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The Functional Involvement of the SMA during Intermanual Transfer of

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Recent evidence suggested that the SMA is involved in intermanual transfer of sequence knowledge in healthy humans1,2. What still remains unknown is the specific role of this region during the intermanual transfer process. One of the SMA functions during sequence learning is to encode the order of forthcoming sequences, a process that to a large extent occurs prior to movement execution3,4. Another important SMA function is to contribute to signal movement-related activity during the execution of movement5. In this study we explored the effect of timing rTMS pulses over the SMA region prior to and during the execution of a sequence of finger movements on the magnitude of intermanual transfer of sequence learning. Healthy volunteers trained for 30 min on the serial reaction time task (SRTT), which requires multifinger key presses, with their right-dominant hand. During the first 15 min of SRTT training different groups of subjects received rTMS over the SMA (1 Hz, 900 pulses, 80% RMT) or sham TMS. Each rTMS pulse was given 100 ms prior to the presentation of a GO signal to move or 400 ms after the presentation of a GO signal to move. The GO signal was indicated by an asterisk presented every 1000 ms in a computer screen located in front of them. Training with the dominant hand led to improvements in response time in the nondominant (left) hand, a process called intermanual transfer in the sham stimulation group. Response times in the left hand, during practice of the training sequence block, were decreased by rTMS stimulation over the SMA 100 ms prior to a GO signal to move. No changes in response times in the left hand were observed when the SMA region was stimulated 400 ms after a GO signal to move. These results are in agreement with previous results indicating that the SMA is involved in transfer of motor sequence learning in healthy humans. Furthermore, these findings expand those previous results indicating that the ability of the subject to predict the forthcoming sequences, a process that to a large extent occurs prior to movement execution, is a critical factor for successful intermanual transfer of sequence learning.

References:
1. Nakahara et al., 2001. J Cogn Neurosci. 2001 Jul 1;13(5):626-47.
2. Perez et al., 2007 (submitted)
3. Halsband et al. 1994 Neurosci Res. 1994 Aug;20(2):149-55.
4. Tanji and Shima 1994 Nature. 1994 Sep 29;371(6496):413-6.
5. Brinkman and Porter 1979. J Neurophysiol. 1979 May;42(3):681-709.

Last updated November 16, 2007