11. Microelectrode recordings in the framework of neuromodulation

Introduction Microelectrode recordings (MER) in humans offer a fascinating modality to study neuropathophysiology and neurosciences. While MER is conducted during surgeries for deep brain stimulation (DBS) in patients with movement disorders, our principal goal was here to exploit MER to optimize and better understand effects of cerebral electrical stimulation. In this framework, we established a platform to record and analyse MER in humans, not only in patients with movement disorders but also in patients with epilepsy. We present here the evaluation of different electrodes and first analyses of MER, recorded simultaneously or not to DBS. Methods Different types of microelectrodes (μE) have been evaluated for cortical or depth recordings in 8 patients. Fast ripples were automatically detected by online algorithm. Neuronal spikes are extracted from multi-unit recordings with homemade software, for clustering and auto-correlation. Multi-unit activities were recorded simultaneously to 1 Hz stimulation in patients with epilepsy (biphasic pulses, 450 μs or 60 μs/ph, 500 μA for macrostimulation; 25 μA and 60 μs/ph for microstimulation, 3 minute). Results Eight patients with epilepsy participated in the study (3 subdural, 7 depth electrodes). The MER of the 3 patients with cortical μE and two patients with μE on depth electrodes (Ad-Tech®) did not show any spikes, probably because of unsuitable length of contacts. In 5/7 patients with μE at the distal end of depth electrodes, spikes could be recorded for 4–10 days. Different pattern recorded from the hippocampus or from cortical dysplasia were compared to those recorded in the subthalamic nucleus or to the substantia nigra. High frequency oscillations (up to 700 Hz) were detected at the epileptic focus in 2 patients. Preliminary MER recorded during 1 Hz macrostimulation did not show increase of firing in all 5 patients who participated to DBS, while microstimulation (1 Hz), conducted in one patient with cortical dysplasia, induced significant increase in spike firings ( p Conclusions A platform to record μE is now established, offering MER in patients with epilepsy, in addition to patients with movement disorders undergoing DBS surgery. For the first time in humans, we showed that the microstimulation showed an excitatory effect at 1 Hz stimulation. Microstimulation appears here as valuable complementary tool to better understand the effects of DBS.