title: Multiplexed neural recording along a single optical fiber via optical reflectometry.
abstract: We introduce the design and theoretical analysis of a fiber-optic architecture for neural recording without contrast agents, which transduces neural electrical signals into a multiplexed optical readout. Our sensor design is inspired by electro-optic modulators, which modulate the refractive index of a waveguide by applying a voltage across an electro-optic core material. We estimate that this design would allow recording of the activities of individual neurons located at points along a 10-cm length of optical fiber with 40-μm axial resolution and sensitivity down to 100  μV using commercially available optical reflectometers as readout devices. Neural recording sites detect a potential difference against a reference and apply this potential to a capacitor. The waveguide serves as one of the plates of the capacitor, so charge accumulation across the capacitor results in an optical effect. A key concept of the design is that the sensitivity can be improved by increasing the capacitance. To maximize the capacitance, we utilize a microscopic layer of material with high relative permittivity. If suitable materials can be found—possessing high capacitance per unit area as well as favorable properties with respect to toxicity, optical attenuation, ohmic junctions, and surface capacitance—then such sensing fibers could, in principle, be scaled down to few-micron cross-sections for minimally invasive neural interfacing. We study these material requirements and propose potential material choices. Custom-designed multimaterial optical fibers, probed using a reflectometric readout, may, therefore, provide a powerful platform for neural sensing.
authors.affiliation: MIT Media Lab, E15-421, 20 Ames Street, Cambridge, Massachusetts 02139, United StatesbMassachusetts Institute of Technology, Department of Physics, 4-315, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Samuel G
authors.initials: SG
authors.lastname: Rodriques
authors.affiliation: MIT Media Lab, E15-421, 20 Ames Street, Cambridge, Massachusetts 02139, United States.
authors.forename: Adam H
authors.initials: AH
authors.lastname: Marblestone
authors.affiliation: MIT Media Lab, E15-421, 20 Ames Street, Cambridge, Massachusetts 02139, United States.
authors.forename: Jorg
authors.initials: J
authors.lastname: Scholvin
authors.affiliation: MIT Media Lab, E15-421, 20 Ames Street, Cambridge, Massachusetts 02139, United States.
authors.forename: Joel
authors.initials: J
authors.lastname: Dapello
authors.affiliation: MIT Media Lab, E15-421, 20 Ames Street, Cambridge, Massachusetts 02139, United States.
authors.forename: Deblina
authors.initials: D
authors.lastname: Sarkar
authors.affiliation: Harvard University, Department of Chemistry and Chemical Biology, 12 Oxford Street Cambridge, Massachusetts 02138, United States.
authors.forename: Max
authors.initials: M
authors.lastname: Mankin
authors.affiliation: MIT Media Lab, E15-421, 20 Ames Street, Cambridge, Massachusetts 02139, United States.
authors.forename: Ruixuan
authors.initials: R
authors.lastname: Gao
authors.affiliation: Bellevue, Washington, United States.
authors.forename: Lowell
authors.initials: L
authors.lastname: Wood
authors.affiliation: MIT Media Lab and McGovern Institute, Departments of Brain and Cognitive Science and Biological Engineering, United States.
authors.forename: Edward S
authors.initials: ES
authors.lastname: Boyden
mesh_terms: D004867:Equipment Design; D006801:Humans; D009474:Neurons / Q000502:physiology*; D009482:Neurophysiology / Q000295:instrumentation* / Q000379:methods*; D055100:Optical Fibers; D055095:Optics and Photonics / Q000295:instrumentation; D012031:Refractometry