Researchers use miniature electronic device to tap into internal reward system of mice

Published on April 15, 2013 at 3:12 AM · No Comments

Using a miniature electronic device implanted in the brain, scientists have tapped into the internal reward system of mice, prodding neurons to release dopamine, a chemical associated with pleasure.

The researchers, at Washington University School of Medicine in St. Louis and the University of Illinois at Urbana-Champaign, developed tiny devices, containing light emitting diodes (LEDs) the size of individual neurons. The devices activate brain cells with light. The scientists report their findings April 12 in the journal Science.

"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 microscale (LED) devices thinner than a human hair. This was the first application of the devices in optogenetics, an area of neuroscience that 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 LEDs are housed in a tiny fiber implanted deep in the brain. That's 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.

"You want to be able to deliver the light down into the depth of the brain," Rogers says. "We think we've come up with some powerful strategies that involve ultra-miniaturized devices that can deliver light signals deep into the brain and into other organs in the future."

Using light from the cellular-scale LEDs to stimulate dopamine-producing cells in the brain, the investigators taught the mice to poke their noses through a specific hole in a maze. Each time a mouse would poke its nose through the hole, that would trigger the system to wirelessly activate the LEDs in the implanted device, which then would emit light, causing neurons to release dopamine, a chemical related to the brain's natural reward system.

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