title: Different Effects of Implicit and Explicit Motor Sequence Learning on Latency of Motor Evoked Potential Evoked by Transcranial Magnetic Stimulation on the Primary Motor Cortex.
abstract: Motor training induces plastic changes in the primary motor cortex (M1). However, it is unclear whether and how the latency of motor-evoked potentials (MEP) and MEP amplitude are affected by implicit and/or explicit motor learning. Here, we investigated the changes in M1 excitability and MEP latency induced by implicit and explicit motor learning. The subjects performed a serial reaction time task (SRTT) with their five fingers. In this task, visual cues were lit up sequentially along with a predetermined order. Through training, the subjects learned the order of sequence implicitly and explicitly. Before and after the SRTT, we recorded MEP at 25 stimulation points around the hot spot for the flexor pollicis brevis (FPB) muscle. Although no changes in MEP amplitude were observed in either session, we found increases in MEP latency and changes in histogram of MEP latency after implicit learning. Our results suggest that reorganization across the motor cortices occurs during the acquisition of implicit knowledge. In contrast, acquisition of explicit knowledge does not appear to induce the reorganization based on the measures we recorded. The fact that the above mentioned increases in MEP latency occurred without any alterations in MEP amplitude suggests that learning has different effects on different physiological signals. In conclusion, our results propose that analyzing a combination of some indices of M1 excitability, such as MEP amplitude and MEP latency, is encouraged in order to understand plasticity across motor cortices.
authors.affiliation: Human Motor Control Laboratory, Graduate School of Integrated Arts and Sciences, Hiroshima UniversityHiroshima, Japan; Japan Society for the Promotion of ScienceTokyo, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Hirano
authors.affiliation: Human Motor Control Laboratory, Graduate School of Integrated Arts and Sciences, Hiroshima UniversityHiroshima, Japan; Japan Society for the Promotion of ScienceTokyo, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Kubota
authors.affiliation: Human Motor Control Laboratory, Graduate School of Integrated Arts and Sciences, Hiroshima University Hiroshima, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Koizume
authors.affiliation: Human Motor Control Laboratory, Graduate School of Integrated Arts and Sciences, Hiroshima University Hiroshima, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: Human Motor Control Laboratory, Graduate School of Integrated Arts and Sciences, Hiroshima University Hiroshima, Japan.
authors.forename: Kozo
authors.initials: K
authors.lastname: Funase
keywords: MEP latency; TMS; explicit learning; implicit learning; motor cortex