Multiple-cell spike density and neural noise level analysis by semimicroelectrode recording for identification of the subthalamic nucleus during surgery for Parkinson's disease

Objective.   For targeting the subthalamic nucleus (STN), we attempted to quantify the changes in multiple cell activities by computing the neural noise level and multiple-cell spike density (MSD). Methods.   We analyzed the neural noise level and MSD by stepwise recording at every 0.25-mm increment during the final tracking in 90 sides of 45 patients with Parkinson's disease. The MSD was analyzed with cut-off levels ranging from 1.2- to 2.0-fold the neural noise level in the internal capsule or zona incerta in each trajectory. Results.   The dorsal boundary of the STN was identified from an increase in the neural noise ratio in all sides. The ventral boundary was identifiable, however, from a decrease in the neural noise ratio in only 70 sides (78%). In contrast, both the dorsal and ventral boundaries were clearly identified from an increase and a decrease in the MSD, respectively, in all of the 90 sides. Conclusion.   MSD analysis by semimicroelectrode recording represents a useful, practical, and apparently reliable means for identifying the boundaries of the STN.