The researchers presented 24 normal-weight participants with photos of hundreds of different types of food, as well as pictures of kitchen utensils, all the while recording their brain activity using electroencephalography (EEG).
The participants thought their task was to indicate as fast as possible whether each photo, presented for just half a second, showed food or a kitchen utensil. In fact, the researchers were interested in whether the brain activity of the participants differed according to whether a high or low fat food had been presented.
The advantage of EEG over brain imaging techniques like fMRI, is in the level of time-related detail it can provide. In this case, Toepel's team were able to show that high-fat food led to distinct patterns of brain activity relative to low-fat food, during two discrete time periods: 160-220ms and 330-370ms after presentation of the food.
The speed with which the fat content of food was discriminated by the brain is similar to that shown for other fundamental categories such as for living vs. non-living things. Because the participants were distracted by the task involving kitchen utensils, the results further show that this discrimination between high and low-fat foods occurs automatically.
Areas of the brain that showed sensitivity to food fattiness were temporo-parietal regions during the first time period and the pre-frontal cortex during the second time period. The first time period probably relates to rudimentary analysis of the fattiness category, and the second probably relates to decision making.
"Enhanced activation in prefrontal cortices has also been related to syndromes of eating disorders," the researchers explained. "Thus, the network identified during this second stage points to the role of this categorization phase in the decision-making process on food choices based on their energetic value."
U TOEPEL, J KNEBEL, J HUDRY, J LECOUTRE, M MURRAY (2009). The brain tracks the energetic value in food images. NeuroImage, 44 (3), 967-974 DOI: 10.1016/j.neuroimage.2008.10.005
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