Restoring the sense of touch with a prosthetic hand through a brain interface

Abstract

The authors note, "For the 'hybrid' location discrimination task, we report data obtained from 27 electrodes, 16 of which were in area 1; the 11 electrodes in area 3b were divided evenly across the two animals (6 and 5). We had previously tested all of the electrodes, including those in area 3b, in the detection and discrimination tasks (as shown in Fig. 3) and found them all to yield approximately equivalent performance (see Fig 3A). We noticed in the hybrid location discrimination task, however, that one of the animals performed much more poorly based on stimulation of area 3b than it did based on stimulation of area 1 (while the other animal performed better based on stimulation of area 1). Having no reason to question any of the arrays, we attributed this discrepancy to differences across animals and arrived at the conclusion, based on pooled data from both animals, that stimulation of the two areas yields equivalent performance in the 'hybrid location discrimination' task. The overall conclusion, then, was that stimulation of neurons in area 3b and 1 evokes percepts that are equally localized on the skin."Shortly after publication of the paper, we repeated detection experiments across the arrays and found that the animal could no longer detect stimulation through the array in area 3b that had yielded poor performance in the hybrid location discrimination task. It is therefore likely that this array had failed between the time we conducted the initial detection and discrimination experiments and the time we conducted the hybrid location discrimination task (which required 2-3 months of retraining). If this is the case, and we eliminate data from that bad array, then the median performance on hybrid trials is 83% (up from the 80% that was originally reported), which is still statistically poorer than that on the location-matched mechanical trials [median difference between performance on mechanical and hybrid trials was 3.3% rather than 5.6%, t (119) = 6.1, P < 0.001] (see the corrected Fig. 2). Thus, we probably underestimated overall performance on hybrid trials, and thus the degree to which artificial percepts are localized, in the original publication. Importantly, however, performance on hybrid trials based on stimulation of area 3b was significantly better than performance based on stimulation of area 1 [median Δp = 0.028 and 0.054 for areas 3b and 1, respectively; t test: t (76) = 2.8, P < 0.01]. Thus, based on the data obtained from only one animal, it seems as though stimulation of area 3b elicits more localized percepts than does stimulation of area 1, as might be expected given that neurons in area 3b tend to have smaller receptive fields than their counterparts in area 1 (1, 2)."As a result of this error, Fig. 2 and its legend appeared incorrectly. The corrected figure and its corresponding legend appear below. On both mechanical and hybrid trials, the relative locations of stimuli applied to widely spaced digits were more accurately discriminated than were the relative locations of stimuli applie...

Ownership of an artificial limb induced by electrical brain stimulation

“…Subdural electrode arrays have some advantages for long-term implantation over fine-wire intracortical electrodes, as they are less invasive and provide a more stable signal over time at the cost of poorer spatial resolution (28). The results of microstimulation studies in monkeys (29)(30)(31)(32)(33) and a recent study in one human participant (34) suggest that intracortical microstimulation of the SI cortex provides more natural sensations of touch localized to substantially smaller areas of the skin. However, we speculate that the crossmodal interaction effect discussed above could potentially be exploited to increase the diversity of somatosensory percepts induced by ECoG stimulations of the SI cortex.…”

Making sense: Determining the parameter space of electrical brain stimulation

“…Constant current pulses were delivered through electrode arrays placed over the functionally identified hand area of the somatosensory homunculus in areas 1 and 3b (Fig. 1), between which this group has demonstrated previously that detection thresholds with varying current amplitudes are similar (12). Pulse width and frequency and pulse train duration were varied parametrically here, revealing that thresholds for detection decrease as the magnitudes of these parameters increase.…”

Key considerations in designing a somatosensory neuroprosthesis

“…However, we might be able to leverage certain key principles of sensory representations in the development of our algorithms. For example, the systematic somatotopic organization of somatosensory cortex might be used to convey information about contact location, both in cortex (Tabot et al, 2013) and in the sensory nerves (Stewart, 2003). We might be able to reproduce the coarse dynamics of neuronal activation evoked during object manipulation by modulating the dynamics of stimulation (Saal and Bensmaia, 2015), in the hopes of evoking more natural percepts during grasping and restoring crucial cues about contact events .…”

“…For amputees, somatosensory restoration involves interfacing with the nerve using chronically implanted multi-electrode arrays (Clark et al, 2014;Dhillon and Horch, 2005;Raspopovic et al, 2014;Tan et al, 2014). For tetraplegic patients, somatosensory feedback is conveyed by directly stimulating the brain, somewhere along the neuraxis from the brain stem through the somatosensory cortex (Bensmaia and Miller, 2014;Cushing, 1909;Dadarlat et al, 2015;Davis et al, 1998;Fitzsimmons et al, 2007;Kim et al, 2015;O'Doherty et al, 2009;O'Doherty et al, 2011;O'Doherty et al, 2012;Penfield and Boldrey, 1937;Richardson et al, 2016;Romo et al, 1998;Tabot et al, 2013). Besides restoring touch, this approach was also shown to be effective in decreasing or eliminating phantom limb pain (Horch et al, 2011;Rossini et al, 2010;Tan et al, 2014).…”