Primary Motor Cortex is Causally Involved in Mental Rotation of Abstract Figure and Hands: a TMS study

Activation of primary motor cortex (M1) has been observed in some neuroimaging studies ofmental rotation (MR). However, the functional relationship between M1 and MR remainsunclear. Multiple studies suggest that M1 has a causal relationship with MR, while otherspropose that M1 activation is merely an effect of other brain regions’ activities. The presentstudy utilises a neural noise Transcranial Magnetic Stimulation (TMS) approach to investigatethe relationship between M1 and MR. Sixty participants, both male and female, with agesranging from 18 to 30, were equally divided into two experimental groups, each performing MRtasks of either Shepard figures or hands. They were presented with side-by-side stimuli and wereinstructed to determine whether they are identical or mirror images of each other. Theexperiment was divided into six experimental blocks comprised of randomised identical andmirrored stimuli. A real TMS was applied on odd blocks and a sham TMS was applied on evenblocks. Average mean RTs for TMS and sham blocks for both hands and Shepard figures wereobtained and compared using a one-tailed paired samples t-test. A significant mean RTdifference between TMS and sham conditions would be suggestive of an M1 and MR causalrelationship. A significant difference was found between sham and TMS trials in the handscondition (p = .002) and the Shepard Figures condition (p < .001). This suggests that M1 has acausal role in MR performance of both hands and Shepard Figures.Keywords: primary motor cortex, mental rotation, transcranial magnetic stimulation