Of all the available wavelengths of light in the electromagnetic spectrum, most animals on Earth can only perceive what we call visible light – so called because it’s also what’s visible to the human eye.
But now, for the first time, rats have been augmented to ‘see’ infrared light, joining the optically enlightened ranks of some snakes and bats, thanks to researchers implanting sensors into their brains.
In a new study announced at the annual meeting of the Society for Neuroscience in the US, researchers from Duke University described how they were able to augment rat vision via inserting electrodes into the animals’ visual cortex.
One end of the electrodes, outside the rat’s head, picks up infrared light, and it sends this information down into the visual cortex – the part of the animal’s brain that processes visual information.
Two years ago, the same researchers had success with a similar technique, using a single electrode plugged into the animals’ somatosensory cortex, which processes the feeling of touch.
In that experiment, the animals detected infrared light, but not as a visual signal. As the electrode was inserted into their somatosensory cortex, they instead ‘touched’ infrared light – or rather, perceived the light via their sensation of touch, neurologically speaking. The researchers observed the rats grooming and rubbing their whiskers in response to the light, as if they could feel a physical presence.
This time the team went further, using four separate electrodes on the outside of the rats’ heads to detect infrared light coming in from 360 degrees. Before attempting to plug the electrodes into the visual cortex, they reran their original experiment, but with four times as much infrared input delivered to the animals’ somasensory cortex.
Interestingly, the extra inputs saw the animals perform significantly better in a reward-based task – learning to repeat the task in four days, compared with the 40 days it took them to learn with the single electrode.
“Frankly, this was a surprise,” one of the researchers, Eric Thomson, told Hanae Armitage at Science. “I thought it would be really confusing for [the rats] to have so much stimulation all over their brain, rather than [at] one location.”
The researchers redirected the same infrared signals directly to the animals’ visual cortex, and again their performance improved – this time learning the task in just one day. The researchers speculate that the animals’ accelerated adaptation may be related to the fact that infrared light is not too distant from visible light on the electromagnetic spectrum – an area of research other scientists have also been exploring.
In any case, the swift acceptance of the neural implants to augment animal senses gives hope to the researchers that treatments for humans might one day be able to give new senses to people – or perhaps restore senses to those who have lost them, such as giving vision back to those who have become blind.
“I’m still pretty amazed,” said Thomson. “Yes, the brain is always hungry for new sources of information, but the fact that it actually absorbed this new, completely foreign type so quickly is auspicious for the field of neuroprosthetics. And that’s why I’m excited.”
The research was presented at Neuroscience 2015.