An electrocorticographic brain interface in an individual with tetraplegia

Abstract

Brain-computer interface (BCI) technology aims to help individuals with disability to control assistive devices and reanimate paralyzed limbs. Our study investigated the feasibility of an electrocorticography (ECoG)-based BCI system in an individual with tetraplegia caused by C4 level spinal cord injury. ECoG signals were recorded with a high-density 32-electrode grid over the hand and arm area of the left sensorimotor cortex. The participant was able to voluntarily activate his sensorimotor cortex using attempted movements, with distinct cortical activity patterns for different segments of the upper limb. Using only brain activity, the participant achieved robust control of 3D cursor movement. The ECoG grid was explanted 28 days post-implantation with no adverse effect. This study demonstrates that ECoG signals recorded from the sensorimotor cortex can be used for real-time device control in paralyzed individuals.

Figure 1. High-density ECoG grid location and ECoG signal modulation during motor screening tasks.

(a) Layout of the recording (gray, brain-facing), reference (red, dura-facing), and ground (green, dura-facing) electrodes. (b) ECoG electrode location mapped to a 3D rendering of the participant's brain. Red dots represent ECoG electrodes, and Electrodes 1 and 32 are labeled to indicate grid orientation. The black arrow indicates the central sulcus (CS) of the left hemisphere. (c) Modulation of ECoG signals by attempted hand opening/closing (left column) and elbow flexion/extension (right column) for Channel 4 (top row) and Channel 7 (bottom row). These four time-frequency plots show data averaged over 24 trials. Black sinusoidal curves overlaid on all plots represent the normalized instructed joint angles. Time 0 is the onset of visual cues (hand fully-open, elbow fully-extended). Color represents pseudo z-scores, indicating changes from baseline condition, and color axes of all plots have the same range. Red and blue colors indicate increases and decreases in spectral power, respectively. High-gamma band (70–110 Hz) powers increased for Channels 4 and 7 during attempted hand and elbow movements, respectively. Also, for both channels, the high-gamma band power differed between attempted hand and elbow movements. (d) Cortical activity patterns across all 28 recording electrodes during attempted hand and elbow movements represented by 70–110 Hz band power over the 10-second movement time averaged across 24 trials. The color bars represent pseudo z-scores. Cortical activity patterns differed between hand and elbow movements.

Figure 2. BCI control performance across days.

BCI control success rate and computer assist level over time. Success rates are shown for 16-trial blocks of brain control. Alternating white and light-purple zones mark individual days, while vertical green lines mark the occurrence of neural decoder adaptation. Days 16, 22, and 23 were planned days off.

Figure 3. ECoG signal modulation and brain-controlled cursor movement trajectories during 2D (176 trials) and 3D (80 trials) cursor movements.

(a) Time-frequency plots of Channel 4 for eight targets during 2D cursor movement. Time 0 represents target onset, and the color represents change from baseline. (b) Cursor trajectories averaged over successful trials (center plot) and individual trajectories of all trials during 2D cursor movement. (c, d) Cursor trajectories averaged over successful trials for the front and back targets, respectively, for 3D cursor movement. (e, f) The 95% confidence intervals of cursor trajectories of all trials for the front and back targets, respectively, for 3D cursor movement. For all trajectory plots in this figure, the circles/spheres show the effective target size, i.e. their radii equal the sum of radii of the target and cursor balls. The unit of the x, y, and z-axes is in percentage of the workspace.