It is more or less a given that at some point in your life, you have encountered the taste map -- a map of the tongue predicated on the idea that different regions of your tongue taste different flavours.
It's not true; the 1901 theory was debunked pretty solidly in 1974, and has continued to be debunked since. But the exact relationship between the taste cells within the taste bud and how we perceive taste still remained something of a mystery, said Professor Seok-Hyun Yun from Harvard Medical School.
For the first time, a global team including Professor Yun, biomedical engineer Dr Steve Lee of the Australian National University's Research School of Engineering and Assistant Professor Myunghwan Choi, from the Sungkyunkwan University in South Korea, have conducted live imaging of the tongue while tasting is in process.
The human tongue contains over 2,000 taste buds, each of which can distinguish at least five basic tastes: sweet, salty, sour, bitter and umami -- a Japanese word that describes a meaty or savory taste. Using a specially designed microscope system, the team watched live taste cells on a mouse's tongue capture and process molecules with different tastes.
"With this new imaging tool we have shown that each taste bud contains taste cells for different tastes," Professor Yun said.
They also found that those molecules didn't have to be touching the surface of the tongue; the cells also reacted to molecules in blood circulation.
"We were surprised by the close association between taste cells and blood vessels around them," said Assistant Professor Choi. "We think that tasting might be more complex than we expected, and involve an interaction between the food taken orally and blood composition."
To image the process of tasting, the team shone a bright infrared laser on the mouse's tongue. This caused parts of the tongue and flavour molecules to fluoresce. This activity was was captured by a technique known as multiphoton intravital microscopy, which allows dynamic biological processes to be captured at high resolutions and speeds.
Using this technique, the team was able to see individual taste cells within each taste bud, and blood vessels up to 240 microns underneath the surface of the tongue, capturing the process of tasting in action. That doesn't mean, however, that the process is still fully understood. The next step in the research is to image the brain while tasting is in process to see the effect the sensation has on neurons.
"Until we can simultaneously capture both the neurological and physiological events, we can't fully unravel the logic behind taste," Dr Lee said.