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The neurohormone ghrelin, best known for its role in appetite and energy metabolism, also influences learning and memory, according to a new study in Nature Neuroscience. Specifically, Sabrina Diano of Yale University School of Medicine and her colleagues found that high levels of ghrelin in rodents can alter hippocampal morphology and improve performance on memory and learning tasks. This pattern may have provided an evolutionary advantage, the authors speculate, by boosting memory skills during food searches when animals are hungry. . .

Learning and memory may be enhanced by high levels of ghrelin during food deprivation because animals need increased cognitive skills to track down food sources, Diano told The Scientist.

However, Steiner cautioned that the researchers injected a concentration of ghrelin that’s several orders of magnitude above what would be found in the bloodstream, which means that normal fluctuations in ghrelin due to food deprivation may have nothing to do with learning or memory.

Ghrelin is also produced in the brain, suggesting that differences seen in ghrelin knockouts may be due to disrupted ghrelin expression there, rather than in the stomach, Christian Broberger of the Karolinska Institute in Stockholm, also not a co-author, told The Scientist in an Email.

It’s also a bit surprising that ghrelin would have positive effects on learning and memory, according to David E. Cummings of the University of Washington, because the hormone insulin has also been shown to improve learning and memory, and ghrelin and insulin usually have opposite effects.

Even if ghrelin fluctuations do not normally influence memory, Steiner said, high doses of ghrelin or an analog could still make good candidates for treatment of age-related memory problems. “I’m more enthusiastic about the pharmacologic and pharmacotherapeutic implications of the study than I am about whether or not the physiological arguments that they developed are true.”