title: Scattering of Sculpted Light in Intact Brain Tissue, with implications for Optogenetics.
abstract: Optogenetics uses light to control and observe the activity of neurons, often using a focused laser beam. As brain tissue is a scattering medium, beams are distorted and spread with propagation through neural tissue, and the beam's degradation has important implications in optogenetic experiments. To address this, we present an analysis of scattering and loss of intensity of focused laser beams at different depths within the brains of zebrafish larvae. Our experimental set-up uses a 488 nm laser and a spatial light modulator to focus a diffraction-limited spot of light within the brain. We use a combination of experimental measurements of back-scattered light in live larvae and computational modelling of the scattering to determine the spatial distribution of light. Modelling is performed using the Monte Carlo method, supported by generalised Lorenz-Mie theory in the single-scattering approximation. Scattering in areas rich in cell bodies is compared to that of regions of neuropil to identify the distinct and dramatic contributions that cell nuclei make to scattering. We demonstrate the feasibility of illuminating individual neurons, even in nucleus-rich areas, at depths beyond 100 μm using a spatial light modulator in combination with a standard laser and microscope optics.
authors.affiliation: School of Mathematics and Physics, The University of Queensland, Brisbane QLD, Australia.
authors.forename: Itia A
authors.initials: IA
authors.lastname: Favre-Bulle
authors.affiliation: School of Mathematics and Physics, The University of Queensland, Brisbane QLD, Australia.
authors.forename: Daryl
authors.initials: D
authors.lastname: Preece
authors.affiliation: School of Mathematics and Physics, The University of Queensland, Brisbane QLD, Australia.
authors.forename: Timo A
authors.initials: TA
authors.lastname: Nieminen
authors.affiliation: School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia.
authors.forename: Lucy A
authors.initials: LA
authors.lastname: Heap
authors.affiliation: 1] School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia [2] Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia.
authors.forename: Ethan K
authors.initials: EK
authors.lastname: Scott
authors.affiliation: School of Mathematics and Physics, The University of Queensland, Brisbane QLD, Australia.
authors.forename: Halina
authors.initials: H
authors.lastname: Rubinsztein-Dunlop
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology* / Q000528:radiation effects; D002467:Cell Nucleus / Q000737:chemistry / Q000528:radiation effects; D007814:Larva / Q000502:physiology; D008027:Light; D009010:Monte Carlo Method; D062308:Optogenetics; D012542:Scattering, Radiation; D015027:Zebrafish / Q000254:growth & development / Q000502:physiology