It might sound like a very odd comic book, but it’s true: Scientists have given experimental rats the ability to “touch” infrared light. The researchers describe the experiment in a paper debuting on Monday in the journal Nature Communications.
“Part of the brain that was thought to be devoted to touch forever can actually be transformed,” senior author and Duke University neurobiologist Miguel Nicolelis said in a phone interview. “You can impose a new sensory modality on top of a representation that already exists in the brain.”
The discovery could lead to devices that could restore eyesight to the blind, or give humans the ability to add new senses -- ever wanted to taste radio waves, or hear the song of X-rays? It might not be too far off.
Nicolelis and his team outfitted rats with brain-implanted electrodes attached to an infrared detector. The electrodes were put in the area of the rats’ brains that processes the tactile signals received by their whiskers. (The researchers picked infrared – a form of light normally invisible to mammals -- because it wouldn’t interfere with the recording of the rats’ brain signals).
The scientists then trained the animals to poke at light sources – first in the visible spectrum, then infrared – inside little ports with their noses to receive water. At first, the animals would scratch at their faces when the infrared signal was switched on, or poke randomly at the ports.
But the rodents quickly caught on to their newfound sense for infrared, eventually learning to swing their heads around to “forage” for the infrared signal.
What the rats were sensing is unlike the normal kind of touch or sight that is usually experienced. It's hard to put into words. The sense the rats felt “probably evolved from first thinking there is a strange stimulation delivered to the face [from] some sort of perception of light that is out there,” Nicolelis said.
Nicolelis thinks the rodents may have been experiencing something like synesthesia – the neurological condition in people where sensory pathways get crossed. The condition manifests in a variety of ways; synesthetes may associate colors with certain letters and numbers, or find that sounds can provoke visions of various firework-like shapes.
The procedure the rats underwent is still pretty invasive, so it’s not easy to replicate the experiment into human subjects at present. But in the future there may be ways for researchers to piggyback new features onto sensory pathways without too much brain surgery. Doctors could reroute sensory pathways to restore vision to the blind, using microchip implants in the visual cortex.
Some people with perfectly normal eyesight may even want to add other options to their brains. Sensing infrared, as the rats did, would surely be an interesting experience – imagine being able to “see” the signal traveling from the remote control to your TV, or “feel” the data traveling through a fiber-optic cable.
"This could potentially augment our regular senses,” Nicolelis said.
SOURCE: Thomson et al. “Perceiving invisible light through a somatosensory cortical prosthesis.” Nature Communications published online 12 February 2013.