Mechanisms determining safety and performance of brain stimulating electrodes.

Electrical current is widely used to interact with or stimulate neural systems. Current transduction from device to tissue is mediated at the electrode-tissue interface by capacitive charge and electrochemistry. This charge-passing-capacity is frequency dependent. While safety parameters have been established for high-frequencies, safety has not been fully determined for novel materials and pulse frequencies significantly lower than 100 Hz. We are explicitly interested in safety parameters and performance of charge passing at low frequencies (<<100 Hz) for neural systems. We present a visual study of pH during charge passing for electrodeposited iridium oxide electrodes. Clear reaction-diffusion waves are observed that extend many hundreds of micrometers from the electrode surface.