Hundreds of millions of years ago, at a time when back-boned animals were just starting to crawl onto land, one such creature became infected by a virus. It was a retrovirus, capable of smuggling its genes into the DNA of its host. And as sometimes happens, those genes stayed put. They were passed on to the animal’s children and grandchildren. And as these viral genes cascaded through the generations, they changed, transforming from mere stowaways into important parts of their host’s biology.

One such gene is called Arc. It’s active in neurons, and plays a vital role in the brain. A mouse that’s born without Arc can’t learn or form new long-term memories. If it finds some cheese in a maze, it will have completely forgotten the right route the next day. “They can’t seem to respond or adapt to changes in their environment,” says Jason Shepherd from the University of Utah, who has been studying Arc for years. “Arc is really key to transducing the information from those experiences into changes in the brain.”

It’s crazy to think that we still don’t quite understand the mechanism behind one of the most common medical interventions — general anaesthetic.

But researchers in Australia just got a step closer by discovering that one of the most commonly used anaesthetic drugs doesn’t just put us to sleep; it also disrupts communication between brain cells.

The team investigated the drug propofol, a super-popular option for surgeries worldwide. A potent sedative, the drug is thought to put us to sleep through its effect on the GABA neurotransmitter system, the main regulator of our sleep-and-wake cycles in the brain.