Injectable optoelectronics with wireless control

The ability to wirelessly control neural circuitry has been a long-standing goal in neuroscience. Recent advances have put this goal in site using optogenetic approaches. In 2011, multiple groups presented the first attempts at making wireless light delivery application for optogenetics (Iwai et al., 2011; Wentz et al., 2011). These advances, however, were constrained to particular environments or apparatuses to power the devices. The radiofrequency power scavenging approach presented in Kim et al., 2013 frees the experimenter from these constraints. In the recent report, the Bruchas (Washington University at St. Louis) and Rogers (University of Illinois at Urbana-Champaign) labs present ultrathin, microscale optoelectronics and sensors that can be used for the optogenetic manipulations. Unlike other wireless approaches this system can be used with any behavioral apparatus or paradigm, which should allow researchers to explore more complex behaviors while perturbing neural circuitry.

The wireless µILED devices can incorporate wired cellular-scale components that can all be inserted into the brain using a combination of a silk-based biodissolvable adhesive (Kim et al., 2010) and an injection needle similar in concept to electrode delivery presented previously (Kozai and Kipke, 2009). These components include, but are presumably not limited to, temperature sensors, electrodes for extracellular recordings, and photodetectors. The injection needle strategy allows the light sources and other components to be extremely thin and still maintain the ability to penetrate the brain. This thin design appears to reduce the inflammatory glial responses and lesion size compared to conventional fiber optic or cannula approaches.

For light delivery, the devices are powered using a strategy that that scavenges and rectifies energy for radiofrequency signals. As highlighted in a previous blog post and relevant manuscript (Voigts et al., 2013), the weight of any device will impact mouse behavior and the maximum weight a mouse can bear on its head is in the range of ~3g. To accomplish the wireless power scavenging, Kim et al (2013) have devised two versions of a removable headstage. The first is based on commercially available printed circuit boards and weighs ~2 g, the second is a circuit printed on polyimide film to reduce the overall weight to ~700 mg. The authors demonstrate the use of these wireless, light-delivery systems by stimulating dopamine neurons of the ventral tegmental area to drive reward-related behaviors. Importantly, once fabricated the use of these µILED devices are broadly accessible to nearly any laboratory, including those without access to advanced optical setups, using a wired connection to a traditional function generator or microprocessor equipped with transistor-transistor logic (TTL) signals.

Extending optogenetics to different, non-neural organ systems and behavioral assays has been somewhat limited by the use of fiber optics for light delivery. The ability of these unconventional devices to afford minimally invasive operation in the soft tissues of the brain provide opportunities for integration in other organ systems, such as the vascular and cardiac systems.

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