Challenging the optimality of rectangular pulse stimulation for neuroprosthetic devices

Rectangular Lilly-type pulse stimuli have been used extensively in the context of electrical stimulation of neurons. However, the optimality of rectangular pulses has not been proven rigorously. In this paper, we challenge the optimality of rectangular pulse stimuli from a control engineering perspective through introducing and solving an optimisation problem. We introduce two stimulation efficiency measures to compare the charge and energy efficiency of optimal and rectangular pulse stimuli, and show that these measures increase for long duration stimuli. Therefore, non-rectangular optimal pulse waveforms result in more efficient stimulation of neurons, which can be used in the design of improved stimulus strategies for neuroprosthetic devices.