A hybrid clinical-research depth electrode for acute and chronic in vivo microelectrode recording of human brain neurons. Technical note.

For several decades, important scientific information has been gained from in vivo microelectrode recordings of individual human cerebral cortical neurons in patients with epilepsy. The experimental methods used, however, are technically complex and require a highly skilled intraoperative team. There are also significant experimental time limitations, as well as constraints on the type of behavioral tests conducted, and the brain regions that may be safely studied. In this report, a new method is described for obtaining in vivo microelectrode recordings using a hybrid depth electrode (HDE). High-impedance research recording contacts are interspersed between low-impedance clinical electroencephalographic (EEG) contacts along the HDE shaft. The HDE has the same external physical properties as a standard clinical depth electrode (DE). Following preclinical laboratory testing, 15 HDEs were used in the evaluation of six patients with medically refractory epilepsy. High-quality EEG recordings were obtained in all cases (two acute intraoperative, four from the chronic epilepsy monitoring unit). Action potentials from individual neurons were successfully recorded during all experimental sessions; however, the chronic preparations were clearly superior. Chronic HDEs are placed using a standard stereotactic system, and the locations of recording contacts are documented on a postimplantation imaging study. The quality of the chronic research recordings was excellent over study periods ranging from 5 to 14 days. The patients rested comfortably on the ward and were able to cooperate with complex experimental instructions. Basic neuroscientists participated fully in all aspects of the chronic investigations. The use of an HDE in place of a standard clinical DE may now allow detailed physiological investigations of any brain region targeted for clinical DE implantation.