Turns out what monkeys see can affect what they do—or at least what they feel.
A new study conducted by neuroscientists at Duke’s Nicolelis Lab shows that the part of the brain responsible for the sensation of touch may react to visual stimuli alone. In the study, while monkeys were being touched on the arm, they viewed a video simulation of that same action. When the researchers stopped the physical stimulation, the areas of the monkeys’ brains responsible for tactile sensation still continued to respond to the virtual simulation.
These results support a previous hypothesis from the Nicolelis Lab, which suggests that functions of the cortex are not as rigidly segregated as once believed.
“After our results, neuroscience textbooks will definitely have to be updated,” Mikhail Lebedev, senior research scientist at the lab, wrote in an email Friday. “They teach that the motor cortex is for moving limbs, the somatosensory cortex is for feeling touch and the visual cortex is for seeing. Our results show a much more distributed representation of information in the brain.”
Untrained monkeys were implanted with up to 384 electrodes to analyze how stimulus was encoded by the monkey brain.
The monkeys were then shown a virtual simulation of their arm being touched, while simultaneously having their own arm touched. After a few minutes of synchronized stimulation, the physical component was removed.
The areas of the monkeys’ brains responsible for tactile sensations, however, continued to respond to the virtual simulation, indicating that they felt physical sensation simply through visual association.
The monkeys’ neuronal responses to the virtual stimulation came later than the responses to the physical stimulation. This suggests that the sensation was mediated by a longer pathway involving the visual system.
Instead of previously-imagined single neuronal pathways, seemingly unrelated cortices apparently use a highly-dynamic, cross-functional process to form more of a continuously interacting grid or network. They also appear to cooperate quite closely in shaping the body schema, or the brain’s internal representation of the body.
Researchers in the Nicolelis Lab are already using these concepts to develop neuroprosthetics for amputees and individuals with paralysis, or even in treating phantom limb pain. By becoming fully integrated into the brain’s body schema, artificial appendages could return motor function and tactile sensation to victims of paralysis or lost limbs.
The results imply that through brain-machine interfaces, such neuroprostheses could eventually be accepted by the brain as a natural extension of the body, said Dr. Miguel Nicolelis, professor of neurobiology, biomedical engineering and psychology and neuroscience.
“If we start using a tool, it is essentially assimilated into the brain as an extension of your body schema,” Nicolelis said.
Thus, like tools, cortically-driven limb prostheses could also be fully incorporated into the brain’s motor and sensory circuitry.
Although thought-controlled, touch-sensitive robotic limbs may seem like science fiction, they may not be so far off. In fact, Nicolelis and his associates are already working on a functioning prototype of the technology. Through a partnership with the Walk Again Project, they plan to create a full-body exoskeleton, powered by a brain-machine interface, capable of restoring a paralyzed individual’s ability to walk.
Unprecedented in its scale, the neuroprosthesis is planned to debut during the opening ceremony of the 2014 FIFA World Cup in Brazil. It will likely use electrical stimulation of sensory areas of the brain, called the neural stimulation approach, to produce sensation in the user, said Joseph O’Doherty, postdoctoral scholar at the University of California, San Francisco.
“These are just the general principles,” O’Doherty wrote in an email Sunday. “You will have to wait until the World Cup to see how they are specifically implemented.”