Scientists have given rats a sixth sense: the ability to see infrared light.

A device implanted in the rats' brains allowed the rats to "see" infrared light. The infrared detector was wired to electrodes implanted to the region of the rat brain that processes tactile information. The microscopic electrodes were about 1/10 the diameter of a human hair.

The research, conducted at Duke University, represents the first time a brain-machine interface has given an adult animal an extra sense. It also shows that we can assign a sense to a region of the brain normally reserved for processing a different kind of information.

"We could create devices sensitive to any physical energy," Professor Miguel Nicolelis told the BBC. Nicolelis is the lead author of the study, conducted at the Duke Medical Center in Durham, North Carolina. "It could be magnetic fields, radio waves or ultrasound. We chose infrared initially because it didn't interfere with our electrophysiological recordings."

The rats were tested in a chamber with three independent light sources. They were trained to identify which source was emitting light by poking their noses into a port, which rewarded them with water. The researchers then implanted the electrodes in the rats' brains and returned the animals to the test chamber, this time using infrared light, normally invisible to rat vision.

At first, the rats interpreted the infrared energy as a tactile touch, scratching at their faces as if an object was rubbing against their whiskers. But soon the rats learned to interpret the sensation as coming from the infrared source.

The researchers also found that using the touch cortex to detect infrared light did not affect the rat's ability to process the feeling of touch. This could have big implications for patients suffering from brain damage, as a lost sense could potentially be restored by sharing processing power from a different sensory region of the brain.

"The philosophy of the field of brain-machine interfaces has until now been to attempt to restore a motor function lost to lesion or damage of the central nervous system," said Eric Thomson Nicolelis' colleague. But this research may lead to more than just restoring lost senses. "This is the first paper in which a neuroprosthetic device was used to augment function - literally enabling a normal animal to acquire a sixth sense."