TMS over the left angular gyrus impairs the ability to discriminate left from right

The underlying cognitive and neural mechanisms of the ability to discriminate left from right are hardly explored. Clinical studies from patients with impairments of left-right discrimination (LRD) and neuroimaging data suggest that the left angular gyrus is particularly involved in LRD. Moreover, it is argued that the often reported sex difference in LRD, with women being more susceptible to left-right errors than men, is the result of a stronger lateralization in men than women. Offline repetitive transcranial magnetic stimulation (rTMS) was used to test whether the left angular gyrus is involved in LRD and whether men have a stronger lateralization in LRD than women. Twenty-four participants (12 men, 12 women) completed a behavioral LRD task in three different conditions: after rTMS of the left and right angular gyrus and after 'sham' rTMS (control). The results revealed that after rTMS of the left angular gyrus, LRD accuracy rates were significantly reduced compared to the control condition. After rTMS of the right angular gyrus no difference to the control condition was observed. In addition, there was no overall sex difference in the LRD task and men and women were similarly affected by stimulation over the left and right angular gyrus, suggesting that the functional cerebral organization of LRD does not differ in men and women with similar LRD skills. Taken together, the findings suggest that the left angular gyrus is critically involved in LRD. It is argued that the left angular gyrus integrates spatial information with the meaning of the words 'left' and 'right', thereby assigning the labels 'left' and 'right' to a certain state or direction, etc.