We now know that gut microbes are part of this axis, in both directions. Since the 1970s, a trickle of studies have shown that any kind of stress – starvation, sleeplessness, being separated from one’s mother, the sudden arrival of an aggressive individual, uncomfortable temperatures, overcrowding, even loud noises – can change a mouse’s gut microbiome. The opposite is also true: the microbiome can affect a host’s behaviour, including its social attitudes and its ability to deal with stress.
