Article Figures & Data
Figures
- Figure 1.
Representative spectral changes in a single electrode from motor cortex. In response to visual cues, subject 6 repeatedly flexed and extended different fingers of his contralateral hand. Samples of the normalized PSD of the potential timeseries were calculated from 1 s windows centered at times of maximum flexion and also during rest. A, Normalized PSD samples were naively decomposed using a principal component approach to characterize covariation in power at different frequencies. The elements of the first principal spectral component (first PSC, pink) are non-zero across all frequencies, consistent with change in a power-law in the cortical power spectral density. The second PSC (gold) is peaked between 15 and 25 Hz (β rhythm range). The third PSC (yellow) is a 0–10 Hz (θ,α) peak. (4th − 179th PSCs not shown). B, Projection magnitudes to each spectral sample from the first (top) and second (bottom) PSCs, sorted by movement type; black indicates samples from rest periods. Therefore, each such sample, denoted by a dot, corresponds to the contribution of a PSC to the PSD from a one second epoch flanking a single movement, and there are several such movements in response to a single cue. Note that the first PSC has a specific increase from rest for index finger movements, and, to a lesser degree, for middle finger. The second PSC shows decrease from rest for all finger types. C, Mean PSD of index finger movement samples (dark green) and rest samples (black). D, Average time-varying PSD (scaled as percentage of mean power at each frequency) with respect to first index finger movement from each movement cue (N = 30). E, Mean of reconstructed PSD samples from the same electrode, and (F) average reconstructed time-varying PSD, with second and third PSC omitted. This is consistent with the increase in the amplitude of a power law with local cortical activity. G, Mean of reconstructed PSD samples, and (H) average reconstructed time-varying PSD, using only second and third PSCs. This is consistent with a change in the α and β rhythms. Note that C = E + G and D = F + H. These findings generalize across all subjects and electrodes (supplemental Fig S4, available at www.jneurosci.org as supplemental material).
- Figure 2.
Capturing local cortical activity; individual digit representation in adjacent electrodes in subject 1. A, The position of each finger was measured using a transducing glove during cued flexion-extension. B, Axes, The maximum squared cross-correlation (r2) between sample projection weights to the first PSC, for each electrode, between any single movement type and rest, illustrates sparse digit representation (supplemental Figs. S4–6, available at www.jneurosci.org as supplemental material). Corresponding locations are shown in x-ray. Each of these shows specificity for a different type of finger movement, and the color code redundancy between the electrodes in B–K and digit movement type in A reflects this. C, Left, First (pink) and second (gold) PSCs generated from finger movements and rest, for the electrode shown in dark blue in the x-ray inset in B. Middle, As in Figure 1B. Right, Mean projection magnitudes for each finger type, with mean from rest samples subtracted. Error bars indicate ± 3 times the SE (3σ) of the mean (right most: rest samples). The upper bars represent the first PSC, and the lower are for the second. D, E, As in C, but for the dark green (D) and light blue (E) electrodes. F, H, J, Traces of thumb, index, and little finger position for a 40 s period. G, I, K, Projections of the time-frequency representation to the first PSC, “C1(t)”, for each of the three electrodes for same 40 s. Each electrode is specifically and strongly correlated with one movement type (r = 0.46 C1(t) from dark blue electrode-thumb; r = 0.47 green electrode-index finger; r = 0.29 light blue electrode-little finger; cross-combinations had a mean correlation of −0.09, indicating light hyperextension of other fingers while flexing the appropriate finger in this subject), over 10 min of continuous data (3.6 × 106 samples).
- Figure 3.
First PSC projection magnitudes, at three surface electrodes. A, Mean of projection magnitudes in three electrodes of samples for each finger movement class, after subtraction of the mean of the rest time samples, for subject 2 (as in the right-hand column of insets C–E in Fig. 2). The color of the dots flanking axes indicate corresponding electrode on the cortical schematic. Redundancy in color between electrode color and movement type is meant to provide intuitive relation, but also indicates electrode-movement type pairings used for analysis. B–D, Same as A, but for subjects 3–5 (B, subject 3; C, subject 4; D, subject 5).
- Figure 4.
Correlation between the time course of the first PSC (C1(t)) and finger position. A, A single trial showing C1(t) in an associated electrode and thumb movement, demonstrating delay from the cortex to movement onset, from subject 10. B, Correlation in the electrode-movement pair from A as a function of latency between the two, over the full 10 min period. C, The correlation between C1(t) and paired finger movement was 0.37 (SD = 0.16, N = 24) across eight of the subjects, three electrodes each (subjects 2 and 8 excluded, because their movement-associated cortical change was poorly separated; supplemental Fig. S7, available at www.jneurosci.org as supplemental material). D, The mean latency between C1(t) and finger movement was 84 ms (SD = 39 ms, N = 24).
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Supplemental Data
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