Duke University researchers have equipped rats with implanted sensors that enable them to see and respond to infrared light, which is normally invisible to rodent (and human) eyes. Rats in the future could be given full-fledged infrared vision, and even humans can be given the ability to see in any region of the electromagnetic spectrum, or even magnetic fields in the future. Expanding sensory abilities could also enable a new type of feedback to improve the speed and accuracy of exoskeletons, said Professor Miguel Nicolelis, who led the research team.

This is the very first time when a brain-machine interface has augmented a sense in adult animals, said Duke University neurobiologist Miguel Nicolelis. In his famous BCI lab, Nicolelis and his colleagues have given rats the ability to “touch” infrared light, by fitting them with an infrared detector wired to microscopic electrodes implanted in the brain, in the part where it processes tactile information.

Another sensational finding of the experiment is that the implants have not “hijacked” the normal functions of the brain. This discovery suggests, for example, that a person whose visual cortex was damaged could regain sight through a neuroprosthesis implanted in another cortical region, said Nicolelis.

“We could create devices sensitive to any physical energy,” he said. “It could be magnetic fields, radio waves, or ultrasound. We chose infrared initially because it didn’t interfere with our electrophysiological recordings.”

“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, first author of the study. “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.”

Nicolelis is best known for his work in brain-computer interfaces and making mind-controlled prosthetics. His famous plan is to develop devices that would allow a quadriplegic child to walk onto a soccer field and make the first kick of the 2014 FIFA World Cup.

Details of the experiment

The researchers used a test chamber that contained three light sources that could be switched on randomly. Using visible LED lights, they first taught each rat to choose the active light source by poking its nose into an attached port to receive a reward of a sip of water. After training the rats, the researchers implanted in their brains an array of stimulating microelectrodes, each roughly a tenth the diameter of a human hair.

Attached to the electrodes was an infrared detector affixed to the animals’ foreheads. The system was programmed so that orientation toward an infrared light would trigger an electrical signal to the brain. The signal pulses increased in frequency with the intensity and proximity of the light.

The researchers returned the animals to the test chamber, gradually replacing the visible lights with infrared lights. At first in infrared trials, when a light was switched on the animals would tend to poke randomly at the reward ports and scratch at their faces, said Nicolelis. This indicated that they were initially interpreting the brain signals as touch. However, over about a month, the animals learned to associate the brain signal with the infrared source. They began to actively “forage” for the signal, sweeping their heads back and forth to guide themselves to the active light source. Ultimately, they achieved a near-perfect score in tracking and identifying the correct location of the infrared light source.

To ensure that the animals were really using the infrared detector and not their eyes to sense the infrared light, the researchers conducted trials in which the light switched on, but the detector sent no signal to the brain. In these trials, the rats did not react to the infrared light.

A key finding, said Nicolelis, was that enlisting the touch cortex for light detection did not reduce its ability to process touch signals. “When we recorded signals from the touch cortex of these animals, we found that although the cells had begun responding to infrared light, they continued to respond to whisker touch. It was almost like the cortex was dividing itself evenly so that the neurons could process both types of information.

Expanding sensory abilities could enable a new type of feedback loop to improve the speed and accuracy of exoskeletons such as those being developed by the Walk Again Project, said Nicolelis. For example, while researchers are now seeking to use tactile feedback to allow patients to feel the movements produced by such “robotic vests,” the feedback could also be in the form of a radio signal or infrared light that would give the person information on the exoskeleton limb’s position and encounter with objects.

Nicolelis and colleagues Eric Thomson and Rafael Carra published their work in the journal Nature Communications on Feb. 12. 2013.

Original press release: eurekalert.org