The hunt for a substance that can improve memory took a promising turn, as researchers said they had found a method that appears to reduce forgetting in rats, The Wall Street Journal reported Thursday.

According to a study published in the journal Nature, scientists from Mount Sinai School of Medicine in New York showed for the first time that a molecule that occurs naturally in the human brain during memory formation appeared to help rats enhance the strength and duration of some types of memories.

Researchers said that when the substance -- known as IGF-II, a protein-like molecule important for cell growth and development as well as tissue repair -- was blocked from the brain, the rats did not remember what they had learned.

The findings are notable in part because they showed improvement in an area of memory known as declarative memory -- the ability to remember places, facts and things. Declarative memory is affected in Alzheimer's disease and other forms of dementia, and researchers have long sought ways to improve or preserve it.

It is too early to say whether IGF-II will be useful in humans, but the substance may hold more promise than molecules that have been studied up to now, according to Elizabeth Phelps, a cognitive neuroscientist at New York University who studies human learning and memory. Phelps, who was not involved in the study, called the Nature research "rigorous" and thoroughly conducted.

One advantage of IGF-II is that it can cross the blood-brain barrier, so it could potentially be administered through the bloodstream or as a vapor through the nose, rather than injected directly into the brain. And because it exists in the body already, it is unlikely to be toxic.

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