Plasticity induction in the pre-supplementary motor area (pre-SMA) and SMA-proper differentially affects visuomotor sequence learning

Abstract

BackgroundBoth pre-supplementary motor area (pre-SMA) and SMA-proper (SMA) must play important roles in visuomotor sequence learning. However, functional differences between the pre-SMA and SMA have not been well studied in humans. ObjectiveTo elucidate the functional differences between the pre-SMA and SMA in sequence learning in humans. MethodsTo induce LTP/LTD, we administered quadripulse transcranial magnetic stimulation (QPS) with an inter-stimulus interval of 5 or 50 ms (QPS-5/50) over the pre-SMA or SMA in healthy volunteers. The sham stimulation was also done as a control. We studied the effects of LTP/LTD in the pre-SMA/SMA on a new sequence learning and the performance of well-learned sequence by using sequence learning task called the “2 × 10 task”. Effects on the simple choice reaction time task were also studied for comparison. ResultsQPS-5 over the pre-SMA increased the error rate without any changes in movement speed. When administered over the SMA, QPS-5 decreased, and QPS-50 increased the rate of reaction time reduction across trials without changes in the error rate. QPS over neither the pre-SMA nor SMA affected the performances of a well-learned sequence or a simple choice reaction time task. ConclusionsOur findings that QPS over the pre-SMA correlated with sequence learning performance and that over the SMA with execution speed are consistent with the previous results in animals and humans. Our results lend further support to the utility of QPS for modulating motor learning in humans.