Our body is a mosaic of fungi. Some scientists think they could be influencing our brain

However, new evidence that microbes can invade the brains of animals like fish strengthens the notion that this could be happening in mammals – and perhaps even humans, Olm says. In a 2024 study, scientists labelled bacteria with tiny, fluorescent green molecules and added them to tanks housing salmon and trout. “After a week, you see these microbes making their way into the fish brain, lighting the fish brain up green,” Olm says, and curiously, “[the microbes] seemingly live there without huge consequences for these fish over their lifetime.”