X-Ray Vision For Lab Rats
February 13, 2013

Brain-Machine Interface Allows Rat To ‘Touch’ Infrared Light

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Alan McStravick for redOrbit.com - Your Universe Online

The mammalian retina is a masterful example of genetic engineering. Each moment our eyes are open, we take in mountains and mountains of data that has to be pored over, interpreted and processed by a specific cortical region within our brains. Despite their seemingly endless capabilities, even our retinas have their limits. That is, until today, with the release of a new study by researchers led by Duke University neurobiologist Miguel Nicolelis. In their study, the team was able to give laboratory rats the ability to “touch” infrared light. Infrared light is typically invisible to mammalian retinas.

A professor of neurobiology, biomedical engineering, and psychology and neuroscience, Nicolelis is also the co-director of the Center for Neuroengineering. Assisting him with his study were Eric Thomson and Rafael Carra. Thomson is a post-doctoral research associate. Carra, visiting from the University of Sao Paulo in Brazil, is studying medicine in his home country. Grant support for the study was provided by the National Institutes of Health.

The rats were able to detect the infrared light after the team fitted them with an infrared detector that was wired to microscopic electrodes implanted in the part of the mammalian brain that processes tactile information. It was the connection to this region of the brain responsible for the sense of touch that, at first, made the initial interaction with the infrared beam feel as though it was touching the rat subjects.

Another first celebrated by this study demonstrated how, for the first time, a sensory input could be implanted into a cortical region specialized for reception of information involving another of our senses, altogether without actually “hijacking” the region for the newly chosen function. According to Nicolelis, the suggestion made by this discovery is that if an individual´s visual cortex were damaged, negating their ability to see, it might now be possible to aid in their regaining the sense of sight by implanting a neuroprosthesis in another cortical region.

In Search of Infrared Vision

The initial experiments with the laboratory rats were conducted to determine whether or not they could even detect infrared light. Team leader Nicolelis has claimed, however, he sees no reason why, in the future, animals couldn´t be given full-fledged infrared vision. In fact, with the use of a neuroprosthesis, there is no reason why animals and humans couldn´t be given the ability to see in any region of the electromagnetic spectrum.

Nicolelis even believes we might one day be able to see magnetic fields.

“We could create devices sensitive to any physical energy. It could be magnetic fields, radio waves or ultrasound. We chose infrared initially because it didn´t interfere with our electrophysiological recordings,” he said.

"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 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."

In addition to residing in an unseen area of the spectrum for mammals, infrared light does not produce any detectable heat for the laboratory subjects. Part of the method for the testing involved the use of a test chamber containing three light sources, each of which were enabled to be switched on randomly. Through the use of visible LED lights, the research team 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.

Once the initial training had been completed, the team undertook the task of implanting in the rat brains an array of stimulating microelectrodes. Each microelectrode was roughly one tenth the diameter of a single human hair. The area of the brain selected for implantation of the microelectrodes was the cortical region responsible for processing touch information from the rats´ facial whiskers.

The next part of the experiment involved affixing an infrared detector to the animals´ foreheads. Once the detector noted the presence of an infrared light signal, an electrical signal was sent into the brain. The generated signal pulses would increase in frequency with the intensity and proximity of the light.

With their subjects fully outfitted with their sixth sense accoutrement, the team reintroduced the rats back into the initial test chamber. The intent was to slowly replace the visible LED light with infrared light. At the switchover from LED to infrared, the rats typically would poke around randomly at the reward points. What was of interest to Nicolelis was how the rats would scratch at their faces. He commented how this was an indication they were initially interpreting the brain signals firing off as a result of the infrared light as affecting their touch sense.

It took at least a month for the rats to learn to associate the brain signal with the infrared source. However, once they learned, they began to actively “forage” for the signal. They did this by sweeping their heads back and forth hoping to guide themselves to the active light source. It wasn´t long until the rat subjects began racking up near-perfect scores in tracking and identifying the correct location of the infrared light source.

The researchers wanted to make certain the rats were actually using their infrared detectors and not their eyes to sense the infrared light. This was achieved when the team would present the infrared light while inhibiting the signaling to the cortical region. When no signal was sent to the brain, the rats failed to have any reaction to the infrared light.

A Paradigm Shift in Neurobiology

As mentioned above, the team wanted to try to use a non-native cortex to aid in providing a new sense to the animals. But equally important to creating the new sense was to ensure the native sense for the cortex, in this case the sense of touch, was in no way inhibited.

“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,” Nicolelis pointed out.

This even division of brain plasticity stands as a stark opposite to the “optogenetic” approach to brain stimulation. Optogenetics holds a particular neuronal cell type which should be stimulated to generate a desired neurological function. With this new study, Nicolelis recognizes how their findings might yield a paradigm shift in neurobiology. He contends their experiments demonstrate how broad electrical stimulation, which recruits many distinct cell types, can lead a specialized cortical region to adapt to a new source of sensory input.

Looking Towards the Future

Aside from the giddiness this author is feeling at the prospect of X-ray vision in my lifetime, this study has current, real-world applications. The team, in addition to helping rats to see infrared light, also announced they were able to record brain signals from almost 2,000 brain cells simultaneously. According to Nicolelis, the sheer amount of recording was unprecedented.

The researchers have their sights set on increasing the number of recorded individual brain cells and their electrical activity up to 10,000 cortical neurons. When they are able to achieve this feat, a level of precision will be achieved in the control of motor neuroprostheses. Motor neuroprostheses, like those being developed by the Walk Again Project, are important in helping to restore motor control to paralyzed people.

The Walk Again Project has recently received a $20 million grant from FINEP, a Brazilian research funding agency to allow the development of the first brain-controlled whole body exoskeleton aimed at restoring mobility in severely paralyzed patients. A first demonstration of this technology is expected to happen in the opening game of the 2014 Soccer World Cup in Brazil.

Nicolelis discussed how the expansion of sensory ability could also aid in enabling a new type of feedback loop to improve the overall speed and accuracy of such exoskeletons. As an example, he points out how researchers now seek to use tactile feedback to allow patients to feel the movements produced by such “robotic vests”, the feedback could also be presented to the user in the form of a radio signal or infrared light. This difference would give the user information on the exoskeleton limb´s position and its individual encounters with objects.

Once again, rats are the preferred model for researchers in helping to lead us to a fantastic future of special senses of sight and helping the paralyzed to walk upright. If you are interested in the work Nicolelis and his team will continue to undertake, stop by the Nicolelis laboratory web site.

The study findings were published this week in the online journal Nature Communications.