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1.
Figure 3

Figure 3. Strategies for targeting light to 3-dimensionally distributed structures in the brain. From: Optogenetic tools for analyzing the neural circuits of behavior.

(a) Example strategy for efficienctly docking an array of optical fibers or waveguides (Figure 2 (a)) to an array of lightsources (Figure 2 (b) (i)), for independent control of neural activity in a large number (e.g., a dozen or more) structures distributed throughout the brain. An aligner plate that holds the optical fibers, can easily be docked to the array of LEDs. Shown is an example of a 14-fiber array for bilateral targeting of 14 independently-accessible points within the mouse hippocampus. (b) Photograph of a device made according to the schematic shown in (a).

Jacob G. Bernstein, et al. Trends Cogn Sci. ;15(12):592-600.
2.
Figure 2

Figure 2. Methods for delivering light to the brain of behaving mammals, and miniature light sources for generation of light. From: Optogenetic tools for analyzing the neural circuits of behavior.

(a) (i) Mouse with implanted cannula, into which is inserted an optical fiber (200 microns in diameter), for light delivery to deep brain regions. (ii) Chronically implantable optical fiber (200 microns in diameter), mounted inside a ferrule. The fiber is inserted into the brain, with the ferrule projecting outwards for later connection to a corresponding ferrule-mounted fiber coupled to a laser. (iii) Microfabricated multi-waveguide arrays, for delivery of light to multiple points along the insertion axis of the probe. The probe shown here is similar in thickness to a typical optical fiber inserted into the brain, but can deliver light to a dozen different sites along the axis of the probe. Adapted from [77]. (b) (i) Schematic depicting a headborne device comprising an array of LEDs (500–1000 microns in dimension, e.g. raw die LEDs from Cree or other vendors) mounted on a LED holder (which serves as heat sink as well as an electrical connection), for illumination of multiple (e.g., a dozen or more) structures on the surface of the brain. Such a device weighs a gram or less and can contain many independently-controlled illuminators; the electrical connector conveys currents from LED driver chips. Adapted from [78]. (ii) Circuitry that mounts on top of the LED array shown in (b) (i), enabling fully wireless power delivery, and wireless control of the LEDs. The power module receives broadcast energy, and the motherboard module enables control of the LEDs below; the radio module enables programs to be uploaded to the module. Adapted from [78]. (iii) A mouse with implanted optics module ((b) (i)) and bearing the wireless power module ((b) (ii)). Adapted from [78].

Jacob G. Bernstein, et al. Trends Cogn Sci. ;15(12):592-600.
3.
Figure 1

Figure 1. Molecular tools enabling activation and silencing of neurons with light. From: Optogenetic tools for analyzing the neural circuits of behavior.

(a) (i) Diagram showing the physiological effect of expressing the gene for the light-driven inward cation channel channelrhodopsin-2 (ChR2) from the green alga C. reinhardtii in a neuron and illuminating the cell. Positively charged ions (chiefly sodium and protons, but also to a lesser extent potassium and calcium) flow into the intracellular space, from the extracellular space. (ii) Raw voltage trace (black trace) recorded, using whole-cell current clamp, from a cultured hippocampal neuron expressing ChR2 and illuminated with brief pulses of blue light (blue dashes under trace) from a mercury arc lamp through a GFP excitation filter, showing light-driven action potentials. Adapted from [13]. (b) (i) Diagram showing the physiological effect of expressing the gene for the light-driven inward chloride pump halorhodopsin (Halo/NpHR) from the archaeal species N. pharaonis in a neuron and illuminating the cell. Negatively charged chloride ions flow into the cell. (ii) Raw voltage trace (black trace) recorded, using whole-cell current clamp, from a cultured hippocampal neuron expressing Halo and illuminated with orange light (orange dashes under trace) from a xenon lamp through a Texas Red excitation filter, showing light-driven action potential silencing. Action potentials were elicited by injecting brief pulses of current into the cell body (~300 pA, 4 ms-duration pulses) at a rate of 5 Hz. Adapted from [28]. (c) (i) Diagram showing the physiological effect of expressing the gene for the light-driven outward proton pump archaerhodopsin-3 (Arch) from the archaeal species H. sodomense a neuron and illuminating the cell. Positively charged protons flow out of the cell. (ii) Neural activity in a representative neuron recorded using extracellular electrode recording in an awake mouse before, during, and after 5 seconds of yellow light illumination, shown as a spike raster plot (top), and as a histogram of instantaneous firing rate averaged across trials (bottom, bin size, 20 ms).

Jacob G. Bernstein, et al. Trends Cogn Sci. ;15(12):592-600.

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