The results could provide an insight into learning and memory in humans.

The researchers were interested in an area of the brain called the perirhinal cortex, known to be involved in recognition memory. They inserted optical fibres into this region in the brains of participating rats, allowing them to stimulate specific neurons to fire at the whim of a scientist at a computer.

"In a sense we were trying to 'write in' novelty and 'write in' familiarity," explained Burwell.

The researchers presented rats with both new and old images, knowing that (like humans) rats spend more time looking at unfamiliar objects than familiar ones.

In normal conditions, the rats did indeed ignore images they’d seen before, and inspect the images they hadn’t. But the researchers found that stimulating neurons in the perirhinal cortex to alter the rate of firing could change this behaviour drastically.

At a stimulating frequency of 11Hz, rats became indifferent to images they had never seen before, despite their novelty. And at 30Hz, familiar images suddenly elicited new wonder. In other words, the rate of neurons firing in this brain region determined the rats’ perception of familiarity.

Given the multiple knock-on effects of familiarity and novelty on behaviour, the researchers now plan to use the same system to study how recognition influences decision-making.

Chances are, though, the rats will have seen it coming.

by Catherine E. Offord