A magnetic rotary optical fiber connector for optogenetic experiments in freely moving animals

Abstract

Background Performing optogenetic experiments in a behaving animal presents a unique technical challenge. In order to provide an optical path between a fixed light source and a chronically implanted fiber in a freely moving animal, a typical experimental set-up includes a detachable connection between the light source and the head of the animal, as well as a rotary joint to relieve torsional stress during movement. New Method We have combined the functionality of the head mounted connector and the rotary joint into a single integrated device that is inexpensive, simple to build and easy to use. Results A typical rotary connector has a transmission efficiency of 80% with a rotational variability of 4%, but can be configured to have a rotational variability of 2% at the expense of lower transmission efficiency. Depending on configuration, rotational torque ranges from 14 - 180 μN*m, making the rotary connector suitable for use with small animals such as mice. Comparison with Existing Methods Benchmark tests demonstrate that our connectors perform similarly to commercially available solutions in terms of transmission efficiency, rotational variability, and torque but at a fraction of the cost. Unlike currently available solutions, our unique design requires a single optical junction which significantly reduces overall light loss. In addition, magnets allow the connectors and caps to “snap into place” for quick yet reliable connection and disconnection. Conclusions Our rotary connector system offers superior performance, reduced cost, and is easily incorporated into existing optogenetic set-ups.

Wirelessly powered, fully internal optogenetics for brain, spinal and peripheral circuits in mice

“…Such systems exploit the stable nature of the brain-skull interface, enabling persistent optogenetic modulation of identified neural populations. These systems have been refined over the past decade, such as by allowing fiber rotation during animal movements using optical and electrical commutators 2 and by improving the ease of attachment and detachment 7 . These tethered systems nonetheless impose significant constraints on experimental design and interpretation, both by requiring investigators to handle and physically restrain animals to attach an optical fiber before behavioral testing and by limiting the environments in which optogenetic experiments can be performed.…”

Evolution of optogenetic microdevices

“…56 Although a rotary connector seems to be an ideal solution for tethered experiments, it causes continuous pulling forces on the animal due to retraction of the cord, and frictional torques during animal rotations. Careful consideration of the animal species is important when using a rotary connector, as mice are able to withstand torques of up to 150 μN · m, while rats can exceed torque tolerations of >300 μN · m. 57 Therefore, optimization of pulling forces by the rotary connector is necessary to keep the cord taunt without causing unnecessary cord retracting stress to the animal. Despite achieving rotary optimization, tethering can still alter behavior and disrupt the naturalistic testing environment being sought, potentially confounding behavioral experiments.…”

“…Tethering the animal to the optogenetic system deviates from this natural setting as it restricts home-cage activity, spontaneous pain, wheel running, and freely moving social interactions. 73 With emerging technologies allowing biomedical devices to become smaller than previously imagined, researchers have designed devices that are small enough to be implanted subcutaneously, 57,74,75 some with only minor components exposed externally. These implantable devices allow the animal to perform measureable behavioral tasks while freely moving.…”

Optogenetic activation of nonhuman primate cortical and subcortical brain circuits highlights detection capabilities of MEG source imaging

“…We have developed a MEG-compatible optogenetic preparation in vervet monkeys that allows simultaneous optical stimulation and MEG recordings, along with associated local field potential (LFP) recordings from deep and superficial structures. Stimulation and LFP recordings were achieved with an optrode, which is a combined optical fiber/recording electrode 20,50 . Optogenetic techniques are well suited for use with MEG/MSI in that they are magnetically silent and allow for precise control over neural population potentials through the use and activation of virally-expressed, light sensitive ion channels 17 .…”