Bionics An artificial sense of touch for paraplegics

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Researchers at Chalmers University of Technology have developed a groundbreaking method to restore complex tactile sensations in the limbs of paraplegic individuals. The approach uses an external device attached to the wheelchair, which performs movements, with the tactile signals transmitted directly to the patient's brain via targeted stimulation.

The sense of touch is of fundamental importance for carrying out everyday tasks independently. In people living with spinal cord injuries, the signals from the hand to the brain are impaired. This often leads to paraplegia and an associated loss of tactile sensations in the affected parts of the body.

Over the years, medical research has pursued various approaches to restore a certain degree of independence to affected patients. One of the most promising areas is bionics, the augmentation of biological functions with robotic aids. In recent years, various concepts of bionic limbs have been developed that are controlled by brain signals. These are generally functional, but the lack of sensory feedback makes tasks such as lifting and manipulating objects difficult. Without a sense of touch, a bionic hand often feels more like a tool than an extension of the body. This makes direct handling of the objects to be manipulated more difficult.

A research team at Chalmers tekniska högskola (Chalmers University of Technology) in Gothenburg, Sweden, has focused on how this missing sense of touch can be simulated in so-called extracorporeal bionic limbs - robotic arms that are attached to a wheelchair or similar device close to the user. The aim is to create a seamless connection between the brain and the bionic limb, enabling both control and sensory feedback. In a study published in the current issue of the journal Science, the researchers describe that they have now succeeded in using a brain-controlled bionic limb to provide a paralyzed person with tactile sensations related to orientation, curvature, movement and 3D shapes.

Control and sensation via electrodes in the brain

In the study, which was conducted by the US Cortical Bionics Research Group, two participants were fitted with brain implants that target the sensory and motor regions of the arm and hand. Over several years, the researchers recorded the patterns of electrical activity in the brain. In this way, they worked out which regions were active with regard to movement and the sense of touch. Although the paralysis prevented these signals from reaching the limbs, the electrical activity of the brain remained intact.

The use of brain impulses to control robotic or bionic limbs has already been successfully tested in other existing case studies. What is new is the haptic feedback that is generated by stimulating the corresponding brain regions. The participants successfully completed a series of complex experiments that required rich tactile sensations. To achieve this, the researchers transmitted specific stimuli directly to the brain via the implants. "We found a way to write these 'tactile messages' via microstimulation using tiny electrodes in the brain, and we found a unique way to encode complex sensations," says Giacomo Valle, lead author of the study and assistant professor at Chalmers University of Technology. "This allowed for more vivid sensory feedback and experience when using a bionic hand." For example, as the study explains, participants were able to feel the edge of an object and even recognize the direction of movement along their fingertips.

Using the brain-computer interface (BCI), the researchers decoded the participants' brain activity to control a bionic arm. When the arm's sensors detected contact with an object, signals were sent back to the brain, creating the sensation of touch as if the object were being held in a biological hand. This bidirectional communication allowed participants to perform complex tasks with greater accuracy, such as picking up an object and moving it to another location.

The study is a decisive first step on the way to enabling patients with spinal cord injuries to regain complex touch sensations. However, as the researchers admit, the approach is still in its infancy. Further progress and improvements are needed in both sensor and robot technology, e.g. the development of skin prostheses that can capture a wider range of tactile sensations. The implantable technology used for brain stimulation also needs to be further developed in order to expand the variety and nuance of sensations it can convey. (sg)