Non-invasive stimulation of the motor cerebellum has potential cognitive confounds

Transcranial stimulation techniques are increasingly used to modulate cerebellar functions, usually relating to motor control. However, the cerebellum is not only involved in motor control, but also in cognitive functions. An important, but often ignored, fact is that these cognitive cerebellar areas overlie the motor cerebellum - as such, any stimulation targeting the "motor" cerebellum would have to first pass through the "cognitive" cerebellum. In this piece, we argue that anatomical constraints and limitations of the presently available transcranial stimulation techniques make it impossible for cerebellar motor regions to be affected independently from cerebellar cognitive regions. This has considerable repercussions for the correct interpretation of studies of non-invasive stimulation applied to the cerebellum.