Failure of single-unit neuronal activity to differentiate globus pallidus internus and externus in Parkinson disease

Object. The authors examine the validity of single-unit neuronal recordings as a method of differentiating the globus pallidus intemus (GPi) from the GP externus (GPe) in Parkinson Disease. Methods. One hundred twenty-eight recordings of apparent single-unit activity used to help guide final electrode placement in eight patients who underwent pallidotomy were analyzed using sophisticated spike sorting methods, and 185 neurons were characterized for mean firing frequency and percent of firing within bursts. In addition, the total spectral power was calculated on the full measured waveform for each of 128 samples without spike sorting. No correlation was identified between these measures of neuronal activity and depth within the GP. Conclusions. These results call into question the validity of relying on single-unit activity and microelectrode recordings in the operating room to localize lesion or electrode placement within the GPi during stereotactic pallidal surgery.