Extracellular stimulation of mouse retinal ganglion cells with non-rectangular voltage-controlled waveforms

Neural prostheses rely upon electric stimulation to control neural activity. However, electrode corrosion and tissue damage may result from the injection of high charge densities. During electrical stimulation with traditional voltage-controlled square-wave pulses, the current density distribution on the surface of the stimulating electrode is highly nonuniform, with the highest current densities located at the edge of disk-shaped electrodes. Current density is implicated in tissue damage and electrode corrosion because it determines the charge density distribution. Through recent computer modeling work, we have found that Gaussian and sinusoidal stimulus waveforms produce a current density distribution that is significantly more uniform than the one produced by square-wave pulses. In this manner, these non-rectangular waveforms reduce the peak current densities without decreasing the efficacy of the neural stimulus. In the present work, we utilize an in vitro mouse retinal preparation to compare the same set of alternative stimulus waveforms. The -1V amplitude voltage-controlled stimuli were delivered through 20 mum diameter titanium nitride electrodes. Importantly, when normalized for the amount of injected charge, the data demonstrate that each waveform is similarly effective at eliciting a neural response. Also, the suprathreshold Gaussian and sinusoidal waveforms possessed much lower peaks in current. For this reason, these non-rectangular waveforms may be useful in reducing electrode corrosion and tissue damage.