Microelectrode recordings from Patients with Parkinson-Disease

Microelectrode guided implantations of deep brain stimulation (DBS) electrodes in the subthalamicus nucleus (STN) for treating advanced Parkinson's disease (PD) offer the possibility of studying the spontaneous discharge behavior of basal ganglia neurons in humans. This scientific benefit adds to the clinical value of microelectrode recordings in delineating the exact borders of STN and substantia nigra – thereby helping to identify the most effective place for the permanent stimulation electrodes. We used a Ben-Gun approach to simultaneously collect activity from 5 trajectories during implantation of STN-DBS electrodes. Multiunit activity was bandpass filtered (300–10.000Hz), amplified and digitally stored by use of a CED 1401 system. Recordings of 71 patients were screened and categorized according to the signal to noise ratio. Only recordings with stable spiking activity over a period of at least 30 seconds and without signs of injury potentials were further processed. A threshold detection and template matching procedure in combination with a principle component analysis were used to isolate single unit activity (SUA) offline (CED spike 2 software). SUA of 283 STN neurons could be isolated from 41 patients. Based on the shape of their inter-spike interval histograms 60% of these neurons exhibited a burst-like positively skewed firing pattern, 10% a burst-like bimodal, 9% a bursting narrow positively skewed pattern, 4% an irregular and 18% a tonic firing pattern. Oscillatory activity was a rare exception. The mean firing rates of the group of burst-like neurons ranged between 43 and 60Hz, the tonic neurons discharged at around 40Hz and the irregular ones at around 12Hz. Since enhanced neuronal synchrony in the cortex and basal ganglia is discussed as a pathophysiological correlate of PD further focus was laid on autocorrelations and crosscorrelations of simultaneously recorded neurons to test this recent hypothesis. The results will be presented at the meeting.