September 2014 issue
September 30, 2014 | One of the greatest challenges confronting the neuroprosthetics field is the integration of meaningful sensory input into prosthetic limbs. Two new research findings—each challenging conventional thinking in somatosensory neuroscience—may assist neural engineers incorporating sensory feedback into prosthetic or paralyzed upper limbs.
Traditional understanding in neuroscience is that tactile sensations from the skin are only assembled to form a complete experience in the cerebral cortex. However, this was challenged by new research findings from Lund University in Sweden that suggest that other levels in the brain play a greater role than previously thought, and that a larger proportion of the brain’s structures are involved in the perception of touch.
“It was previously believed that a tactile sensation, such as touching a simple object, only activated a very small part of the cerebral cortex. However, our findings show that a much larger part is probably activated. The assembly of sensations actually starts in the brainstem,” said neuroscience researcher Henrik Jörntell at Lund University.
According to his colleague Fredrik Bengtsson, who also participated in the research, this is the first study to show how complex tactile sensations from the skin are coded at the cellular level in the brain.
The Lund researchers worked in collaboration with researchers in Paris to study how individual nerve cells receive information from the skin. They used a haptic interface, which created controlled sensations of rolling and slipping movements and of contact initiating and ceasing. Movements proved decisive for the perception of touch—something that was not previously technically possible to study.
The group’s findings were published in Neuron. The work is based on animal experiments. “Normal hand and arm prostheses do not give any feedback and therefore no sensation of being a “real” hand or arm. However, there are new, advanced prostheses with sensors that can supply information to the amputated arm. Our research could contribute to the further development of such sensors,” said Jörntell.
Meanwhile, a team of neuroscientists at the University of Chicago argued in the journal Trends in Neurosciences that different types of nerves and skin receptors work in concert to produce sensations of touch, Their assertion challenges a long-held principle in the field—that separate groups of nerves and receptors are responsible for distinct components of touch, like texture or shape. They hope to change the way somatosensory neuroscience is taught and how the science of touch is studied.
Sliman Bensmaia and Hannes Saal reviewed more than 100 research studies on the physiological basis of touch published over the past 57 years. They argue that evidence once thought to show that different groups of receptors and nerves, were responsible for conveying information about separate components of touch to the brain actually demonstrates that these afferents work together to produce the complex sensation.
“Any time you touch an object, all of these afferents are active together,” Bensmaia said. “They each convey information about all aspects of an object, whether it’s the shape, the texture, or its motion across the skin.”
