Abstract
Optogenetics promises spatiotemporal precise control of neural processes using light. However, the spatial extent of illumination within the brain is difficult to control and cannot be adjusted using standard fiber optics. We demonstrate that optical fibers with tapered tips can be used to illuminate either spatially restricted or large brain volumes. Remotely adjusting the light input angle to the fiber varies the light-emitting portion of the taper over several millimeters without movement of the implant. We use this mode to activate dorsal versus ventral striatum of individual mice and reveal different effects of each manipulation on motor behavior. Conversely, injecting light over the full numerical aperture of the fiber results in light emission from the entire taper surface, achieving broader and more efficient optogenetic activation of neurons when compared to the standard flat-faced fiber stimulation. Thus, tapered fibers permit focal or broad illumination that can be precisely and dynamically matched to experimental needs.
Highlights
Optogenetic modulation of neuronal activity has become the dominant method of examining the behavioral consequences of activity in specific neuronal populations in vivo
A ray injected into the core of the fiber with an input angle θ is guided via total internal reflection (TIR) to the tapered region
At each reflection of the ray its propagation angle with respect to the fiber optical axis increases by an amount equal to the taper angle ψ (Fig. S1). This occurs until a critical section is met, at which TIR is lost and the ray radiates into the surrounding medium
Summary
Optogenetic modulation of neuronal activity has become the dominant method of examining the behavioral consequences of activity in specific neuronal populations in vivo. It is necessary to deliver uniform illumination to large brain areas, whereas for others confined illumination of small brain volumes is preferred Both modes of illumination could be accomplished via a single, reconfigurable device. To this aim several approaches have been developed, including multiple implanted waveguides[8,9,10], multiple micro light delivery devices (μLEDs)[6,7,11,12], holographic illumination via headmounted objectives[13] and multi-point emitting optical fibers (MPFs)[14,15]. Due to the relatively large and flat area of the cleaved end, these fibers can cause substantial tissue damage during insertion
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