Non-rectangular waveforms for neural stimulation with practical electrodes

Abstract

Historically the rectangular pulse waveform has been the choice for neural stimulation. The strength-duration curve is thus defined for rectangular pulses. Not much attention has been paid to alternative waveforms to determine if the pulse shape has an effect on the strength-duration relation. Similarly the charge injection capacity of neural electrodes has also been measured with rectangular pulses. In this study we questioned if non-rectangular waveforms can generate a stronger stimulation effect, when applied through practical electrodes, by minimizing the neural activation threshold and maximizing the charge injection capacity of the electrode. First, the activation threshold parameters were studied with seven different pulse shapes using computer simulations of a local membrane model. These waveforms were rectangular, linear increase and decrease, exponential increase and decrease, Gaussian, and sinusoidal. The chronaxie time was found to be longer with all the non-rectangular pulses and some provided more energy efficient stimulation than the rectangular waveform. Second, the charge injection capacity of titanium nitride microelectrodes was measured experimentally for the same waveforms. Linearly decreasing ramp provided the best charge injection for all pulse widths tested from 0.02 to 0.5 ms. Finally, the most efficient waveform that maximized the charge injection capacity of the electrode while providing the lowest threshold charge for neural activation was searched. Linear and exponential decrease, and Gaussian waveforms were found to be the most efficient pulse shapes.

Response of the Hodgkin-Huxley Neuron to a Periodic Sequence of Biphasic Pulses

“…During this relatively short time one may be able to avoid Faradaic reactions that would occur at higher levels of total charge with longer pulses. Similar conclusion was reached in a study of Sahin and Tie [11] who investigated eects of non-rectangular wave forms on threshold both experimentally and theoretically within a simple local model of a mammalian nerve [58,59]. Their model is similar to the HH model except for the absence of the potassium channel.…”

“…Selection of the most ecient waveform shape and duration, such that delivered charge, energy and power are simultaneously optimized is a dicult task [15,16]. Most studies indicate that non-rectangular pulses are more energy efcient than rectangular ones [11,13,14,16].…”

Optimal stimulus profiles for neuroprosthetic devices: Monophasic versus biphasic stimulation

“…Among the methods that can improve the performance of neuroprosthetic devices, the design of optimal stimuli has attracted considerable attention recently [9], [10], [11], [12], [13], [14], [15], [16], [17].…”

Evaluating the use of different waveforms for intravesical electrical stimulation: A study in the rat

“…Several studies showed interesting data in other applications on the influence of the waveform on the efficacy and the response of nerve stimulation. [16][17][18][19]21 Besides, more and more studies have revealed that some waveforms, like biphasic waveforms, are preferred by the patients 14,15 for ES.…”