P 71. The effects of cathodal transcranial direct current stimulation of the supplementary motor area on the function of anticipatory postural adjustments

Abstract

Introduction Although the supplementary motor area (SMA) is thought to contribute to the generation of anticipatory postural adjustments (APAs), which act to stabilize supporting body segments prior to movement, its precise role remains unclear ( Jacobs et al., 2009 ). Non-invasive brain stimulation, such as transcranial direct current stimulation (tDCS), over the primary motor cortex (M1) has been shown to modulate cortical excitability, thereby influencing motor behaviour and learning. However, only a few studies have reported that application of tDCS over the SMA changes the excitability of the M1 ( Kirimoto et al., 2011 ) and motor learning process ( Vollmann et al., 2012 ). Objectives This study was performed to elucidate whether cathodal tDCS applied over the SMA modifies the function of APAs. Materials and Methods Cathodal tDCS and sham tDCS (2 mA) were applied over the SMA or left of the leg area of the M1 of 11 healthy subjects for 15 min. Subjects performed the task of self-paced rapid shoulder flexion before, immediately after, and 15 min after tDCS. Electromyographic (EMG) activity was recorded from the deltoid anterior (DEL_A), as the prime mover muscle, and biceps femoris (BF), as the postural muscle during tasks. Latency differences (ΔEMG onset) with the two types of stimuli were calculated by subtracting the EMG burst onset of the BF from that of the DEL_A. Results Fig. 1 shows the EMG waveforms obtained from a representative subject before, immediately after, and 15 min after cathodal tDCS over the SMA. Following cathodal tDCS over the SMA, the ΔEMG onset was significantly shortened compared to after sham tDCS, while tDCS over the M1 did not produce any significant effect. Conclusion These results suggest that the SMA may play a critical role in the generation of voluntary movement accompanied by APAs. As the application of cathodal tDCS over the SMA could modulate EMG activity, anodal tDCS over the SMA could have beneficial effects in patients with Parkinson’s disease who have deficient APAs [Latash et al., 1995] . Acknowledgement of funding sources This work was supported in part by a Grant-in-Aid for Scientific Research (C) No. 08042773 from the Japan Society for the Promotion of Science and a research grant from Niigata University of Health and Welfare.