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).
