Time-course of MEP amplitude changes postintervention. The primary TMS intervention at OPT resulted in a significant increase in MEP amplitude postintervention (P < 0.001), whereas control experiments showed that IDIs shorter or longer than LCD did not result in LTP-like plasticity, indicating that LCD facilitates synaptic plasticity in human M1. The average MEP over 31 min postintervention relative to preintervention baseline was 147% ± 4% at OPT, 105% ± 4% at OPT − 50, 108% ± 3% at OPT + 50, and 105% ± 5% in the OPT − SP condition (see inset). *P < 0.05, **P < 0.01 (post hoc t-tests, significant difference of TS MEP amplitude from baseline).