Kids are wildly better than adults at most types of learning—most famously, new languages. One reason may be that adults' brains are “full,” in a way. Creating memories relies in part on the destruction of old memories, and recent research finds that adults have high levels of a protein that prevents such forgetting.

Whenever we learn something, brain cells become wired together with new synapses, the connections between neurons that enable communication. When a memory fades, those synapses weaken. Researchers led by Joe Tsien, a neuroscientist at the Medical College of Georgia, genetically engineered mice to have high levels of NR2A, part of a receptor on the surface of some neurons that regulates the flow of chemicals such as magnesium and calcium in and out of a cell. NR2A is known to be more prevalent in the brains of mammals as they age. The engineered mice, though young, had adult levels of NR2A, and they showed some difficulty forming long-term memories. More dramatically, their brains could barely weaken their synapses, a process that allows the loss of useless information in favor of more recent data.

A similar process may govern short-term memories as well. When you hear a friend ask for coffee, the details of her order don't just slip away in your mind—your brain must produce a protein that actively destroys the synapses encoding that short-term memory, according to a 2010 paper in Cell.

Much psychological research supports the idea that forgetting is essential to memory and emotional health [see “Trying to Forget,” by Ingrid Wickelgren; Scientific American Mind, January/February 2012]. Tsien's new work, published January 8 in Scientific Reports, suggests that older brains hold on to their connections more dearly—which helps to explain why learning is more laborious as we age and why memory trouble later in life so often involves the accidental recall of outdated information.

HOW TO INTENTIONALLY FORGET A MEMORY

Direct Suppression

Try to block out all thoughts of a certain memory.

Increases activity in the right dorsolateral prefrontal cortex , which mediates working memory and cognitive control.

, which mediates working memory and cognitive control. Reduces activity in the hippocampus, an area important for conscious recollection.

Thought Substitution

Try to forget by substituting the unwanted memory with a more desired one.