Washington, Mar 7 : Ever wondered why you can't resist yourself from walking into a bakery after seeing chocolate- frosted donuts from the store's window? Well, the culprit is not lack of self-control but the brain.
New research from Northwestern University's Feinberg School of Medicine reveals how hunger works in the brain and the way neurons pull your strings to dive for the edible items.
In the study, subjects were tested twice - once after gorging on up to eight Krispy Kreme donuts until they couldn't eat anymore, and on another day after fasting for eight hours.
In both sessions, people were shown pictures of donuts and screwdrivers, while researchers examined their brains in fMRI's.
When the subjects saw pictures of donuts after the eating binge, their brains didn't register much interest. But after the fast, two areas of the brain leaped into action upon seeing the donuts.
First, the limbic brain - an ancestral part of the brain present in all animals from snakes to frogs to humans - lit up like fireworks.
"That part of the brain is able to detect what is motivationally significant. It says, not only am I hungry, but here is food," said senior author Marsel Mesulam, M.D., the Ruth and Evelyn Dunbar Distinguished Professor of Psychiatry and Behavioral Sciences at the Feinberg School and a neurologist at Northwestern Memorial Hospital.
Next, the brain's spatial attention network shifted the hungry subject's focus toward the new object of desire - in this case the donuts.
"If we didn't have this part of the brain, every time you passed by a bakery you would have no control over your eating. If your nerve cells fired every time you smelled something edible, then you'd eat all the time, not just when you're hungry," said Mesulam.
"There's a very complex system in the brain that helps to direct our attention to items in our environment that are relevant to our needs, for example, food when we are hungry but not when we are full," said Aprajita Mohanty, a post-doctoral fellow at the Feinberg School.
Mesulam noted the research demonstrates how our brain decides what to pay attention to in a world full of stimuli - not just sweets.
"If you are in a forest and you hear rustling, the context urges you to pay full attention since this could be a sign of danger. If you are in your office, the context makes the identical sound less relevant. A major job of the brain is to match response to context," said Mesulam.
The study is published in the journal Cerebral Cortex.