Engineering Artificial Somatosensation Through Cortical Stimulation in Humans.

Brian Lee,Spencer Kellis,Michelle Armenta Salas,Richard A Andersen,Tatyana Dobreva,Charles Liu,David Brown,Daniel Kramer,Christian Klaes,Christi Heck

doi:10.3389/fnsys.2018.00024

Abstract

Sensory feedback is a critical aspect of motor control rehabilitation following paralysis or amputation. Current human studies have demonstrated the ability to deliver some of this sensory information via brain-machine interfaces, although further testing is needed to understand the stimulation parameters effect on sensation. Here, we report a systematic evaluation of somatosensory restoration in humans, using cortical stimulation with subdural mini-electrocorticography (mini-ECoG) grids. Nine epilepsy patients undergoing implantation of cortical electrodes for seizure localization were also implanted with a subdural 64-channel mini-ECoG grid over the hand area of the primary somatosensory cortex (S1). We mapped the somatotopic location and size of receptive fields evoked by stimulation of individual channels of the mini-ECoG grid. We determined the effects on perception by varying stimulus parameters of pulse width, current amplitude, and frequency. Finally, a target localization task was used to demonstrate the use of artificial sensation in a behavioral task. We found a replicable somatotopic representation of the hand on the mini-ECoG grid across most subjects during electrical stimulation. The stimulus-evoked sensations were usually of artificial quality, but in some cases were more natural and of a cutaneous or proprioceptive nature. Increases in pulse width, current strength and frequency generally produced similar quality sensations at the same somatotopic location, but with a perception of increased intensity. The subjects produced near perfect performance when using the evoked sensory information in target acquisition tasks. These findings indicate that electrical stimulation of somatosensory cortex through mini-ECoG grids has considerable potential for restoring useful sensation to patients with paralysis and amputation.

Highlights

The incidence of new cases of spinal cord injury in the United States is estimated to be 12,000 per year
We identified sensory receptive fields on the hand, palm and fingers during the initial grid mapping (Table 3)
Some electrode pairs induced sensations in single digits, and others had receptive fields that spanned across multiple neighboring digits

Summary

Introduction

The incidence of new cases of spinal cord injury in the United States is estimated to be 12,000 per year. A bidirectional BMI to operate a robotic hand could read out signals from touch sensors in the hand, use stimulation of primary somatosensory cortex (S1) to write this information directly into the brain (Figure 1). As cognitive-based motor neuroprosthetics have garnered attention (Klaes et al, 2014), and touch sensors are available in commercial robotic limbs (Wettels et al, 2008), integrating artificial sensation into a cognitive neural prosthesis has become a realizable possibility (Fagg et al, 2009; Marzullo et al, 2010; O’Doherty et al, 2012). The external prosthesis would become incorporated into the patient’s body schema, featuring both motor control and somatosensory feedback (Gallagher and Cole, 1995; Botvinick and Cohen, 1998; Tsakiris and Haggard, 2005; Arzy et al, 2006)

Methods

Results

Conclusion