Mr. Hector D. Tejeda Profile

Hector D. Tejeda

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Proceedings Article | 8 March 2013 Paper

Comparison between Bessel and Gaussian beam propagation for in-depth optogenetic stimulation

Hector Tejeda, Ting Li, Samarendra Mohanty

Proceedings Volume 8586, 85860G (2013) https://doi.org/10.1117/12.2005555

KEYWORDS: Bessel beams, Gaussian beams, Optogenetics, Beam propagation method, Brain, Axicons, Monte Carlo methods, Fiber optics, Optical simulations, Wave propagation

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Optogenetics technology has opened new landscapes for neuroscience research. Due to its non-diffracting and selfhealing nature, Bessel beam has potential to improve in-depth optogenetic stimulation. A detailed understanding of Bessel beam propagation, as well as its superiority over commonly used Gaussian beam, is essential for delivery and control of light irradiation for optogenetics and other light stimulation approaches. We developed an algorithm for modeling Bessel beam propagation and then compared both beam propagations in two-layered mice brain under variance of multiple variables (i.e., wavelength, numerical aperture, and beam size). These simulations show that Bessel beam is significantly advantageous over Gaussian beam for in-depth optogenetic stimulation, leading to development of lessinvasive probes. While experimental measurements using single-photon Bessel-Gauss beam generated by axicon-tip fiber did not show improved stimulation-depth, near-infrared Bessel beam generated using free-space optics and an axicon led to better penetration than near-infrared Gaussian beam.

Proceedings Article | 22 February 2012 Paper

Fiber-array based optogenetic prosthetic system for stimulation therapy

Ling Gu, Chris Cote, Hector Tejeda, Samarendra Mohanty

Proceedings Volume 8207, 82076E (2012) https://doi.org/10.1117/12.910036

KEYWORDS: Optical fibers, Light emitting diodes, Brain, Optogenetics, Visual cortex, Retina, Electrodes, Neurons, Nervous system, Tissues

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Recent advent of optogenetics has enabled activation of genetically-targeted neuronal cells using low intensity blue light with high temporal precision. Since blue light is attenuated rapidly due to scattering and absorption in neural tissue, optogenetic treatment of neurological disorders may require stimulation of specific cell types in multiple regions of the brain. Further, restoration of certain neural functions (vision, and auditory etc) requires accurate spatio-temporal stimulation patterns rather than just precise temporal stimulation. In order to activate multiple regions of the central nervous system in 3D, here, we report development of an optogenetic prosthetic comprising of array of fibers coupled to independently-controllable LEDs. This design avoids direct contact of LEDs with the brain tissue and thus does not require electrical and heat isolation, which can non-specifically stimulate and damage the local brain regions. The intensity, frequency, and duty cycle of light pulses from each fiber in the array was controlled independently using an inhouse developed LabView based program interfaced with a microcontroller driving the individual LEDs. While the temporal profile of the light pulses was controlled by varying the current driving the LED, the beam profile emanating from each fiber tip could be sculpted by microfabrication of the fiber tip. The fiber array was used to stimulate neurons, expressing channelrhodopsin-2, in different locations within the brain or retina. Control of neural activity in the mice cortex, using the fiber-array based prosthetic, is evaluated from recordings made with multi-electrode array (MEA). We also report construction of a μLED array based prosthetic for spatio-temporal stimulation of cortex.

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