'This brain signal tells us how much to eat at buffets'

Scientists have found a brain region that might help people to make quick calculations about which dishes to try and how much to take of each at holiday buffets and potlucks.

The researchers at Johns Hopkins University in the US found robust neural activity in rats related to food choice in a previously overlooked part of the brain.

The finding, published in the journal Nature Communications, suggests this brain area could be key to developing therapies and treatments to encourage healthy eating.

"We found a region in the brain that reflects our perception of food in a strikingly dominant way," said David Ottenheimer, a graduate student at Johns Hopkins University.

"The level of brain activity we saw exceeded our expectations by far," Ottenheimer said.

The research team wanted to know how the brain determines what and how much to eat when someone has several good food options.

It is a situation people face daily, if not at buffets or potlucks, then when looking over restaurant menus or at what is in the refrigerator, researchers said.

When someone is considering either mac and cheese or mashed potatoes, the brain must quickly determine which of those quite similar choices -- both tasty, both treats, both carbs -- would be most rewarding, they said.

Even if we can have both, Ottenheimer said, the dish that's the favourite will likely be eaten faster and with bigger bites.

Researchers gave rats two similar sugary drinks. The rats preferred the one made with sucrose over the one with maltodextrin, and when they received sucrose, they'd lick it faster.

Over several days, the rats were given either one drink or the other.

The team mapped the rats' brain activity precisely at the moment the animals realised which drink they had gotten, pinpointing the neurons that registered the excitement for sucrose, and the disappointment for maltodextrin.

The activated neurons were in an area called the ventral pallidum, a spot long associated with reward and pleasure perception, but thought to be in more of a secondary role.

The team presented rats with a different set of options --either the maltodextrin drink or plain water. In this scenario, when rats got maltodextrin, ventral pallidum neurons fired liked they had for sucrose.

This suggests the brain area is making context-dependent decisions, zeroing in on the best food option at any given time.

"Because the signalling by ventral pallidum neurons changes immediately when the rat changes his ranking of which flavour is his favourite, we see this response as providing a real-time readout of what you like best from currently available options," said Patricia Janak, a professor Johns Hopkins University.