Researchers at Caltech have induced a range of sensations in the arm of a paralyzed man. The breakthrough comes courtesy of electrodes implanted in the brain, which stimulated the neurons to produce different feelings depending on the type of electrical signals. The team says the research could eventually lead to advanced prosthetic limbs that allow users to feel realistic sensations through them.

Plenty of exciting research is being conducted to help paralyzed people regain control of and feeling in their limbs. The NeuroLife system has helped a quadriplegic man move his arms again using just his thoughts, allowing him to perform a number of actions. Electrical nerve stimulation, both with and without electrode implants, has helped several people voluntarily move their legs again, often for the first time in years.

In this new study, Caltech researchers implanted two tiny arrays of electrodes into the somatosensory cortex, the small region of the brain responsible for the body's sensations of movement or position, as well as cutaneous sensations such as touch, pressure and vibration.

The patient had lost the ability to register these sensations in his limbs after a spinal cord injury three years prior, but the team was able to induce them artificially by using the electrodes to stimulate neurons in the somatosensory cortex. The patient reported feeling like his arm was being squeezed, tapped, or moved upwards, and the researchers were able to induce different sensations and change the intensity and location of the feelings by adjusting the frequency, amplitude and location of the electrical signal through the electrodes.

Unfortunately for now, thanks to the overwhelming complexity of the human brain, the researchers haven't yet untangled exactly which parts of the somatosensory cortex correspond to which sensations. That's the next step of the study, and the team says that the eventual goal is to tie the stimulation system to prosthetic limbs to allow patients to feel specific types of touch through them as though they were their own – much like the case of Nathan Copeland a few years ago.

"Currently the only feedback that is available for neural prosthetics is visual, meaning that participants can watch the brain-controlled operation of robotic limbs to make corrections," says Richard Andersen, lead researcher on the study. "However, once an object is grasped, it is essential to also have somatosensory information to dextrously manipulate the object. Stimulation-induced somatosensory sensations have the potential added advantage of producing a sense of embodiment; for example, a participant may feel over time that the robotic limb is a part of their body."

The research was published in the journal eLife.

Source: Caltech