David Artis, an immunologist and microbiologist at Weill Cornell Medicine in New York City, wondered whether gut bacteria played any role in the learning and forgetting responses. He and colleagues treated mice with antibiotics to totally rid them of the bacteria in their gut, collectively known as the microbiome. They then played a tone and right after gave the mouse a mild shock, doing this multiple times.
All of the animals quickly learned to associate the noise with pain, freezing when they heard the sound. But only mice with normal microbiomes eventually forgot the connection: By 3 days, the noise no longer affected them most of them, whereas
the antibiotic-treated mice still reacted, the team reports today in Nature.