“This strategy should allow us to identify and map brain circuits involved in complex behaviors related to sleep, depression, addiction, and anxiety,” says co-principal investigator Michael R. Bruchas, PhD, assistant professor of anesthesiology at Washington University.
“Understanding which populations of neurons are involved in these complex behaviors may allow us to target specific brain cells that malfunction in depression, pain, addiction and other disorders.”
For the study, Washington University neuroscientists teamed with engineers at the University of Illinois to design multicolored microscale, inorganic light-emitting diodes (µILEDs) that are just 6.45 microns (micrometers, or millionths of a meter) thick (thinner than a human hair) and and 50 × 50 µm square. The µILEDs are less than one-thousandth the size of conventional LEDs (typically 100 mm thick with lateral dimensions of 1 mm square).
The small sizes of µILEDs allow for spatially precise cellular-scale delivery of photons, highly effective
thermal management, reduced tissue damage, and minimized inflammation for prolonged use
This was the first application of the devices in optogenetics, which uses light to stimulate targeted pathways in the brain. The scientists implanted them into the brains of mice that had been genetically engineered so that some of their brain cells could be activated and controlled with light.
Although a number of important pathways in the brain can be studied with optogenetics, many neuroscientists have struggled with the engineering challenge of delivering light to precise locations deep in the brain. Most methods have tethered animals to lasers with fiber optic cables, limiting their movement and altering natural behaviors.
But with the new devices, the mice freely moved about and were able to explore a maze or scamper on a wheel. The electronic µLEDs are housed in a tiny fiber implanted deep in the brain. Moving freely is important to the device’s ability to activate the proper neurons, according to John A. Rogers, PhD, professor of materials science and engineering at the University of Illinois.