Optogenetics Heightens Whisker Sensitivity in Mice

Researchers have heightened the sensitivity of mouse whiskers by using optogenetics to create gamma waves in the brain.

A team from Brown University used pulses of blue light to manipulate inhibitory interneurons in the primary sensory neocortex of the mice, generating a gamma rhythm. The primary sensory neocortex controls the mouse’s ability to detect faint sensations via its whiskers. Mice sometimes naturally produce a 40-Hz gamma rhythm in their sensory neocortex, according to the researchers.

The researchers said gamma waves could make typically difficult-to-perceive vibrations more vivid, though mice experiencing the gamma rhythm also appeared less able to detect more obvious sensations, even as they became more sensitive to subtler ones.

A gamma rhythm developed via optogenetics was found to make mice more sensitive to touch. Courtesy of Micheal Cohea/Brown University.

Mice experiencing the gamma rhythm were found more often to detect fainter stimuli with their whiskers than those that did not have the rhythm going in their brains. Study results showed that the whiskers on the first set of mice were about 20 percent more sensitive, the researchers said. Subjects showed increased sensitivity when the gamma rhythms began 20 to 25 ms before subtle sensations were presented.

“There were a lot of ways this experiment could have failed,” said Dr. Christopher Moore, an associate professor of neuroscience at Brown, “but instead to our surprise it was pretty decisive from the very first subject we looked at — that under certain conditions we can make a super-perceiving mouse. We’re making a mouse do better than a mouse could have done otherwise.”

The team’s hypothesis states that the gamma rhythm orders messages from pyramidal neurons into a more coherent and therefore stronger train.

A key implication from the findings is that the way gamma rhythms appear to structure the processing of perception is more important than the mere firing rate of neurons in the sensory neocortex. Mice became better able to feel not because of neurons’ activity, they said, but because they were entrained by a precisely timed rhythm.

“It’s not surprising that these synchronized bursts of activity can benefit signal transmission, in the same way that synchronized clapping in a crowd of people is louder than random clapping,” said researcher Joshua Siegle, a former graduate student at Brown who is now at the Allen Institute for Neuroscience in Seattle.

The work was funded by the National Institutes of Health. The research was published in Nature Neuroscience (doi: 10.1038/nn.3797).

For more information, visit www.brown.edu.