Discharge patterns in the subtralamic nucleus and substantia nigra during deep brain stimulator implants

8 patients affected by Parkinson´s disease underwent implantation of stimulating electrodes in both subthalamic nuclei (STN). The stereotactic track was explored by a 1 MΩ microelectrode and recordings were taken at different depths, from 5 mm before down to 5 mm beyond the target, with a 1 mm step. At rest, in 8 out of the 16 successful tracks, spikes were recognizable in correspondence to the STN and in 2 in correspondence to the substantia nigra (SN) beyond the target. Spikes were detected by a matched filtering and threshold algorithm. The spike shape was analyzed by the rise time (0.199±0.064 msec, mean±SD, in the STN), decay time (0.345±0.114 msec) and bandwidth (1.612±0.622 kHz, -3 dB). The discharge patterns were analyzed through the inter spike interval (ISI) histogram, the conditional intensity function (CIF) and the spectrum of counts. The mean interval was 33.3±11.9 msec. Apart a single case of rhythmicity (1.65 Hz), the discharge pattern in the STN was always Poisson like with or without the presence of short bursts, as revealed by a flat CIF. Rhythmic patterns were found in SN.