Connecting an optical fiber to an unrestrained freely moving animal raises the same issue as connecting wires: as the fiber twists it tends to exert an elastic force in the direction opposite to the twisting. This increases the chances of breaking the fiber and might impair the movements of the animal. The twisting effect can be minimized by using long (> 100 cm) and thin fibers. Alternatively, one can add a fiberoptic rotary joint (FoRJ) to allow free rotations of the fiber with minimum torque applied. Doric Lenses, Mightex Systems, Prizmatix and Thorlabs are manufacturing FoRJs suited to experiments on freely moving animals. These joints usually use high quality ball bearings for minimal friction during rotation. Some FoRJs such as Doric's ones integrate a pair of aspherical lenses for fiberoptic beam collimation and focusing. Doric Lenses also incorporate additionnal components into its FoRJs for intensity and/or wavelength division, electrical transmission and fluid delivery.
As a similar alternative, Plexon Inc. offers an electrical commutator, to which miniaturized LEDs can be mounted. These compact fiber-coupled LEDs rotate along with the animal, preventing cable tangling without the need for a traditional FoRJ. (Also see diagrams at the end of Plexon's optogenetics product guide.)
Overview of commercially available FoRJs
Doric Lenses' FoRJs
Single Rotary Joint (1x1 FoRJ)
The simplest version of these FoRJs provides a 1x1 transmission of light (1 optical fiber to 1 optical fiber). Doric Lenses announces a coupling efficiency (transmission) of 85% and less than 0.2 dB of variation in power transmission during rotations. This FoRJ works fine with fibers up to 1 mm and NA=0.50.
Intensity division (= beam splitting) can be performed at the level of the FoRJ by incorporating small prisms. Available beam splitting FRJs provide 1x2 or 1x4 transmission, allowing to simultaneously illuminate 2 to 4 brain regions using the same light source.
FoRJs can also incorporate small dichroic mirrors to perform wavelength division (= separation). For example, two wavelengths (say blue and yellow) can be combined into a unique fiber and then split into two separate fibers by the FRJ, allowing to simultaneously deliver one color to one brain region and the other color to another. Wavelength division can be combined with intensity division.
Prizmatix's Rotary Joint
Prizmatix's Rotary Joints combine excellent light transmission with extremely low torque.
A high NA (0.63) large core 1000um polymer (POF) fiber emerges from the LED to the Rotary Joint, from which on the other side is coupled one or more smaller core fibers (500um - 200um) to the cannula. Single or Y-shaped fibers available to stimulate two areas of the brain simultaneously with no losses.
Fiberoptic Rotary Joint + Electrical Commutator
Tucker Davis' ACO32 commutator
Motorized commutators are used routinely for chronic recordings of neuronal activity. These commutators start rotating when a certain torque has accumulated in the wire bundle, until the torque is reduced or cancelled. Tucker-Davis Technologies is a historical manufacturer of acquisition systems and accessories for chronic multiunit recordings. Their motorized commutator was recently modified to include a through hole which can accept an optical fiber, allowing to use the commutator in tandem with a passive FoRJ.
Doric Lenses' Electrical Rotary Joint
Doric's passive electrical rotary joint (ERJ) has a 7.5 mm through hole allowing to pass an optical fiber patchcord with a miniature fiberoptic connector. It also comes with accessories for attaching a 1x1 or 1x2 FoRJ and using it in tandem with the ERJ. The ERJ has a torque of 0.9 mNm and 1.8 mNm for 6 and 12 electrical contacts respectively. Dimensions are: 46 mm OD and 60 mm length. HARWIN M80-82612 connectors are used for electrical connection.
Electrical commutators for mounting miniaturized LED sources that rotate with the animal
- Plexon's electrical commutator for use with miniaturized LEDs that rotate along with the animal.
- Doric Lenses' optogenetics components
- Prizmatix's optogenetics toolbox
- Thorlabs' optogenetics solutions
- Optogenetic Components @ doriclenses.com
- In Vivo Optogenetics Toolbox by Mightex Systems, including multiwavelength fiber-coupled turn-key systems.
- Prizmatix extremely low friction rotary joint spinning for 30 seconds
- Deep-brain Calcium imaging and optogenetic stimulation on freely behaving animals.
- White Paper: "All-Optical Deep Brain Imaging & Stimulation Tools for In Vivo Neuroscience" has provided an overview of the existing all-optical imaging and stimulation tools, and compared the advantages and disadvantages of these techniques.