Targeted Neuromodulation by Nanosecond Pulsed Electric Fields

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Nanosecond pulsed electric field (nsPEF) is a new modality for neuromodulation, with unique capabilities qualitatively different from the conventional electrostimulation. The potential benefits of nsPEF include but are not limited to prolonged stimulation with little or no electrochemical side effects; excitation at lower thresholds; selectivity based on cell charging time constant; the capability of choosing between stimulation, inhibition, and ablation; and achieving these effects non-invasively, either for outpatient deep brain stimulation or for tumor ablation. The primary effect of nsPEF is a rapid build-up of cell membrane potential (MP). Real-time measurements of MP kinetics are a key to predicting the outcomes of nsPEF stimulation. They are also a key to understanding bipolar cancellation, a unique feature that enables interference targeting of nsPEF for non-invasive neuromodulation. However, membrane charging by nsPEF occurs on a nanosecond time scale, much faster than could be resolved by the existing electrophysiological and imaging methods. We have addressed this challenge by implementing strobe pulsed laser microscopy for MP imaging with better than 50 ns accuracy. In this one-of-a-kind set-up, cells loaded with a fast voltage-sensitive fluorescence dye are exposed to high-power momentary laser flashes (5 kW, 6 ns). The flashes are dynamically synchronized with nsPEF stimulation of target cells. Photos of fluorescence taken at different times during and after nsPEF show the real-time dynamics of MP changes and how these changes culminate in downstream effects, such as opening of voltage gated ion channels, initiation of action potentials, and nanoelectroporation. We will employ this all-new set-up for understanding fine mechanisms and principles how neurons respond to the nanosecond electric stress. We will characterize nsPEF parameters needed to evoke the desired neuromodulation effect and tune the interference targeting protocols to achieve this effect at a distance from stimulating electrodes. We will perform finite element modeling of the electric field thresholds and use our in vitro results to define the feasibility and nsPEF requirements for non-invasive deep brain stimulation. This project will generate new basic knowledge of neuronal function, including nanosecond-scale biophysics of the cell membrane and ion channels. We will systematically characterize nsPEF neuromodulation effects and link them to dielectric and physiological properties of neurons and to nsPEF stimulation parameters. This in vitro project will utilize R21 “high risk, high reward” concept to collect mechanistic and quantitative data necessary for animal and human studies of nsPEF neuromodulation.