The left posterior cerebellum is involved in orienting attention along the mental number line: An online-TMS study

Although converging evidence suggests that the posterior cerebellum is involved in visuospatial functions and in the orienting of attention, a clear topography of cerebellar regions causally involved in the control of spatial attention is still missing. In this study, we aimed to shed light on this issue by using online neuronavigated transcranial magnetic stimulation (TMS) to temporarily interfere with posterior medial (Vermis lobule VII) and left lateral (Crus I/II) cerebellar activity during a task measuring visuospatial (landmark task, Experiment 1 and 2) and representational (number bisection task, Experiment 2) asymmetries in the orienting of attention. At baseline, participants showed attentional biases consistent with the literature, that is a leftward and upward bias with horizontal and vertical lines, respectively, and a leftward bias in number bisection. Critically, TMS over the left cerebellar hemisphere significantly counteracted pseudoneglect in the number bisection task, whilst not affecting attentional biases in the landmark task. In turn, TMS over the posterior vermis did not affect performance in either task. Taken together, our findings suggest that the left posterior cerebellar hemisphere (but not the posterior vermis) is a critical node of an extended brain network subtending the control of spatial attention, at least when attention needs to be allocated to an internal representational space and a certain degree of mental manipulation is required (as in the number bisection task).