Providing sense of touch via intracortical microstimulation of somatosensory cortex from a prosthetic limb
Research on brain computer interfaces has shown amazing progress over the past decade, with non-human primate studies showing that it is possible for monkeys to even learn guide an artificial arm based on neural signals recorded from the motor cortical areas. As such this line of research holds great promise for patients who have lost a limb or are suffering from paralysis due to spinal cord injury. One critical aspect that has been lacking in this exciting area of research has been the question of how somatosensory feedback could be provided from the prosthetic arm to the brain. This is important given that somatosensory feedback is a prerequisite for dexterous manipulation of objects and given that sense of touch is important for the embodied sensation (i.e., that limb feels part of oneself) as well as for emotional-social communication.
In their recent study, Tabot et al. (2013) compared the ability of monkeys to carry out somatosensory discrimination tasks based on endogenous vs. artificial somatosensory feedback inputs provided through native vs. prosthetic finger. Somatosensory stimulation was experimentally varied to find a set of parameters that could be used to guide manipulation of objects by the monkeys. The results suggest that 1) intracortical microstimulation of somatosensory cortex elicits spatially localized percepts consistently with the somatotopic organization of somatosensory cortex, 2) magnitude of the percept seems to depend on the magnitude of the microstimulation, and 3) phasic stimulation can be utilized to convey information about making of initial contact with an object. Based on these findings, the authors envision how microstimulation of the somatosensory cortex from a prosthetic limb could be used to provide sense of touch to human patients with an artificial limb.
Reference: Tabot GA, Dammann JF, Beg JA, Tenore FV, Boback JL, Vogelstein J, Bensmaia SJ. Restoring the sense of touch with a prosthetic hand through a brain interface. Proc Natl Acad Sci USA (2013) e-publication ahead of print. http://dx.doi.org/10.1073/pnas.1221113110