Implantable neural electrodes have enjoyed decades of development but the ability to record resolvable neuronal activities is often reduced or completely lost over time. This is true regardless of species with recording lifetimes of months to at best a few years in animal; although select neural probes have been successfully implemented in human, the recording lifetimes are short (<5 years). Overcoming the limitations of today?s implant technologies could revolutionize the design of future neural prosthetic platforms, which in turn, would have a profound impact on the medical treatment of multiple neurological disorders using brain-machine interfaces. The goal of this proposal is to achieve large scale recordings over long periods of time. To achieve a stable, long-term neuronal interface, we will use a multi-pronged approach involving innovation in polymer micromachining and integration and packaging and the application of principles of solid mechanics and beam theory. Multi-level polymer micromachining will enable high electrode density on both sides of single shanks with minimal area dedicated to wiring. Multiple shanks will be connected by a backplane consisting of a ribbon cable into which electrical connectivity has been established with an embedded application specific integrated circuit (ASIC) chip. The chip contains circuits that provide signal amplification and multiplexing; the latter will greatly reduce the number of external wire connections and thus the footprint required for the overall implant. By leveraging the increase in stiffness of a shank as length decreases and biodegradable polymers, deep implantation of bare probes and probe arrays will be realized without the use of existing stiffener approaches that increase the cross sectional diameter by orders of magnitude. The collaborative team consists of biomedical engineer with specific expertise in microfabrication of implantable systems, a circuit expert, and a biomedical engineer with expertise in neural engineering of hippocampal prostheses. Together, we will develop the probe array technology and achieve integration of microelectronic circuits. In addition, the new probe array system will be demonstrated in rat to collect electrophysiological recordings in the hippocampus and compared to the performance of gold standard microwire array implants. These studies will be complemented by histological analysis.