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A novel experiment that gives rats the ability to "feel" infrared light by hijacking their sense of touch may require scientists to re-evaluate their ideas about how the brain works, says the lead researcher behind the study.
Six rats were implanted with electrodes that connect their brains to infrared sensors they wore on the tops of their heads. The electrodes were inserted into each animal's somatosensory cortex – the part of a rat's brain that is responsible for sensing touch, particularly through the whiskers.
When the wired rats were placed in a situation where infrared lights were turned on and off around them, they first responded as though they were feeling an invisible touch to their whiskers. Within a few days, however, the rats' responses changed and they were able to identify and move toward sources of infrared light as though "seeing" them in the distance.
"They basically started behaving like they're projecting the sensation of touch into the outside world," says Miguel Nicolelis, a professor of neurobiology and bioengineering at Duke University in Durham, North Carolina, who led the experiment.
What is especially intriguing is that Dr. Nicolelis and his colleagues made no special effort to connect the infrared sensors to specific neurons apart from placing then in the general brain region associated with touch.
"We didn't have to go fishing for the right cells," says Dr. Nicolelis.
The results suggest that adult brains are for more plastic than expected and, aided by so-called neuro-prosthetic devices, can quickly develop new sensory modalities that operate on top of the conventional five senses.
Dr. Nicolelis says the work could lead to ways of helping human patients acquire a different kind of sight even when the visual cortex is damaged. Currently, damage to the brain's visual processing centre is considered an insurmountable barrier to regaining a sense of sight.
In the future, Dr. Nicolelis adds, people who suffer no impairments at all may opt to add to their sensory capabilities with implants that allow them to sense types of stimuli that are otherwise invisible.
"I tell my students that Superman must have a neuro-prosthesis for X-ray vision," says Dr. Nicolelis.
The study, published in the journal Nature Communications, is one of several illustrating the rapid advancements under way in brain-machine interfaces. The field is the focus of a session on Sunday at the annual meeting of the American Association for the Advancement of Science in Boston.
The work has also attracted the attention of bioethicists exploring how technologies that enhance the brain may one day change our concept of what it means to be human. Despite the futuristic nature of the technology, it not too soon to discuss its implications, says Martha Farah, director of the Center for Neuroscience and Society at the University of Pennsylvania in Philadelphia.
"Part of the point in having discussions at this stage, in anticipation of these technologies being available, is that we can perhaps decide how would we like our society to manage and guide their use," says Dr. Farah.
Ivan Semeniuk