Los Angeles, April 11: For the first time, scientists have induced natural sensations in the arm of a paralysed man by stimulating a certain region of the brain with a tiny array of electrodes. The patient in the US has a high-level spinal cord lesion and, besides not being able to move his limbs, also cannot feel them. The work could one day allow paralysed people using prosthetic limbs to feel physical feedback from sensors placed on these devices.

The somatosensory cortex is a strip of brain that governs bodily sensations, both proprioceptive sensations (sensations of movement or the body's position in space) and cutaneous sensations (those of pressure, vibration, touch, and the like). Previously, neural implants targeting similar brain areas predominantly produced sensations such as tingling or buzzing in the hand.

The implants developed by California Institute of Technology in the US is able to produce much more natural sensation via intracortical stimulation, akin to sensations experienced by the patient prior to his injury. The patient had become paralysed from the shoulders down three years ago after a spinal cord injury. Two arrays of tiny electrodes were surgically inserted into his somatosensory cortex.

Using the arrays, the researchers stimulated neurons in the region with very small pulses of electricity. The participant reported feeling different natural sensations - such as squeezing, tapping, a sense of upward motion, and several others - that would vary in type, intensity, and location depending on the frequency, amplitude, and location of stimulation from the arrays. It is the first time such natural sensations have been induced by intracortical neural stimulation.

"It was quite interesting. It was a lot of pinching, squeezing, movements, things like that. Hopefully it helps somebody in the future," the patient said. Though different types of stimulation did indeed induce varying sensations, the neural codes governing specific physical sensations are still unclear. In future work, researchers hope to determine the precise ways to place the electrodes and stimulate somatosensory brain areas in order to induce specific feelings and create a kind of dictionary of stimulations and their corresponding sensations.