In my recent work I have observed two MEPs in response to single-pulse TMS, as shown in the attached figure from one muscle of one participant. I have observed these in the medial and lateral hamstring muscles in ~40% of participants. The latency of the second response is ~55-60 ms. Can anyone please guide me on where to look for information on these responses? For example, any previous reports of long-latency MEPs, or papers suggesting potential pathways underlying these responses.