Researchers from Brandeis University have revealed why food tastes wrong when the nose is clogged, as accurate taste perception relies on a functioning olfactory system.
Lead researcher and neuroscientist Don Katz showed that if the taste cortex in rats is inactivated when a rat first smells an odour, at least a food odour, then the rat subsequently will only recognize the food associated with that odour if the taste cortex is again inactivated.
"We discovered that rats use their taste system to smell with, so when you knock out the taste cortex, even for an hour, as we did, you alter their sense of smell," Nature magazine quoted Katz as saying.
The researchers added, "this is the only example of state dependency in neural circuit function of which we are aware."
During the study, researchers introduced a demonstrator rat that had just eaten chow flavoured with one of four spices to a subject rat, which then smelled the demonstrator rat's breath.
The subject rat was later offered two choices of chow: one dish with the same flavour previously consumed by the demonstrator rat and another with a different flavour.
The study shoed that subject rat reliably preferred the food that it had previously smelled on the demonstrator rat's breath the day before.
The researchers concluded that the social "smell test" of rat's breath is a good enough cue for rats to prefer one food over another.
At the outset they predicted that the rat's sense of smell would not be affected by changes in its taste system.
"Most surprisingly, the rats whose taste cortex was knocked out again the next day preferred the chow that they had experienced in an altered state, with no taste cortex.
"We discovered in this experiment that the sensory systems don't work in isolation from each other, said Katz.
"One part of the cortex takes direct input from the nose, and one part from the tongue, and while it's convenient to think that the nose and taste receptors operate independently, they don't," Katz added.
The findings appear in journal Nature Neuroscience.