The Perceptual Salience of Amplitude Modulated Cortical Stimulation: Peak Equivalence or RMS Equivalence?

Regele, Oliver B. M.S.B.M.E., Purdue University, May 2013. The Perceptual Salience of Amplitude Modulated Cortical Stimulation: Peak Equivalence or RMS Equivalence? Major Professor: Kevin Otto. Intracortical microstimulation (ICMS) is a method of electrically stimulating the primary motor, visual, somatosensory and auditory cortices in the brain. The goal is to replace deficient sensory function in cases such as deafness, blindness and paralysis. However these neural prosthetics have not made the full transition to clinical trials due to a lack of sufficient investigation into the optimal stimulation waveforms. Sinusoidally amplitude modulated (SAM) signals have been shown to be important to sensory systems, yet have not been fully explored as a stimulation waveform for stimulating cortical tissue. This work represents an investigation into the detection characteristics of electrical SAM in the auditory cortex. The specific aims of this work were: 1) Determine whether RMS or Peak content determines detectability of acoustic and electrical SAM signals. 2) Evaluate the effect on detection of varying the modulation frequency. 3) Determine whether detection of electrical SAM is driven by pulses per second, modulation frequency or an interaction between the two. 4) Determine the contribution of subthreshold pulses present in SAM signals to detection. Results indicated that for electrical signals, the peak content and the pulses per second were the main determinants of detectability, while modulation frequency was not significant. Further experiments found that square wave modulation, representing only the highest current amplitudes, could effectively replace SAM electrical stimulation in terms of detectability