Optogenetic Stimulation of Human Neural Networks Using Fast Ferroelectric Spatial Light Modulator—Based Holographic Illumination

Abstract

Abstract:The generation and application of human stem-cell-derived functional neural circuits promises novel insights into neurodegenerative diseases. These networks are often studied using stem-cell derived random neural networks in vitro, with electrical stimulation and recording using multielectrode arrays. However, the impulse response function of networks is best obtained with spatiotemporally well-defined stimuli, which electrical stimulation does not provide. Optogenetics allows for the functional control of genetically altered cells with light stimuli at high spatiotemporal resolution. Current optogenetic investigations of neural networks are often conducted using full field illumination, potentially masking important functional information. This can be avoided using holographically shaped illumination. In this article, we present a digital holographic illumination setup with a spatial resolution of about 8 µm, which suffices for the stimulation of single neurons, and offers a temporal resolution of less than 0.6 ms. With this setup, we present preliminary single-cell stimulation recording of stem-cell derived induced human neurons in a random neural network. This will offer the opportunity for further studies on connectivity in such networks.

Tracking long-term functional connectivity maps in human stem-cell-derived neuronal networks by holographic-optogenetic stimulation

“…While full-field optogenetic stimulation resulted in robust neuronal network responses, precise sub-network activities were masked. We have combined holographic stimulation with MEA recordings (54), providing high spatial stimulation resolution of 8 µm spots. Prior to holographic stimulation, we took fluorescence images to visualize and manually map individual ChR2-EYFP-expressing neurons across the electrode grid.…”

“…Single-photon stimulation with computer-generated phase-modulating holograms is more flexible than the methods mentioned above: higher stimulation energies than DMD or organic light emitting diode (OLED) illumination are possible, as well as three-dimensional scanning (48), fiber-optic approaches are easier (51, 52), and even sample-induced aberrations can be compensated for (53). As the most flexible and economical path for our experiments, we chose to use single-photon stimulation with computer-generated holograms based on a ferroelectric SLM with switching times of up to 400 Hz, providing high spatial resolution stimuli at neuronal soma size (8 µm) with sufficient temporal resolution (2.5 ms) and high stimulation energies (0.15 W/mm 2 ) (54). Optogenetics has already been widely exploited for mapping microcircuits by targeting subsets of neurons in brain slices in vitro (55).…”

Optogenetics in Brain Research: From a Strategy to Investigate Physiological Function to a Therapeutic Tool

“…The in-vitro application of optogenetics in human-derived cells, provided the important evidence that this method could be applied to humans [134,135]. However, critical issues in optogenetic therapy remain the expression of optogenetic sensors in the human cell membrane and the current produced by individual actuators, properties that balance the possibility of improving a pathological condition with the risk of further neuronal damage [136].…”

Transmission Matrix Measurement of Multimode Optical Fibers by Mode-Selective Excitation Using One Spatial Light Modulator

“…This possibility has had a huge impact on several optical engineering techniques. It opened the door for coping with optical distortions in flow measurements, investigations of nonlinear phenomena in MMFs or neural networks by shaping the light in a proper way, which is called adaptive wavefront shaping (AWS) [15][16][17][18]. Within the presented work, AWS is used for an accurate mode excitation by shaping the MMF input wavefield with an SLM.…”