Richard G. Petty, MD

Hunger and Memory

It’s always a good idea to see how new findings fit in with previous knowledge, and also to see if they make sense. We have previously met the hormone leptin, which is involved in decreasing appetite. Its twin is the hormone ghrelin. Discovered in 1999, ghrelin comes from some of the cells lining the stomach and acts in the hypothalamus to increase appetite. When the stomach is empty it is released into the circulation and travels to the brain where it activates receptors in many different regions. Some research has indicated that one of the reasons why gastric bypass surgery may be effective is because it reduces levels of ghrelin and therefore reduces appetite.

Research published in December 2004 showed that in healthy young men, sleep deprivation caused a decrease in leptin levels and an increase in ghrelin levels, which, as expected, was associated with an increase in hunger and appetite. This is one reason why getting less sleep than you need may cause you to gain weight.

A new study published in the journal Nature Neuroscience, has found an intriguing link between ghrelin and memory. I noticed that the BBC also picked up on this interesting story. Researchers at Yale have discovered that ghrelin acts in an ancient part of the brain known as the hippocampus: so named because it is shaped like a sea-horse. (As an amusing aside, the old German pathologists thought it looked like a silk worm, so that’s what they called it!) The hippocampus has a number of functions, but is most of all essential for learning new material.

The researchers showed that mice who lack the ghrelin gene had 25% fewer synaptic connections between their hippocampal neurons. They then did the next step, and injected normal mice with ghrelin. They promptly increased the number and density of their synaptic connections, which correlated with significant improvements in the animals’ performance on several tests of learning and memory.

So that means that a hormone produced by the stomach can control some brain functions, and this may represent a link between metabolism and the ability to learn. The more that we discover, the more we see the intimate interactions between the brain, intestines and heart.

This link makes good sense: we know that memory can be switched on and off by a range of factors. In order to help us come up with options for handling the environment and for remembering things to avoid, memory is often switched on at times of stress. Hunger is a form of stress, and it makes good biological sense that we might be more alert and better able to remember and to recall information when hungry. It stands to reason that this has enormous survival advantage. If our early ancestors had not had this hunger/memory link, they might well have died out in the competition for food.

This gives some credence to the old advice that it is best not to try to study or to take an exam on a full stomach. Just have enough food to make sure that you have ample fuel, and that you are not distracted by hunger pains.

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About Richard G. Petty, MD
Dr. Richard G. Petty, MD is a world-renowned authority on the brain, and his revolutionary work on human energy systems has been acclaimed around the globe. He is also an accredited specialist in internal and metabolic medicine, endocrinology, psychiatry, acupuncture and homeopathy. He has been an innovator and leader of the human potential movement for over thirty years and is also an active researcher, teacher, writer, professional speaker and broadcaster. He is the author of five books, including the groundbreaking and best selling CD series Healing, Meaning and Purpose. He has taught in over 45 countries and 48 states in the last ten years, but spends as much time as possible on his horse farm in Georgia.

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