Fig. 2: Signaling directionality and connection excitability.

a Calculation of the directionality index (DI) based on signaling probabilities (%) in three example connections (rows) probed >200 times (#) over days in either direction (columns). For each connection, stimulation on either side is at the arrowtail and the response at the arrowhead. Average significant (blue) and non-significant (gray) trials are overlaid and plotted against the same scale. Note how signaling across connections over time can be reciprocal (top), fully asymmetric (bottom), or intermediary (middle), as quantified by the DI. b Distribution (probability density function against the x-axis), median (full line) and IQR (dashed) of signaling probabilities (left blue half-violin) and absolute DI (right green half-violin) in three classes of connections: local (preset <25 mm) and long-range (≥25 mm) short-latency (<65 ms, see Fig. 1d) and long-latency (≥65 ms) connections across brain regions. c Calculation of the excitability index (ExI) based on examples of response magnitude growing with stimulation intensity (0.2 to 12 mA, black to red gradient) shown as the mean iEEG cortical response (top left). The corresponding linelength transform (top right) quantifies the response magnitude in a stimulation-response curve (bottom), whose area-under-the-curve is the excitability index. d Distribution, median (full line) and IQR (dashed) of the ExI across a subset (# total number) of local and long-range effective connections tested with a two-sided Wilcoxon rank-sum test. e Two-sided Pearson correlation tested between the ExI and the signaling probability for the subset of connections in d.