Abstracts

Rationale: The success of neural prostheses strongly depends on the long-term viability of the electrode-tissue interface. No currently available neural recording electrode permits the long-term, high fidelity recording of neuronal activity. Among other factors, this is largely a result of the interrelated rigidity and size required to accurately position deep brain electrodes. These factors lead to trauma from device insertion and long-term damage at the electrode-tissue interface, as the rigid electrode, fixed to the cranium, aggravates the foreign-body response at the electrode-tissue interface. This damage is believed to cause glial encapsulation and loss of signal fidelity over time. Flexible, sub-25 m electrodes lessen trauma from insertion and reduce the materials mismatch between the electrode and tissue. However, electrode flexibility presents a challenge in accurate deep-brain insertion.Methods: We describe a magnetic insertion system consisting of a high capacity rapid discharge unit, a driver coil and a glass pipette ejection tube. Microelectrodes are made using ferritic 430 stainless steel vapor coated in Parylene at a diameter of 25 m. A current pulse from the discharge unit through the coil generates a transient magnetic field around the ejection tube containing the microelectrode, propelling it into deep brain structures with great precision and accuracy. The magnetic microelectrode is stereotactically deployed through a small via in a liquid crystal polymer (LCP) substrate that is pre-mounted over the craniotomy on the skull surface. The LCP substrate houses the recording circuitry necessary to interface with the magnetic microelectrode. Results: We demonstrate successful implantation within the epileptic focus of a kainic acid rat model of temporal lobe epilepsy. The magnetic insertion system design is characterized and presented with an implantable platform allowing chronic recording of single-unit activity from behaving animals. Probes are electrically characterized prior to insertion and over time to correlate histologically observed changes with electrically measured changes at the electrode-tissue interface.Conclusions: We present data on the chronic performance of flexible microelectrodes implanted with the magnetic insertion system. Along with the LCP recording platform, this technology makes chronic monitoring of small neuronal populations possible in behaving rat and mouse models of temporal lobe epilepsy (TLE). Additionally, sub-25 m electrodes may enable improved closed-loop cortical prostheses in humans.