Researchers control brain circuits from a distance using infrared light
Imagine the brain as a giant switchboard covered with thousands of buttons, knobs, dials and levers that control aspects of our thought, emotions, behavior, and memory. .For more than a century, neuroscientists have been methodically flipping these switches on and off, alone or in combination, to try to understand how the machine works as a whole. But this is easier said than done.
"Optogenetics has been a transformative tool in neuroscience, but there are limitations on what can be done with existing techniques -- in part due to their reliance on light in the visible spectrum," Hong said."The brain is quite opaque to visible light, so getting the light to the cells you want to stimulate typically requires invasive optical implants that can cause tissue damage and skull-mounted fiber optic tethers that make it hard to study many kinds of natural behavior.
The new technique also relies on an engineered"transducer" molecule that can be injected into targeted brain regions to absorb and amplify the infrared light penetrating through the brain tissue. These nano-scale particles, dubbed MINDS , work a bit like the melanin in our skin that absorbs harmful UV rays from the sun, and are crafted from biodegradable polymers used to produce organic solar cells and LEDs.
In another key experiment, the researchers showed that MINDS could enable infrared stimulation of neurons through the entire depth of the mouse brain. They inserted TRPV1 channels into the dopamine-expressing neurons of the brain's reward centers, which are located near the base of the brain in mice, followed by an injection of MINDS into the same region.
"Like us, mice are a social species, but studying an animal's natural behavior within a social group is challenging with a head-mounted fiber-optic tether," Hong said."This approach makes it possible for the first time to modulate specific neurons and circuits in freely behaving animals.