations, phosphenes, or speech arrest.
4. Verification of lesion size and location postoperatively by volumetric stereotaxic MRI.
5. Long-term follow-up.
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