Peripheral neurostimulation for encoding artificial somatosensations

Abstract

The direct neural stimulation of peripheral or central nervous systems has been shown as an effective tool to treat neurological conditions. The electrical activation of the nervous sensory pathway can be adopted to restore the artificial sense of touch and proprioception in people suffering from sensory‐motor disorders. The modulation of the neural stimulation parameters has a direct effect on the electrically induced sensations, both when targeting the somatosensory cortex and the peripheral somatic nerves. The properties of the artificial sensations perceived, as their location, quality and intensity are strongly dependent on the direct modulation of pulse width, amplitude and frequency of the neural stimulation. Different sensory encoding schemes have been tested in patients showing distinct effects and outcomes according to their impact on the neural activation. Here, I reported the most adopted neural stimulation strategies to artificially encode somatosensation into the peripheral nervous system. The real‐time implementation of these strategies in bionic devices is crucial to exploit the artificial sensory feedback in prosthetics. Thus, neural stimulation becomes a tool to directly communicate with the human nervous system. Given the importance of adding artificial sensory information to neuroprosthetic devices to improve their control and functionality, the choice of an optimal neural stimulation paradigm could increase the impact of prosthetic devices on the quality of life of people with sensorimotor disabilities.

Neuromorphic hardware for somatosensory neuroprostheses

“…Different types of neural interfaces have been adopted to record the neural activity from the brain 33 – 35 or nerves 36 – 38 and, more recently, to also deliver electrical stimulation to peripheral nerves 4 , 11 , 39 – 44 (see Box 3 for more details), spinal cord 45 , 46 , or cortex 47 – 49 to restore sensory-motor functions. The use of electrical stimulation patterns allows for a valuable and reliable tool to directly communicate with the human nervous system enabling it to encode artificial sensory information 50 . Its effectiveness and functionality for sensory feedback restoration are strongly dependent on the characteristics of the adopted neural interface (i.e., implantable electrode).…”

“…Moreover, each electrode activates tens or hundreds of axons and elicits highly unnatural synchronous activation of these afferents. Until much denser and more selective neural interfaces become available, attempts to mimic natural nerve responses will have to settle for mimicking aggregate neural responses 14 , 50 , 65 . In the natural sensory processing condition, the spatiotemporal dynamics of this aggregate population response in the sensory cortex seem to mirror those of the population response in the nerves 66 , making the assumptions more generalizable for the entire somatosensory neuroaxis.…”

“…Currently, in the neuroprosthetic field, the scheme of neural stimulation is mostly not defined by the nerve’s natural coding or neuromorphic models (Fig. 2A ) 50 . Indeed, after defining the pulse waveform of the stimulation train, the modulation occurred only on a single parameter and mostly on individual channels of the neural interface.…”

Biohybrid Robotic Hand to Investigate Tactile Encoding and Sensorimotor Integration

“…However, one major challenge for conveying tactile sensations through neural interfaces is the mapping from the tactile sensor to the electrical stimulation parameters. Prosthetic fingertip sensations have been encoded in numerous different ways, which impacts not only their qualitative perception but also the closed-loop grasp control performance [30]. Several prior works have investigated frequency [31] or amplitude-modulated spike trains [32] to convey graded biomimetic sensations of touch to amputees outfit with neuroprosthetic limbs interfaced with peripheral nerves [33].…”

Wearable High Voltage Compliant Current Stimulator for Restoring Sensory Feedback

“…Several solutions have been proposed in literature to restore sensory feedback in amputees [11][12][13][14][15][16][17][18][19][20][21].…”