Re: What is the current research about the tongue having four taste areas?

Aloha, Alyssa,

Thank you for asking such an interesting question. Yes, the tongue does have distinct taste areas, but they are almost microscopic. That is why you might not have been able to detect specific tastes, according to the older notion of specific large areas being specific to the four tastes: sweet, sour, salt, and bitter.

There actually is a fifth taste, just recently described at the taste-receptor level...at the level of the taste pore. The taste is called "umami" and was described about 90 years ago by a Japanese physiologist (Kikunae Ikeda). He said the taste was due to one of the amino acids (portions of protein) called "glutamate." You can find a short news article about this in Science, volume 287, p. 799 (4 February 2000), or go on-line at www.sciencemag.org. The taste is found in protein-rich foods, such as soy sauce...we call it 'shoyu' here in Hawai'i..., yeast pastes, and meat broths.

Each taste is detected by a specialized organ called the taste pore. You have a lot of them on your tongue and around the lining of the mouth. They have different shapes (circumvallate, foliate, and fungiform), but apparently each taste pore can detect more than one taste, depending upon the nerve endings contained in the pore. There is a really good article in The American Scientist (the publication of Sigma Xi, an organization to which I belong), volume 82 (Nov/Dec 1994). It is written at a fairly advanced level, so you might want someone who knows something about physiology to help you go through it.

So, regarding your project, you might have to go more in-depth than just the 'old' idea of four distinct areas of the tongue mapping onto four tastes. Its a lot more complicated than that, especially with the fifth taste finally being confirmed at the molecular level. Good luck!

Reference:
Matsunami, H. et al. A family of candidate taste receptors in human and mouse, Nature, 404:601-4, 2000.