Phosphene Thresholds for V1 Stimulation Reflect the Strength-duration Curve of Neuronal Excitation Soroush Niketeghad; Abirami Muralidharan; Uday Patel; Jessy Dorn; Robert Greenberg; Nader Pouratian MD PhD Neurosurgical Mapping and Restoration Lab University of California Los Angeles

Introduction Method Results Conclusions •Stimulation of primary - •Subject: A blind volunteer with 8 Current abd charge thresholds for •The similar attributes of phosphene > subjective visual sensations called year history of bare perception. different pulse-width and frequency threshold curves and strength-duration “phosphenes”. •Primary goal: Assessing the values share the two basic curve of neuronal excitation -> •mechanism of phosphene perception feasibility of a visual cortical characteristics of the strength and Threshold mechanism of conscious -> neural correlates of conscious prosthesis. charge duration curve of neuronal visual perception may arise from V1 visual awareness. •Device: commercially available fully excitation: neuronal excitation threshold -> Direct •Transcrainal magnetic stimulation implanted neurostimulator (Neuropace 1) A rheobase current (the minimal involvement of V1 in visual awareness (TMS) & scalp EEG (Taylor, Walsh, RNS). amplitude of infinite pulse width) is •Our current knowledge of neuronal and Eimer 2010): •Electrodes: Two parallel cortical present in both curves. excitation can be employed to generate oMethod: Compared occipital EEG: strip leads (each with 4 contacts) 2) For the lowest amount of pulse- visual perception especially in the case phosphene-absent Vs. phosphene- implanted over the right medial width or frequency, a minimum of visual cortical prostheses. present trials for equal TMS charge is required to elicit a parameters. •Experiment: Measuring the phosphene and the extra charge oResult: Event_related potentials minimum current amplitude required increases linearly as pulse-width or Acknowledgement (ERPs) had similar morphology but to elicit a phosphene perception for frequency increase. This research was supported by higher amplitude for phosphene- different pulse-width and frequency SecondSight Inc. as a pilot study for present trials. values. assessing the safety and feasibility of oConclusion: There is a threshold visual cortical prosthetics. mechanism for generation of conscious phosphene perception. •Our hypotheis: threshold mechanism directly related to the threshold for References V1 neuronal excitation => share Merrill, Daniel R., Marom Bikson, and John G.R. the basic characteristric of neuronal Jefferys. 2005. “Electrical Stimulation of Excitable Tissue: Design of Efficacious and Safe excitation particularly the Protocols.” Journal of Neuroscience Methods. strength/charge duration curve https://doi.org/10.1016/j.jneumeth.2004.10.020 (Merrill, Bikson, and Jefferys 2005). . •We need to measure thresholds in Thresholds for different pulse-widths the form of current amplitude and Taylor, Paul C.J., Vincent Walsh, and Martin charge. Eimer. 2010. “The Neural Signature of Phosphene Perception.” Human Brain Mapping 31 •Electrical stimulation of the V1 via (9):1408–17. subdural electrodes. https://doi.org/10.1002/hbm.20941. Electrode placement & phosphene mapping

Thresholds for different frequencies

Strength-duration and charge duration Stimulation parameters curves