Researchers like Dr. Davis argue that forgetting is an active mechanism that the brain employs to clear out unnecessary pieces of information so we can retain new ones. Others have gone a step further, suggesting that forgetting is required for the mental flexibility inherent in creative thinking and imagination.

A new paper, published Thursday in the journal Science, points to a group of neurons in the brain that may be responsible for helping the brain to forget. Akihiro Yamanaka, a neuroscientist at Nagoya University in Japan, and his team stumbled across the cells, known as melanin-concentrating hormone, or M.C.H., neurons, while studying sleep regulation in mice.

Unlike most of the brain’s neurons, which are active when animals are awake, M.C.H. neurons in the hypothalamus start firing electrical signals most actively when a sleeping animal is in a stage called R.E.M. sleep. This phase of sleep is characterized by rapid eye movement, an elevated pulse, unique brain waves and, in humans, vivid dreams. When the researchers tracked M.C.H. signals in mice, they found that the cells were suppressing neurons in the hippocampus, a brain region known to play a role in the consolidation of memory.

To evaluate the effects of the M.C.H. neurons on memory, the researchers used genetic tools to turn M.C.H. neurons on and off before mice performed some memory tests. First, the researchers presented the mice with a tiny plastic banana and a wooden toy to explore side by side. After each animal sniffed out both items, the researchers artificially activated or inhibited its M.C.H. neurons. Then they put each mouse back in the test cage, where one of the toys had been swapped out for a new item.

To the scientists’ surprise, “turning on” M.C.H. cells during the retention period worsened memory; the mice did not remember which toys they had already seen and smelled. They approached the familiar wooden or plastic toy with the same frequency as the new one. But mice that had their M.C.H. neurons artificially suppressed were more likely to play with the new item, indicating that they had formed stronger memories of the initial items and did not need to explore them again.