A fine-scale and minimally invasive marking method for use with conventional tungsten microelectrodes.

In neurophysiology, achieving precise correlation between physiological responses and anatomical structures is a significant challenge. Therefore, the accuracy of the electrode marking method is crucial. In this study, we describe a tungsten-deposition method, in which tungsten oxide is generated by applying biphasic current pulses to conventional tungsten electrodes. The electrical current used was 40-50 µA, which is similar to that used in electrical microstimulation experiments. The size of the markings ranged from 10 µm to 100 µm, corresponding to the size of the electrode tip, which is smaller than that of existing marking methods. Despite the small size of the markings, detection is easy as the marking appears in bright red under dark-field observation after Nissl staining. This marking technique resulted in low tissue damage and was maintained in vivo for at least 2 years. The feasibility of this method was tested in mouse and macaque brains. Significance Statement A new marking method was developed to identify the recording site for conventional tungsten microelectrodes. Applying biphasic pulse current oxidizes the tip of the tungsten electrode, then the oxides are deposited around the recording site to form a marking. The markings were smaller than those formed in existing methods, caused less damage to the brain tissue, remained for at least 2 years, and were easy to identify by dark-field observation after cresyl violet staining.