Decoding hand gestures from primary somatosensory cortex using high-density ECoG

Abstract

Electrocorticography (ECoG) based Brain-Computer Interfaces (BCIs) have been proposed as a way to restore and replace motor function or communication in severely paralyzed people. To date, most motor-based BCIs have either focused on the sensorimotor cortex as a whole or on the primary motor cortex (M1) as a source of signals for this purpose. Still, target areas for BCI are not confined to M1, and more brain regions may provide suitable BCI control signals. A logical candidate is the primary somatosensory cortex (S1), which not only shares similar somatotopic organization to M1, but also has been suggested to have a role beyond sensory feedback during movement execution. Here, we investigated whether four complex hand gestures, taken from the American sign language alphabet, can be decoded exclusively from S1 using both spatial and temporal information. For decoding, we used the signal recorded from a small patch of cortex with subdural high-density (HD) grids in five patients with intractable epilepsy. Notably, we introduce a new method of trial alignment based on the increase of the electrophysiological response, which virtually eliminates the confounding effects of systematic and non-systematic temporal differences within and between gestures execution. Results show that S1 classification scores are high (76%), similar to those obtained from M1 (74%) and sensorimotor cortex as a whole (85%), and significantly above chance level (25%). We conclude that S1 offers characteristic spatiotemporal neuronal activation patterns that are discriminative between gestures, and that it is possible to decode gestures with high accuracy from a very small patch of cortex using subdurally implanted HD grids. The feasibility of decoding hand gestures using HD-ECoG grids encourages further investigation of implantable BCI systems for direct interaction between the brain and external devices with multiple degrees of freedom.

mano: A Wearable Hand Exoskeleton for Activities of Daily Living and Neurorehabilitation

“…Such results have been confirmed in invasive [23] and non-invasive [24] studies. It has also been shown that passive hand mobilizations induce similar brain patterns as those observable in active manual tasks [25].…”

Sub-millimeter ECoG pitch in human enables higher fidelity cognitive neural state estimation

“…These proof of concept technologies have enabled neurophysiologists to discover novel neural dynamics from the surface of the brain, including recurrent spiral waves manifested from seizures in animal model (Viventi et al, 2011) and single unit activity in both animal model and studies in the clinic (Khodagholy et al, 2016(Khodagholy et al, , 2014. These developments could lead to advances in basic neuroscience research and medical applications such as clinical mapping and brain-machine interfaces (Blakely et al, 2008;Bleichner et al, 2016;Branco et al, 2016;Chang, 2015;Ganji et al, 2017;Hwang and Andersen, 2013;Jiang et al, 2017;Kaiju et al, 2017;Kellis et al, 2010;Leuthardt et al, 2009;Maharbiz et al, 2017;Muller et al, 2016b).…”

Visual epidural field potentials possess high functional specificity in single trials

“…A more significant factor determining the specificity of EFP/ECoG signals, therefore, might be given by the size and density of the recording electrodes. Only few studies have compared signal quality and decoding performance for the different types of subdural and intracortical arrays used in clinical and basic neuroscience studies (Kellis et al, 2016;Flint et al, 2017;Wang et al, 2017), yet it appears that many of the results indicating high signal specificity were obtained with high-density arrays and rather small electrodes (Kaiju et al, 2017;Branco et al, 2017;Hu et al, 2018;Ramsey et al, 2018). The findings of the present study that EFPs possess high spatial selectivity is clearly in line with this: With the small electrodes of our array we estimated mean ERF sizes of about 2.7 and 2.8 deg diameter (re-calculated from ERF areas assuming circular ERFs) in monkeys M1 and M3, respectively, and 4.0 deg in M2, which is around a factor of 1.6 to 2.3 of the receptive field size of intracortical LFPs, measured with the same mapping paradigm (Drebitz et al, 2019).…”