Brain's taste secrets uncovered by US scientists

The brain has specialist neurons for each of the five taste categories - salty, bitter, sour, sweet and umami, a discovery that could settle years of debate on how the brain perceives taste.
The Columbia University team showed the separate taste sensors on the tongue had a matching partner in the brain.
The scientists hope the findings could be used to help reverse the loss of taste sensation in the elderly.
Each of the roughly 8,000 taste buds scattered over the tongue is capable of sensing the full suite of tastes.
But specialised cells within the taste bud are tuned to either salty, bitter, sour, sweet or umami tastes.

When they detect the signal, a message is sent to the brain, scientists said.

Researchers at Columbia University engineered mice so that their taste neurons would fluoresce when they were activated. They then trained their endoscopes on the neurons deep at their base of the brain.
The animals were fed chemicals to trigger either a salty, bitter, sour, sweet or umami response on the tongue and the researchers monitored the change in the brain.
They found a "hard wired" connection between tongue and brain.
"The cells were beautifully tuned to discrete individual taste qualities, so you have a very nice match between the nature of the cells in your tongue and the quality they represent [in the brain]," Prof Charles Zuker told the BBC News website.

It scotches the alternative idea that brain cells respond to multiple tastes.
Zuker said: "In the ageing population, they don't enjoy eating anymore, you cannot believe how devastating this is.
"We believe that is a reflection of the taste cells in the tongue," he said.
Stem cells in the tongue produce new taste cells every fortnight. However, this process becomes weaker with age.
"These findings provide an interesting avenue to help deal with this problem because you have a clear understanding of how taste is functioning so you could imagine ways of enhancing that function," Zuker said.
This could include ways of making the existing cells more responsive so they sent a stronger signal to brain.

The study, published in the journal Nature, should settle years of debate on how the brain perceives taste, the report said.