Experimental design. To assess strengths of the target synapses before (Before) in addition to 10 minutes (After[1]) and 60 minutes (After [2]) after ccPAS, spTMS was delivered to the left M1 while extracting ccEPs from the right M1 (main experiment). In additional runs (not shown), spTMS was delivered to the right M1 while extracting ccEPs from the left M1 at the Before/After[1] / After[2] time points (control experiment for directionality). The ccPAS modulation consisted of delivering 180 TMS pulse pairs at a rate of 0.2 Hz, when the first pulse was delivered to the left M1 and the second pulse to the right M1, with asynchronies of 14 milliseconds, 9 milliseconds, or 4 milliseconds, on separate visits. Spatial extent of the TMS activations was estimated from the TMS-induced E-fields (red) that were also used for extracting the ccEPs from the right M1 (main experiment) and left M1 (control experiment for directionality). [Color figure can be viewed at www.neuromodulationjournal.org]