Mapping of primary somatosensory cortex of the hand area using a high-density electrocorticography grid for closed-loop brain computer interface

Abstract

Objective. The ideal modality for generating sensation in sensorimotor brain computer interfaces (BCI) has not been determined. Here we report the feasibility of using a high-density ‘mini’-electrocorticography (mECoG) grid in a somatosensory BCI system. Approach. Thirteen subjects with intractable epilepsy underwent standard clinical implantation of subdural electrodes for the purpose of seizure localization. An additional high-density mECoG grid was placed (Adtech, 8 by 8, 1.2 mm exposed, 3 mm center-to-center spacing) over the hand area of primary somatosensory cortex. Following implantation, cortical mapping was performed with stimulation parameters of frequency: 50 Hz, pulse-width: 250 µs, pulse duration: 4 s, polarity: alternating, and current that ranged from 0.5 mA to 12 mA at the discretion of the epileptologist. Location of the evoked sensory percepts was recorded along with a description of the sensation. The hand was partitioned into 48 distinct boxes. A box was included if sensation was felt anywhere within the box. Main results. The percentage of the hand covered was 63.9% (± 34.4%) (mean ± s.d.). Mean redundancy, measured as electrode pairs stimulating the same box, was 1.9 (± 2.2) electrodes per box; and mean resolution, measured as boxes included per electrode pair stimulation, was 11.4 (± 13.7) boxes with 8.1 (± 10.7) boxes in the digits and 3.4 (± 6.0) boxes in the palm. Functional utility of the system was assessed by quantifying usable percepts. Under the strictest classification, ‘dermatomally exclusive’ percepts, the mean was 2.8 usable percepts per grid. Allowing ‘perceptually unique’ percepts at the same anatomical location, the mean was 5.5 usable percepts per grid. Significance. Compared to the small area of coverage and redundancy of a microelectrode system, or the poor resolution of a standard ECoG grid, a mECoG is likely the best modality for a somatosensory BCI system with good coverage of the hand and minimal redundancy.

Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration

“…Such high degree of anatomical overlap among the evoked percepts restricts the amount of sensory information that can be conveyed. Meanwhile, with their the larger size and inter-contact spacing, HD-ECoG electrodes elicit more diffuse sensory percepts (14, 16, 53). Additionally, with the capability to record or modulate the neural activity of neurons that lie within 1-2 mm below the cortical surface (54), these electrodes provide access to only the gyral surfaces of the cortex.…”

“…Recently, tactile percepts in the hand have been evoked in humans through intracortical microstimulation using microelectrode arrays (11)(12)(13) or cortical surface stimulation using electrocorticography (ECoG) grids (14)(15)(16) in the primary somatosensory cortex (S1). Although such artificial sensory feedback help improve the user performance with a BCI system (17), focal percepts in fingertips that would be critical for dexterous manipulations have been difficult to achieve.…”

Novel intraoperative online functional mapping of somatosensory finger representations for targeted stimulating electrode placement

“…3,4 However, eliciting positive reports of sensory percepts instead of negative (numbness) reports or inactivating motor functions transiently 5 may be difficult, 38 and prior studies have demonstrated low specificity and variability of cortical stimulation, 39 including overlapping activations of multiple fingers due to direct cortical stimulation. 40,41 Recent studies with high density (3mm inter-electrode distance) ECoG-based stimulation have demonstrated higher degree of individual finger specificity, 42,43 although it is unclear if this approach could delineate fingertip versus more proximal finger/palm regions. Researchers have found a correlation between cortical stimulation, perception of sensation, and high gamma activity, pointing to overlap of the OFM and ECS methods.…”

Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration

“…Recently, tactile percepts in the hand have been evoked in humans through intracortical microstimulation using microelectrode arrays [10][11][12] or cortical surface stimulation using electrocorticography (ECoG) grids [13][14][15] in the primary somatosensory cortex (S1), specifically cortical area 1. Although such artificial sensory feedback helps improve the user performance with a BCI system [16], focal percepts in fingertips that would be critical for dexterous manipulations as those mentioned above [17] have been difficult to achieve.…”