How Many Senses Do Humans Have? It Could Be As Many As 33

Humans have five senses, right? At least, that’s what Aristotle said back in 350 BCE. And despite the fact that several of the famed Ancient Greek philosopher’s scientific theories were proven more than a bit wrong, his idea about the senses has persisted – and now modern science is challenging him once again.

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The late Professor Sir Colin Blakemore, a world-renowned neuroscientist, wrote back in 2014 that humans could have anywhere up to 33 senses. If the last few years of research are anything to go by, that doesn’t seem like much of a stretch at all. So, what’s the latest on what there is beyond sight, touch, smell, hearing, and taste?

The “neurobiotic” sense

Back in July, a study led by researchers at the Duke University School of Medicine concluded that there was a new sense that linked up microbes living in the gut with the brain, dubbed the “neurobiotic sense”. 

“We were curious whether the body could sense microbial patterns in real time and not just as an immune or inflammatory response, but as a neural response that guides behavior in real time,” said co-senior author Diego Bohórquez in a statement.

That curiosity led Bohórquez and colleagues to flagellin, a protein typically found in flagella – those wiggly tail-like structures that some bacteria use to propel themselves about. Bacteria like these that live in the gut shed flagellin when there’s food around, and the study found that the released protein was detected by specialized gut sensory cells called neuropods via a receptor called TLR5.

These neuropods, the authors suggest, send off a signal to the brain that suppresses appetite; when mice missing TLR5 were given a small dose of flagellin and food after having fasted, they didn’t stop eating, and gained weight. This implies that the signaling was no longer occurring.

While the research doesn’t necessarily directly translate to humans, as it was carried out in mice, it’s opened up an interesting new avenue of possibilities.

“Is there a way we can use microbes to, maybe subliminally, have us make better decisions about the food we’re eating?” posed study co-senior author M. Maya Kaelberer in another statement.

Remote touch

Also this year, researchers discovered that we have something in common with shorebirds other than a love of the seaside: a sense known as remote touch.

Birds like sandpipers and plovers have receptors in their bills that are capable of picking up on minute vibrations in the sand as they move through it, allowing them to detect prey hidden below. We might not have bills, but we do have hands – and it seems like that’s enough to do the same job.

In what the authors said is the first study of remote touch in humans, they had volunteers move their fingers through some sand in an attempt to detect a hidden object – a cube – before coming into direct physical contact with it.

It turns out that not only were the human volunteers capable of detecting the cube, but also did so with a surprising level of precision – 70.7 percent at a distance of 6.9 centimeters (2.7 inches).

That’s over 30 percent more precise than the robots the team trained to carry out the same task, but that doesn’t mean the robot research wasn’t useful. The combined knowledge gained from both experiments could be put to use in all kinds of interesting ways, the authors say.

“The discovery opens possibilities for designing tools and assistive technologies that extend human tactile perception,” said study author Zhengqi Chen in a statement.

“These insights could inform the development of advanced robots capable of delicate operations, for example locating archaeological artifacts without damage, or exploring sandy or granular terrains such as Martian soil or ocean floors. More broadly, this research paves the way for touch-based systems that make hidden or hazardous exploration safer, smarter, and more effective.”  

A new approach

It’s all well and good finding these new senses, but Blakemore argued that where historical research into the senses went wrong was looking at each of them in isolation.

“Studying isolated senses is misleading,” he wrote. “Everyday experiences, such as watching a film or eating a meal, involve different senses working together.” Blakemore gives the example of our experience of flavor, which relies not only on taste, but also what we smell, see, touch, and hear.

“These effects demonstrate that multisensory interactions are the rule rather than the exception,” Blakemore continued. “The multisensory nature of perception will be understood only through philosophers and cognitive neuroscientists working together to re-evaluate how the senses work together.”

H/T The Conversation.