Fig. 1.

Intrinsic measures of synchronization correlate with the size of stimulation-evoked responses. (A) Evoked responses to subdural electrical stimulation were used to directly infer cortical excitability. The plot shows a representative example of the mean evoked response from one electrode of patient 1. Excitability is reflected by the size of the evoked potential and was quantified as the absolute difference A between positive and negative maxima of the evoked response. Electrical stimulation was continuously applied (approx. 0.3 Hz) for multiple hours, allowing continuous measurement of cortical excitability. Unperturbed segments before the stimulation (gray bar) were used to calculate synchronization R across different electrodes. (B) Time course of stimulation-evoked response A and synchronization R of ongoing cortical activity over multiple hours in patient 1. Each black dot corresponds to a stimulation block (i.e., 10 min). (C) Evoked response amplitude A and synchronization R are highly correlated across broad frequency bands. Black line shows linear regression, $R^2$ reflects the goodness of fit. (D) Summary results of linear regression analysis ($R^2$ values, **P ≤ 0.001) for different frequency ranges of patient 1 and patient 2.