That bitter tincture a bunch of mice in a Columbia University lab recently gagged on could have been sweet nectar, or even just plain water. Why they took issue with the taste: For a study published in the journal Nature, scientists fiddled with their brain cells to make them think they were sensing an entirely different taste—meaning taste may be nothing more than a "fragile illusion," as the Washington Post puts it. "Taste, the way you and I think of it, is ultimately in the brain," lead author Charles Zuker explains in a press release. He notes that while there are specific receptors on the tongue to pick up the five distinct tastes (sweet, sour, bitter, salty, and savory "umami"), the signals transmitted by each receptor are picked up by discrete sets of brain cells—cells that Zuker says can be effectively hacked to alter a subject's perception of a taste. And that's just what Zuker and his team did to the lab mice via optogenics, which uses the power of light to "selectively activate and deactivate the neurons associated with sweetness and bitterness," per the Post.
Zuker compares it to pressing the keys of a piano: Press a certain key, get a certain sound. "But it doesn't matter how you press the key," he tells the Post. "You could use [a] finger, an elbow, a nose. It doesn't matter how we tweak the cells; if you tweak the right cells, you get the right signal." He says researchers saw that manifest in the lab when a mouse with a mouthful of water started gagging because scientists had "silenced" sweet-detecting neurons. "These experiments formally prove that the sense of taste is completely hardwired, independent of learning or experience," Zuker says, per ScienceAlert. Further research could eventually help people with eating and other disorders, he adds. And Zuker has even "sexier" goals in mind, per the Post. "If we could define the circuits involving courage, we could theoretically activate courage in the brain," he says. (Your lungs have taste buds, too, you know.)