Wetenschap - 5 april 2012

Scanning for taste

- Seeking the region of the brain that does ‘tasty'.
- First Wageningen MRI studies in nutrition.

Alex's feet are going up and down; he's nervous. He's been lying completely still for some 20 minutes in the MRI scanner, his head fixed in an uncomfortable position. The thrumming machine has been mapping his brain. Yet Alex is not ill; he is a test subject. In his brain, and the brains of dozens of others, nutrition researchers are hunting for the regions of the brain where we experience ‘revolting' and ‘tasty'.
Brainfood is one of the first experiments using the new MRI scanner in the Gelderse Vallei hospital in Ede. The scanner was purchased in May 2011 by the virtual equipment centre CAT-AgroFood. It offers new scope not only for brain science but in other areas too, such as monitoring stomach fat. In addition, the similarly new olfactometer administers odours in controlled doses. ‘Are you ready to go on?', Iris van den Bosch, trainee research assistant in the Human Nutrition department, asks Alex over the intercom. She restarts the scanner and, at the same time, the gustometer, as it is called. This looks like a computer table with a number of fat injection needles screwed on to it. In turn, these squirt two millilitres of liquid into a long tube that reaches into Alex's mouth. ‘Taste' or ‘Swallow' commands the computer programme, via the screen that Alex can see.
For her experiment, Van den Bosch sought test subjects who either love or detest grapefruit juice. For a couple of seconds at a time they taste alternately sips of water and grapefruit juice. The scanner records which regions of the brain are using more oxygen, meaning they are activated. The brain areas that lights up in people who love grapefruit juice are different from the areas that lights up in people who find grapefruit juice revolting.
So many test subjects
Research into the brain's processing of taste and odours is still in its infancy, tells Van den Bosch. In the past, attention was devoted mainly to memory, attention and sight: functions related to Alzheimer's disease and other serious medical disorders. Such connections also made it easier to find funding. Only over the last ten to fifteen years has there been more interest in the perception of taste and odours.
Nonetheless, there are experiments that Van den Bosch can build on. In 2001 Canadian scientists had their test subjects lie in a PET scanner and eat so much chocolate that they became nauseous. The researchers observed how their brain activity changed as eating with pleasure turned into eating with loathing.
Another study examined brain activity under the influence of sugar water and a bitter quinine solution. Van den Bosch is repeating these experiments to see whether he gets the same results. It will be interesting to compare these findings with those of the grapefruit study. This is because the taste of grapefruit juice is determined by personal preference, whereas our love of sugar and natural aversion to quinine have their roots in evolution. The question is whether our brains respond to these stimuli in the same way.
Van den Bosch is confident that she will be able to provide definite answers to such questions. ‘We have a ridiculously large number of people for an MRI study,' she says. Whereas most studies include only about 15 test subjects, she found 20 grapefruit lovers and 20 people who hate the stuff. This promises an excellent basis for statistical correlations.
Space Odyssey
After the experiment Van den Bosch uses a brain map to explain to her test subjects how they process taste. ‘The signals from your tongue are received via the brain stem and travel on to the thalamus to be processed further.' In fact, they already have some ideas about the location of our reactions to nasty and pleasant tastes. These are probably situated in different areas of the brain, one for pleasure and one for the avoidance of unpleasant tastes.
After 50 minutes in the MRI scanner, Alex is somewhat dazed. ‘It is actually a bit like being in a capsule. Like in a space odyssey.' It turns out that it is not easy to swallow while lying on your back. And he's had no breakfast because he had to do the experiment on an empty stomach. 'My stomach was rumbling while I was lying in the scanner.' Nevertheless he is enthusiastic and ponders cheerfully the hypothesis being tested. ‘I'd like to participate again,' he decides, ‘only next week would be a little too soon.'