Study: Humans only have one sense, not five

Contrary to what has long been believed, humans do not have five senses but most likely one, says a U.S. neuroscientist from the Brandeis University in Massachusetts.

In a paper published in the journal Current Biology, associate professor of psychology Don Katz says he believes there is only one single sense, which he calls the chemosensory system.

For nearly a decade, Katz has been investigating the interconnection of smell and taste in rats. In a 2009 study, he showed that when rats lose their ability to taste, it alters their sense of smell. He published a paper two years later, suggesting that rats depend on smell as much as taste to determine what food they like.

“How things taste depends on a lot of other factors than what’s on the tongue. We think that taste and smell are part of one large system with two doors: the mouth and the nose,” Katz says.

In the new study, he showed what happened when the rat’s sense of taste is shut down. Using an optical probe, he turned off the brain cells in the animal’s primary olfactory cortex that process taste signals from the mouth. Katz found there was an immediate impact on the firing patterns of the neurons handling smell. He determined that the smell neurons were transformed so radically, the rat could no longer recognize familiar odors.

Citing previous studies which established that sound, touch, and sight are also inextricably connected, Katz came to a grand hypothesis: that all of a human’s senses belong to a single system.

Katz says it is meaningless, for example, to talk about the taste of food because taste is equally a function of what one’s sense on the tongue as it is of what is seen, touched, smelled, and heard. Humans do not taste food, but rather have an experience of it, he adds.

He likens the brain to a computer that is fed with an immense amount of data so it can generate a single, simplified finding. Information must be gathered through all the senses to enable the program to run. However, most people are not aware of this, and instead recognize the program’s final result. This is the illusion that only one sense is responsible for what humans experience, Katz explains.

He notes, however, that all this remains unproven. Katz plans to continue working on taste and smell in rats, which in the future may lead to a grand unified theory of the senses.

Demonstrating the connection of senses with one another, a 2009 study published in the journal PloS One, showed that the sense of touch allows humans to make a better connection between sight and hearing. According to the researchers, their findings should improve learning methods, both for children learning to read and adults learning foreign languages.

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