Sight can be restored in patients who lost photoreceptors due to atrophic AMD by substituting them with a photovoltaic array. Subretinal pixels convert pulsed NIR light projected from augmented-reality glasses into electric current, stimulating the nearby inner retinal neurons. Patients with such implants can simultaneously use their residual peripheral sight and central prosthetic vision, and its acuity closely matches the 100um pixel size of the implant. We present two approaches to selective neural stimulation with pixel sizes down to 20um – optically configurable current steering and 3-dimensional honeycomb-shaped electrodes, both providing prosthetic acuity matching the natural resolution in rats.
Nanometer-scale deformations of the neuron accompany the action potential. These displacements are measured using a fast quantitative phase microscope and averaged in synchrony with optogenetic stimulation of cultured neurons. The phase movie is further processed by leveraging the spatial and temporal distribution of the spiking signal to detect and segment the separate action potentials in individual cells. An accompanying confocal fluorescence microscopy provides the 3-D cell shape for calibration of the refractive index to calculate the mechanical displacements from the optical phase. Together, these results illuminate the underlying mechanism of the cellular deformations and techniques for achieving all-optical single spike detection.
We report the full-field imaging of the mechanical deformations accompanying the action potential in primary cortical neurons using ultrafast quantitative phase imaging (QPI) with a temporal resolution of 0.1 ms and a membrane displacement sensitivity of <0.2 nm per pixel. The average displacements were ~0.7 nm on cell somas and ~0.5 nm on neurites. Finite element modeling based on the 3D shape extracted from confocal imaging and on scaling of the surface tension with trans-membrane voltage yielded the deformation map during action potential, which matched the features of the experimental results, including the displacement amplitude, time course, and spatial distribution.
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