Implications for a hippocampal role in promoting obesity

A recent article published in the American Journal of Physiology reviewed how the brain regulates feeding behaviors. Humans are not the only species to eat food in spurts we like to call meals. Research suggests that this behavior may actually aid survival as it reduces exposure time to the environment and makes responding to fluctuations in the availability of food a bit easier to deal with. Dr. Marise Parent and colleagues at Georgia State University wanted to find out how your body determines when to initiate eating as well as how long the interval between meals should be.

Factors that contribute to when we begin eating include our own biological clock (I know mine is very regular when it comes to eating) and hormonal cues. Just like Pavlov's dogs, rats who are fed on a constant schedule, begin to anticipate the next meal resulting in changes of several hormones that regulate feeding and serve to prepare the stomach for the incoming meal.  These types of associations can even overcome the feeling of satiety, which is one reason we may overeat. This is a form of associative learning.

Dr. Parent and colleagues believe that this ability to override other signals lies within the hippocampus, the region of your brain that is associated with forming autobiographical memories such as where you spent last Thanksgiving, what you ate for dinner that night, when you ate it, etc. In fact, the hippocampus can receive nerve signals providing information about food stimuli from other parts of the brain that process signals about taste and hunger as well as information from the digestive tract. It also has receptors that can respond to several hormones related to feeding behaviors. In addition, the hippocampus can send signals to other areas of the brain that regulate the intake of energy, such as the hypothalamus. This makes it a relay station of sorts uniquely situated to control feeding behaviors like meal onset.

Lesions (i.e. injuries) of the hippocampus result in overeating, weight gain, and loss of the ability to differentiate between feeling full or hungry. Studies like these referenced to in the article suggest that the hippocampus may be important in diet-induced obesity as well as sustained obesity that can promote impaired memory formation. The authors speculate that energy dense foods and stress can impact the hippocampus and normal memory formation leading to shorter intervals between meals as well as increasing the frequency of meals and their size, which further damages the hippocampus causing a vicious cycle to develop as shown in figure 6 from their review article below.

Parent MBDarling JNHenderson YO. Remembering to eat: hippocampal regulation of meal onset. American Journal of Physiology. 306: R701-R713, 2014.

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