Since its advent in 2005, a technique called optogenetics has made it vastly easier to link neural activity with behavior and to understand how neurons and brain regions are connected to each other. Neuroscientists just pick the (animal) neurons they’re interested in, genetically engineer them to express a light-responsive protein, and then stimulate them with the right type of light. This technique can be used to inhibit or excite a select subset of neurons in living, breathing, moving animals, illuminating which neural networks dictate the animals’ behaviors and decisions.
Taking advantage of work done in miniaturizing the optogenetic hardware, researchers have now used optogenetics to alter the activity in parts of the brain that influence social interactions in mice. And they’ve exerted a disturbing level of control over the way the mice interact.
A big limitation for early optogenetic studies was that the wires and optical fibers required to get light into an animal’s brain also get in the animals’ way, impeding their movements and potentially skewing results. Newer implantable wireless devices were developed about five years ago, but they can only be placed near certain brain regions. They’re also too tiny to accommodate many circuit components and receiver antennas, and they have to be programmed beforehand. Pity the poor would-be mind controllers who have to deal with such limited tools.
Enter John Rogers, founding director of the newly endowed Center on Bio-Integrated Electronics at Northwestern University. His lab recently invented multilateral optogenetic devices that can be implanted into the heads or backs of animals as small as mice. The devices can receive instructions on different channels, so they allow researchers to independently and simultaneously modulate neuronal activity in different brain regions of one mouse or in different mice within the same enclosure. The devices are controlled wirelessly from a PC, and researchers can alter the instructions to them in real time as an experiment is proceeding.
After confirming that the implanted devices neither affected nor were affected by a mouse’s movements and that they didn’t damage any of the mouse’s tissues or physiology, the scientists in Rogers’ group popped a light-responsive protein into some dopaminergic neurons in the ventral tegmental areas of some mice. These regions are linked to reward processing. The researchers then implanted their new device under the skin of the transgenic mouse.
The first tests confirmed results attained in previous optogenetic experiments: implant-affected mice that got a dopamine-fueled reward via a burst of light hovered on the side of the enclosure where the system was programmed to produce light. So far, so good. Next, since the researchers knew that dopamine promotes social behavior, they wanted to see if the light stimulation made the implanted mice choose to hang out near another mouse rather than a toy one. They did.
To put the system to use, the researchers tested an idea from a number of earlier studies suggesting that mice that socialize together tend to have synchronized activity in a specific area of their brains. The new optogenetic hardware provided a way to artificially create that synchrony.
So the researchers generated “synchronized interbrain activity” by stimulating two mice with 5-Hz tonic (continuous) stimulation for five minutes and desynchronized activity by stimulating other pairs of mice with 25-Hz bursting stimulation for five minutes. About twice as many of the synchronized mice chose to socialize with each other—grooming, sniffing, etc.—as the desynchronized mice did. When two mice were synchronized into a 5-Hz pair and a third mouse got the 25-Hz burst, the pair shunned the desynchronized third. The researchers conclude that “imposed interbrain synchrony shapes social interaction and social preference in mice.”
The Rogers Research Group’s home page is subtitled “science that brings solutions to society.” The lab has developed wearable wireless devices that seamlessly track vital signs of neonates in the NICU, record electrical activity in the brain, and detect and monitor symptoms of COVID-19. And that was only in the past year.
So before you let your mind go to dark places—about brainwashing and goose-stepping and everyone forever staying sequestered in their ideologically homogeneous Facebook silos—just remember that Dr. Rogers is using his powers for good. Also, this work was done in genetically engineered mice.
Nature Neuroscience, 2021. DOI: 10.1038/s41593-021-00849-x