TMS of supplementary motor area (SMA) facilitates mental rotation performance: Evidence for sequence processing in SMA

- Online TMS was applied over SMA and M1 during the performance of mental rotation tasks.
- TMS of the SMA improves the performance for stimuli with higher angular disparity.
- SMA mediates domain-general sequence processes and acts as an accumulator.
- M1 does not play a causal role in mental rotation tasks.

In the present study we applied online transcranial magnetic stimulation (TMS) bursts at 10 Hz to the supplementary motor area (SMA) and primary motor cortex to test whether these regions are causally involved in mental rotation. Furthermore, in order to investigate what is the specific role played by SMA and primary motor cortex, two mental rotation tasks were used, which included pictures of hands and abstract objects, respectively.While primary motor cortex stimulation did not affect mental rotation performance, SMA stimulation improved the performance in the task with object stimuli, and only for the pairs of stimuli that had higher angular disparity between each other (i.e., 100° and 150°).The finding that the effect of SMA stimulation was modulated by the amount of spatial orientation information indicates that SMA is causally involved in the very act of mental rotation. More specifically, we propose that SMA mediates domain-general sequence processes, likely required to accumulate and integrate information that are, in this context, spatial. The possible physiological mechanisms underlying the facilitation of performance due to SMA stimulation are discussed.