Thumbtack microelectrode and method of making same field of the invention

A thumbtack microelectrode for making extracellular chronic recordings from single nerve cells in the cere bral cortex in unrestrained animals over prolonged pe riods of time comprises a rigid electrode shaft, which is microwelded to one side of a tack head-like disc, and a flexible electrical conductor which is mi crowelded to the opposite side of the tack head-like disc. After a cleaning operation including ultrasonic desiccation the entire microwelded assembly is electri cally insulated. The insulation covering the recording tip of the electrode shaft which is tapered, prior to the cleaning and insulating operations, by electrolytic etching, is then removed so as to expose a small area for use as the recording surface.