Limb sensation can be lost via a number of conditions, and leads to a significant decrease in motor control. However, microstimulation of specific areas of the cerebral cortex has shown potential to restore cutaneous (skin) sensation.
The loss of limb sensation was previously a crippling condition with little to no hope for return to a normal life. However, advances in technology have allowed for functional, artificial limbs that are controlled via a neural interface. Though these prosthetics have some function, the majority of motor control requires somatosensory feedback (between the body and its surroundings) to be more effective.
In amputees using neurologically-controlled limbs, electrical stimulation of nerves via electrodes has shown to cause feelings of sensation that allow for better prosthetic control. However, in individuals with spinal cord injury, the peripheral nerves are no longer viable for electrical stimulation. In these patients, a proposed approach is the use of microelectrodes to stimulate the cerebral cortex. Microelectrode stimulation has formed sensations in the visual cortex, and a new study focused on stimulation of the somatosensory area of the brain.
The study, conducted by Flesher et al. and published in Science Translational Medicine, was performed on one patient lacking hand sensation due to spinal cord injury. Microelectrode arrays were surgically implanted in the somatosensory cortex, at areas corresponding to the index and little fingers. Testing began 1 week after surgery and was conducted 2 to 3 times a week for up to 4 hours a session. The patient underwent testing for 6 months.
After six months of testing, the procedure yielded promising results. The patient reported the return of natural feeling sensation with intracortical stimulation. The sensations were also precise in that stimulation of different areas led to sensation in different areas of the hand. Also, increased stimulation intensity led to increased sensation intensity, the sensations did not decrease over the six months and there were no negative effects.
The study is limited because it was only conducted on one participant, meaning its results cannot be generalized to other spinal cord injuries or other conditions. Nonetheless, the discovery of the specificity and variability of intracortical microstimulation is promising for the use of prosthetic limbs in cases of lost sensation. Further studies should focus on including more cases, utilizing more microelectrodes to cover a greater area of the hand and using different stimulus patterns to provide different feedback.
Written By: Wesley Tin, BMSc