Abstract
In recent years, optogenetics has become a central tool in neuroscience research. Estimating the transmission of visible light through brain tissue is of crucial importance for controlling the activation levels of neurons in different depths, designing optical systems, and avoiding lesions from excessive power density. The Kubelka–Munk model and Monte Carlo simulations have previously been used to model light propagation through rodents' brain tissue, however, these prior attempts suffer from fundamental shortcomings. Here, we introduce and study two modified approaches for modeling the distributions of light emanating from a multimode fiber and scattering through tissue, using both realistic numerical Monte Carlo simulations and an analytical approach based on the beam-spread function approach. We demonstrate a good agreement of the new methods' predictions both with recently published data, and with new measurements in mouse brain cortical slices, where our results yield a new cortical scattering length estimate of ∼47 µm at λ = 473 nm, significantly shorter than ordinarily assumed in optogenetic applications.
Highlights
Optogenetic neuromodulation is playing an increasingly central role in neuroscience research and emerging ap-Received May 31, 2015; accepted October 30, 2015; First published January 4, 2016. 1The authors report no conflict of interest. 2Contributions: G.Y., I.K., and S.S. designed research; G.Y. and N.M.performed research; G.Y. and S.S. analyzed data and wrote the paper.plications (Deisseroth, 2011), with major efforts being directed toward the discovery and development of advanced optogenetic probes (Yizhar et al, 2011; Zhang et al, 2011) and related miniature devices (Deisseroth and Schnitzer, 2013)
We first examined the accuracy of beam spread function (BSF) method by comparing it to MC simulation results using two sets of previously published brain tissue optical parameters: scattering coefficient s ϭ168.6 cmϪ1 from Al-Juboori et al (2013) measured in the mouse’s pedunculopontine nucleus using 453 nm blue light and s ϭ120 cmϪ1 from Yaroslavsky et al (2002) measured in human brain graymatter tissue using 480 nm blue light
Due to the lack of better data, we used the absorption coefficient and anisotropy factor of native human gray matter from Yaroslavsky et al (2002): a ϭ 0.6 cmϪ1 and g ϭ 0.88 in both cases. These results illustrate that the analytical BSF method generally follows the MC predictions quite closely for a parameter regime, which is relevant for optogenetics
Summary
Optogenetic neuromodulation is playing an increasingly central role in neuroscience research and emerging ap-Received May 31, 2015; accepted October 30, 2015; First published January 4, 2016. 1The authors report no conflict of interest. 2Contributions: G.Y., I.K., and S.S. designed research; G.Y. and N.M.performed research; G.Y. and S.S. analyzed data and wrote the paper.plications (Deisseroth, 2011), with major efforts being directed toward the discovery and development of advanced optogenetic probes (Yizhar et al, 2011; Zhang et al, 2011) and related miniature devices (Deisseroth and Schnitzer, 2013). Optogenetic neuromodulation is playing an increasingly central role in neuroscience research and emerging ap-. Received May 31, 2015; accepted October 30, 2015; First published January 4, 2016. Plications (Deisseroth, 2011), with major efforts being directed toward the discovery and development of advanced optogenetic probes (Yizhar et al, 2011; Zhang et al, 2011) and related miniature devices (Deisseroth and Schnitzer, 2013).
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