FUNCTIONAL-ANATOMY OF THE PALLIDAL BASE IN PARKINSONS-DISEASE

OBJECTIVE: The purpose of this study is to define the morphology of th e boundary between the globus pallidus and the ansa lenticularis (i.e. , pallidal base) in humans. This information is important for surgeons who perform pallidotomy. METHODS: Thirty-eight patients with Parkinso n's disease underwent pallidotomy using microrecording techniques. The pallidal base was identified by the loss of neuronal single unit acti vity and by the change in background noise, as analyzed on the audio m onitor and by fast Fourier transformation. RESULTS: Three quarters of the patients had an abrupt transition of the background noise from neu ronal to axonal activity. One quarter of the patients had multiple suc cessive transitions of the background activity, over a distance of 0.4 to 2 mm (median, 1 mm). CONCLUSION: We conclude that the pallidal bas e is not a smooth, sharp boundary between the globus pallidus and the ansa lenticularis. We propose two models that define the morphology of the pallidal base. One model depicts the pallidal base as a multifold ed boundary that distinctly separates pallidal neurons from ansa lenti cularis axons. Another model depicts the pallidal base as an indistinc t transitional boundary between the globus pallidus and the ansa lenti cularis, which contains axonal fibers intermixed with small clusters o f pallidal neurons. We discuss the clinical relevance of these finding s.