Emotional brain drives eating

Emotional brain drives eating
A hormone that signals satiety stimulates the brain's reward centers

A key signaling hormone that tells the brain when the stomach is full communicates with cognitive reward areas of the brain, according to a study published this week in Nature. The study is the first physiological demonstration that pleasure circuits play a key role in driving eating habits.

"The discovery that a biological signal activates this region of the brain [while eating] is very exciting," Steven Williams of Kings College, London, a coauthor on the study, told The Scientist.

Researchers have debated whether feeding behavior is dominated by the homeostatic demands of the hypothalamus or by reward-based signals sent from cognitive areas. Animal studies have suggested the former hypothesis, but psychologists have long known that reward plays a part in human eating patterns.

Rachel Batterham of University College London and colleagues examined this question by imaging the brains of subjects exposed to peptide YY (PYY), thought to be a satiety signal, after fasting and before a meal. After fourteen hours without food, subjects were given an intravenous drip of either the hormone, at levels that would mimic a 1500 kilocalorie meal, or a placebo for 90 minutes while their brain was scanned continuously. Then, they were given an unlimited meal. Each volunteer was tested twice, once with PYY and once with the placebo in a random order.

The subjects reduced the amount they ate by an average of 25 percent after receiving the hormone drip. The biggest change in brain activity in response to PYY occurred within the orbitofrontal cortex, a region implicated in emotional and reward processing. The hormone also activated the brain stem and hypothalamus, but to a lesser extent.

The link between orbitofrontal cortex activity and PYY infusion was unexpected, said Batterham. The researchers "were really surprised that the change in activity within this brain region predicted how much food the volunteers subsequently ate," she said. "The greater the change, the less they ate."

"We've known that people with lesions in the orbitofrontal cortex of their brains tend to have problems controlling their food consumption, but we never knew to what extent it was involved," said Williams

When volunteers received the placebo rather than PYY after fasting, the major change in activity occurred instead in the hypothalamus, and was correlated to how much they then ate.

"One possible explanation for these results is that when people are fasted, their drive to eat comes predominantly from more primitive brain centres. When they have been fed, the drive comes from the anticipated pleasure or value of the food," Paul Matthews of Imperial College, London, who did not participate in the study, told The Scientist via Email.

"I think one of the most interesting things about the paper is that it shows how a gut hormone can regulate the domain of neural signal processing that we use," Michael Cowley of the Oregon National Primate Research Center, who did not participate in the study, told The Scientist. "It can switch us from homeostatic processing to reward processing and back again."

He noted that the reward signaling pathway could provide novel targets for treating obesity and eating disorders.

Matt Kaplan
mail@the-scientist.com


Links within this article:

R.L. Batterham et al, "PYY modulation of cortical and hypothalamic brain areas predicts feeding behaviour in humans," Nature, October 15, 2007.
http://www.nature.com

Steven Williams
http://www.iop.kcl.ac.uk/staff/profile/?go=10917

H.R. Berthoud, "Interactions between the "cognitive" and "metabolic" brain in the control of food intake," Physiology & Behavior, January 12, 2007.
http://www.the-scientist.com/pubmed/17307205

Rachel Batterham
http://www.ucl.ac.uk/medicine/diabetes/staff/rb.html

J. F. Gautier, et al, "Effect of satiation on brain activity in obese and lean women," Obesity Research, November, 2001.
http://www.the-scientist.com/pubmed/11707534

H. Black, "Mother love and the brain," The Scientist, April 12, 2004.
http://www.the-scientist.com/article/display/14580/

Paul Matthews
http://www1.imperial.ac.uk/medicine/people/p.matthews/

Michael Cowley
http://onprc.ohsu.edu/discovery/dspScientistsItem.cfm?doc_id=124

S. Blackman, "The enormity of obesity," The Scientist, May 24, 2004.
http://www.the-scientist.com/article/display/14698/