Reply to "Energy Optimal Stimulation Waveforms, Or Not: Comments on 'An Investigation of Neural Stimulation...

We thank Professors Grill and Wongsarnpigoon for their detailed responses prompted by our recent publication [1] in this journal. We welcome the opportunity we have had for discussion and thank the Editor for his invitation to make this further contribution. We made our experiments partly in the light of the statements in the abstract of their relevant paper [2] that energy optimal genetic algorithm (GA) waveforms "resembled truncated Gaussian curves" and that "if used in implantable neural stimulators, GA-optimized waveforms could prolong battery life, thereby reducing the frequency of recharge intervals, the volume of implanted pulse generators, and the costs and risks of battery-replacement surgeries." The authors discussed the practical consequences of both a 5% increase and a 60% increase in energy efficiency in the final statement of the paper and acknowledged that to include the cost of generating the GA waveforms might change the predicted optimal shape. Although mentioned only once, a claim of up to 60% relative energy savings is of great interest to those who design and use neural stimulators. Based on our in-vivo investigation of neural stimulation efficiency with biphasic Gaussian waveforms, we reported an upper potential of 17% energy savings over rectangular biphasic pulses. Furthermore, we added the consideration of instantaneous power requirement in our paper to further inform this discussion. This is a crucial parameter, especially to set the practical performance of the sharp-peaked GA waveforms into perspective, given that they deliver the majority of the cathodic charge in a time much shorter than the nominal phase duration.