With obesity continuing to grab the headlines, a study of what affects the motivation to feed contributes to a better understanding of how the brain responds to food stimuli.
The research suggests that a person's desire to eat, and when to stop eating, may be "all in their head".
A deeper understanding of which parts of the brain control the motivation to eat may lead to a greater understanding of what leads certain people to overeat.
With many critics keen to take the blame off a consumer's personal responsibility and heap it purely at the feet of the vending machine industry, the soft drinks industry, or the food industry in general, this research highlights just how multi-faceted and complicated the obesity issue may actually be.
The research study
For the new study, published in the August issue of the journal Neuron (Vol. 51, pp. 483-494), the scientists from Duke University Medical Center and Porto University studied the activity of rats' brain in a "natural" experimental situation with the animals allowed to decide when to start and end eating, and their brains analysed throughout entire hunger-satiety-hunger cycles.
By correlating the different stages of feeding (hunger - satiety - hunger) with brain activity, the researchers found that the majority of individual neurons only responded to a particular metabolic state (for example low or high glucose levels but not to both) within the full feeding cycle.
In contrast, Ivan de Araujo and his co-workers found that from the four brain areas studied (lateral hypothalamus, basolateral amygdale, insular cortex, and orbitofrontal cortex), the lateral hypothalamus seemed to be the most important for eating motivation, as its neural activity had the highest correlation with the changes within the feeding cycle.
'Injuries' motivate people to overeat
This observation agrees with previous research reporting that single lesions in this area of the brain could automatically lead to radical changes in appetite leading to hyperphagia (abnormally high food intake) or hypophagia (reduced food intake).
In other words, small injuries in this area of the brain could potentially motivate people to overeat, regardless of the taste, aroma or appearance of foods.
"This research contributes to a better understanding of the brain mechanics behind feeding stimulus, a particularly important issue in view of the current world epidemic of obesity," said Porto University spokesperson, Catarina Amorim.
One in two South African women and one in three South African men are overweight. That is 45% of the population – just 20% less than the world's fattest nation, the United States. - (Decision News Media, September 2006)
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