P1-12. The effects of cathodal transcranial direct current stimulation of the supplementary motor area on the function of anticipatory postural adjustments

Objective: 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. This study was performed to elucidate whether cathodal transcranial direct current stimulation (tDCS) applied over the SMA modifies the function of APAs. Method: Cathodal tDCS and sham tDCS 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. Results: Following cathodal tDCS over the SMA, the ΔEMG onset between DEL_A and BF was significantly shortened compared to after sham tDCS, while tDCS over the M1 did not produce any significant effect. Conclusions: These results suggest that the SMA may play a critical role in the generation of voluntary movement accompanied by APAs. Application of cathodal tDCS over the SMA could modulate the function and timing of these APAs.