Amputees discern familiar sensations across prosthetic hand

Even before he lost his right hand to an industrial accident 4 years ago, Igor Spetic had family open his medicine bottles. Cotton balls give him goose bumps.

Now, blindfolded during an experiment, he feels his arm hairs rise when a researcher brushes the back of his prosthetic hand with a cotton ball.

Spetic, of course, can’t feel the ball. But patterns of electric signals are sent by a computer into nerves in his arm and to his brain, which tells him different. “I knew immediately it was cotton,” he said.

That’s one of several types of sensation Spetic, of Madison, Ohio, can feel with the prosthetic system being developed by Case Western Reserve University and the Louis Stokes Cleveland Veterans Affairs Medical Center.

Spetic was excited just to “feel” again, and quickly received an unexpected benefit. The phantom pain he’d suffered, which he’s described as a vice crushing his closed fist, subsided almost completely. A second patient, who had less phantom pain after losing his right hand and much of his forearm in an accident, said his, too, is nearly gone.

Read more

New findings on how brain handles tactile sensations

The traditional understanding in neuroscience is that tactile sensations from the skin are only assembled to form a complete experience in the cerebral cortex, the most advanced part of the brain. However, this is challenged by new research findings from Lund University in Sweden that suggest both that other levels in the brain play a greater role than previously thought, and that a larger proportion of the brain’s different structures are involved in the perception of touch.

“It was 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.

“Our findings have given us a new key to understanding how the perception of touch in the skin is processed and communicated to the brain”, he said.

The Lund researchers have 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 findings of the Swedish-French research group have been published in the distinguished journal Neuron. The work is based on animal experiments and is first and foremost basic research, which aims to increase knowledge of the function of the brain. However, there are also possible areas of application.

“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 Henrik Jörntell.

The new findings could also have a bearing on psychiatric illness and brain diseases such as stroke and Parkinson’s disease. Detailed knowledge of how the brain and its various parts process information and create a picture of a tactile experience is important to understanding these conditions.

“If we know how a healthy brain operates, we can compare it with the situation in different diseases. Then perhaps we can help patients’ brains to function more normally”, said Henrik Jörntell.

Problem-solving governs how we process sensory stimuli

Various areas of the brain process our sensory experiences. How the areas of the cerebral cortex communicate with each other and process sensory information has long puzzled neuroscientists. Exploring the sense of touch in mice, brain researchers from the University of Zurich now demonstrate that the transmission of sensory information from one cortical area to connected areas depends on the specific task to solve and the goal-directed behavior. These findings can serve as a basis for an improved understanding of cognitive disorders.

In the mammalian brain, the cerebral cortex plays a crucial role in processing sensory inputs. The cortex can be subdivided into different areas, each handling distinct aspects of perception, decision-making or action. The somatosensory cortex, for instance, comprises the part of the cerebral cortex that primarily processes haptic sensations. The different areas of the cerebral cortex are interconnected and communicate with each other. A central, unanswered question of neuroscience is how exactly do these brain areas communicate to process sensory stimuli and produce appropriate behavior. A team of researchers headed by Professor Fritjof Helmchen at the University of Zurich’s Brain Research Institute now provides an answer: The processing of sensory information depends on what you want to achieve. The brain researchers observed that nerve cells in the sensory cortex that connect to distinct brain areas are activated differentially depending on the task to be solved.

Goal-directed processing of sensory information

In their publication in Nature, the researchers studied how mice use their facial whiskers to explore their environment, much like we do in the dark with our hands and fingers. One mouse group was trained to distinguish coarse and fine sandpapers using their whiskers in order to obtain a reward. Another group had to work out the angle, at which an object – a metal rod – was located relative to their snout. The neuroscientists measured the activity of neurons in the primary somatosensory cortex using a special microscopy technique. With simultaneous anatomical stainings they also identified which of these neurons sent their projections to the more remote secondary somatosensory area and the motor cortex, respectively.

The primary somatosensory neurons with projections to the secondary somatosensory cortex predominantly became active when the mice had to distinguish the surface texture of the sandpaper. Neurons with projections to the motor cortex, on the other hand, were more involved when mice needed to localize the metal rod. These different activity patterns were not evident when mice passively touched sandpaper or metal rods without having been set a task – in other words, when their actions were not motivated by a reward. Thus, the sensory stimuli alone were not sufficient to explain the different pattern of information transfer to the remote brain areas.

Impaired communication in the brain

According to Fritjof Helmchen, the activity in a cortical area can be transmitted to remote areas in a targeted fashion if we have to extract (‘filter’) specific information from the environment to solve a problem. In cognitive disorders such Alzheimer’s disease, Autism, and Schizophrenia, this communication between brain areas is often disrupted. “A better understanding of how these long-range, interconnected networks in the brain operate might help to develop therapies that re-establish this specific cortical communication,” says Helmchen. The aim would be to thereby improve the impaired cognitive abilities of patients.