Context-dependent relationship in high-resolution micro-ECoG studies during finger movements

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The activation of the sensorimotor cortex as measured by electrocorticographic (ECoG) signals has been correlated with contralateral hand movements in humans, as precisely as the level of individual digits. However, the relationship between individual and multiple synergistic finger movements and the neural signal as detected by ECoG has not been fully explored. The authors used intraoperative high-resolution micro-ECoG (µECoG) on the sensorimotor cortex to link neural signals to finger movements across several context-specific motor tasks.


Three neurosurgical patients with cortical lesions over eloquent regions participated. During awake craniotomy, a sensorimotor cortex area of hand movement was localized by high-frequency responses measured by an 8 × 8 µECoG grid of 3-mm interelectrode spacing. Patients performed a flexion movement of the thumb or index finger, or a pinch movement of both, based on a visual cue. High-gamma (HG; 70–230 Hz) filtered µECoG was used to identify dominant electrodes associated with thumb and index movement. Hand movements were recorded by a dataglove simultaneously with µECoG recording.


In all 3 patients, the electrodes controlling thumb and index finger movements were identifiable approximately 3–6-mm apart by the HG-filtered µECoG signal. For HG power of cortical activation measured with µECoG, the thumb and index signals in the pinch movement were similar to those observed during thumb-only and index-only movement, respectively (all p > 0.05). Index finger movements, measured by the dataglove joint angles, were similar in both the index-only and pinch movements (p > 0.05). However, despite similar activation across the conditions, markedly decreased thumb movement was observed in pinch relative to independent thumb-only movement (all p < 0.05).


HG-filtered µECoG signals effectively identify dominant regions associated with thumb and index finger movement. For pinch, the µECoG signal comprises a combination of the signals from individual thumb and index movements. However, while the relationship between the index finger joint angle and HG-filtered signal remains consistent between conditions, there is not a fixed relationship for thumb movement. Although the HG-filtered µECoG signal is similar in both thumb-only and pinch conditions, the actual thumb movement is markedly smaller in the pinch condition than in the thumb-only condition. This implies a nonlinear relationship between the cortical signal and the motor output for some, but importantly not all, movement types. This analysis provides insight into the tuning of the motor cortex toward specific types of motor behaviors.

ABBREVIATIONS BCI = brain-computer interface; BOLD = blood oxygen level dependent; ECoG = electrocorticography; fMRI = functional MRI; HG = high gamma; KNN = K nearest neighbor; µECoG = micro-ECoG.

Article Information

Correspondence Chao-Hung Kuo: University of Washington, Seattle, WA.

INCLUDE WHEN CITING Published online April 26, 2019; DOI: 10.3171/2019.1.JNS181840.

Disclosures Dr. Wander reports being an employee of Microsoft.

© AANS, except where prohibited by US copyright law.



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    To localize the central sulcus intraoperatively after craniotomy, the operative field (A, marked by a dashed-line circle) and central sulcus (round-dot line) were compared with MR angiogram (B) under intraoperative navigation. A µECoG grid (marked by a square) was placed over the sensorimotor cortex of the hand for signal recording (C). Resistive strips of the dataglove were selected to represent each digit (D). The blue lines locate thumb-related strips: interphalangeal joint, metacarpal joint, and interphalangeal space. The red lines locate index finger–related resistive strips over the distal interphalangeal, proximal interphalangeal, and metacarpal joints. Figure is available in color online only.

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    Cortical activation in different states for each of 3 patients: each square of the grid represents a microgrid electrode; color intensity represents strength of cortical activation relative to rest. Cortical activation relative to the resting state was calculated by t-statistic (more activated, light yellow; less activated, dark blue). Half of the channels with noise were eliminated from case 2. Figure is available in color online only.

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    µECoG and glove signals of patient 2 in different movement states. Row 1: µECoG signals of thumb- and index finger–associated electrodes under different behavioral conditions. Thumb- and index finger–associated electrode signals were both similar to those of isolated thumb-only and index-only movement and pinch. Row 2: Glove signals for average of thumb strips. Row 3: Glove signals for average of index finger strips. The thumb glove signal was less active in the pinch movement than in the thumb-only movement. The index-finger glove signals were similar in the pinch and index-only movements. Figure is available in color online only.

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    Correlation was used to compare the µECoG signal from thumb-only or index-only electrodes with thumb-only and index-only glove signals. Data were clustered by 3 different groups corresponding to each different movement (blue, thumb-only; red, index-only; green, pinch). A linear polynomial model was calculated for each group (dotted line, thumb-only; dashed line, index-only; solid line, pinch). For the thumb (A), the glove signal change in pinch was lower than that in the thumb-only movement. There was no change between the µECoG signal in the thumb-only and pinch movements. However, for the index finger (B), the µECoG and glove signal changes in the pinch and index-only movements were similar. Figure is available in color online only.

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    Comparison of peak values of µECoG and glove signals in different movement states (rest, thumb-only, index-only, and pinch). Both µECoG and glove signals in thumb-only and index-only movement were statistically significantly higher than in rest (p < 0.05 in each case). In pinch, the µECoG signal of the thumb was similar to that in the thumb-only movement (A, p > 0.05). However, for the glove signal, the peak value in the pinch was lower than that in thumb-only movement (B, all p < 0.05). For the index finger, the peak value of the µECoG signal in the pinch was similar to (case 1 and 3, p > 0.05) or higher than (case 2, p < 0.05) that in the index-only movement (C). For the glove signal, there was no statistically significant difference in the peak value between the pinch and index-only movement (D, all p > 0.05).





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