Have It Your Way

Today’s prosthetics are just a fledgling step toward replicating the amazing functionality of human limbs. The ultimate goal is to integrate them with the nervous system of the user such that their thoughts can control the limbs, and sensations can be felt through them. This is a loft goal and it may still be many years before it is fully achieved. However, significant progress has been made in recent years.

A number of research efforts have focused on attempting to transmit sensations from the artificial limb to the user via sensors and brain-computer interfaces. There has been some meaningful progress in this area, yet the sensations produced are still very coarse and lacking realism. Many such systems produce simplistic buzzing or tingling feelings that do not really correspond with anything in the real world.

A team led by researchers at the University of Pittsburgh is working on a new solution to this problem that, while still imperfect, provides users with a far more realistic experience of touch sensations. Their technology is like other existing approaches in many ways — sensations are produced by stimulating a region of the brain responsible for processing sensory information from the body, for instance. But there is also a significant difference. The team made it possible for each user to fine-tune the stimulation they receive so that it more closely matches what they expect to feel. This tweak makes for a more realistic experience.

Using a tablet-based interface, study participants — all of whom had lost sensation in their hands due to spinal cord injury — interacted with virtual objects like a cat, key, apple, toast, and towel. As they "touched" these items on-screen, implanted electrodes delivered electrical stimulation directly to their brain’s somatosensory cortex.

Unlike prior approaches that offered a fixed stimulation pattern, this system allowed participants to control key aspects of the electrical signals — such as amplitude, frequency, and timing — without knowing which parameter they were adjusting. This blinded control method helped participants avoid bias and explore a wide range of sensations more efficiently. The goal was to replicate the real-world feeling of interacting with the virtual objects.

The results were promising, but not perfect. When the visual cues were removed, participants were still able to correctly identify one of five objects 35% of the time. Not great, but still significantly better than random guessing.

Interestingly, when errors did occur, they often reflected logical confusion. For instance, users were more likely to mistake the cat for the towel — both soft — than for the key. This suggests that users were tuning their stimulation settings in ways that corresponded with real-world tactile characteristics.

While far from perfect, the findings show that participants can use brain stimulation to create and distinguish realistic, personalized sensations. This advancement could one day lead to prosthetic limbs that feel far more natural to use, enhancing both functionality and quality of life for people with severe physical impairments.