Imagine the following: the sight of a flaming red-orange sunset, the smell of cinnamon lingering inside a pastry shop, the sounds and thrills of a Skrillex concert, the taste of your mom's home-cooking, and the touch of a lover who is holding your hand.
When we were younger, we were taught that most of us (excluding those with disabilities) experience the world through our five senses. We relish every sensation and add them to our treasure trove of memories.
But what if someone told you that what you know about your senses may be scientifically inaccurate?
Don Katz, a neuroscientist who spent a decade studying the interconnection of the sense of smell and taste in rats, believes that instead of the well-known five senses, humans actually have a unified system that contains all of them.
Switching Off the Gustatory Cortex
Six years ago, Katz and his colleagues published a paper in the journal Nature Neuroscience describing how the part of the brain that controls a person's gustatory senses affects the brain's olfactory center.
To prove their hypothesis, the group used a technique called optogenetics to switch off a rat's chief gustatory cortex. The method allowed researchers to manipulate the rat's neurons with light.
After a different rat was fed with a banana, scientists made the modified rat smell its breath. The modified rat was presented with the option to eat a banana or an avocado.
The rat chose to take and consume the banana, because it identified the smell from the other rat. The rat's recognition indicated that it was safe to eat the bananas.
When the gustatory system was switched on again, the rat chose between both the avocado and the banana.
This led Katz and his team to believe that rats utilize their gustatory system for smelling. Turning off the rat's sense of taste changed their sense of smell because foods smell differently when the gustatory sense is unavailable to supply sensory input, they said.
This Time, it's the Olfactory Cortex
In the new study which is featured in Current Biology, Katz and his team further tested their hypothesis.
Again, they used optogenetics to shut down certain neurons in the rat's brain. This time, they switched off neural cells associated with taste, which are found in the rat's olfactory cortex.
The effect of the switch to the way the olfactory neurons fired was so significant that the animal forgot even the most usual scents.
Katz explained that how olfactory neurons react to scents or the "codes" for those odors is dependent on whether the gustatory system is unaffected.
He said that after ten years of research, he now thinks that asking people how food tastes or smells like is futile. Instead, the right question is asking how the experience of consuming the food is, especially because the sense of smell and the taste are codependent on one another.
One Big Chemosensory System
Katz described it this way: individually, the sense of taste and the sense of smell are only two separate doors to one big, single house. Both these senses are only one single system with two sense organs, he said.
The neuroscientist thinks that an intimate and intricate link between taste and other conventionally-defined "sensory systems" is in service of an animal or human's need to learn and act upon the connection between what an object smells, feels, tastes, sounds, and looks like.
However, despite all the evidence that Katz had gathered, his single-sense or chemosensory system theory has yet to be proven.
With that, Katz and his team are looking forward to more research in the future.
"We are continuing to examine how activity in many circuits determines how taste and smell input are handled, how this plays out through time - both real time and learning time - and the implications for perception," explained Katz.
If successful, then perhaps, in the not-so-distant future, we may finally be teaching children a fascinating theory about the unified and all-encompassing chemosensory sense.
Photo : Allan Ajifo | Flickr
