Cortical histopathology following stimulation with metallic and carbon electrodes.

Stimulation of the cat striate cortex with polished 1 mm2 gold, platinum, rhodium or carbon electrodes for 40h, at 50 Hz, and 0.5 msec duration, results in tissue damage at current densities of 0.6 A/cm2. At 0.1 A/cm2 rhodium and carbon were toxic to brain. In vitro gold and platinum corroded after 1,500-2,300 h of testing in simulated cerebrospinal fluid. The materials utilized are not suitable for long-term chronic electrodes for neural prosthetics.