Cerebellar contributions to working memory

Anatomical studies show the existence of two well-characterized cortico-cerebellar 'loops' that connect prefrontal and cortical motor areas each with their own modules in the cerebellar cortex. The involvement of the cerebellar 'motor' modules in motor skills is well established, but little is understood about the way that cerebellar prefrontal modules process information from the prefrontal cortex. This question is particularly important for understanding the human cortico-cerebellar system because the prefrontal loop appears to have expanded significantly during the course of evolution. Here, we investigate whether cerebellar modules known to be connected with the prefrontal cortex (specifically within cerebellar cortical lobule VII) become engaged by the execution of skilled cognitive operations. We tested the anatomically specific hypothesis that this area would be activated by the skilled maintenance and manipulation of items within verbal working memory. We used the Paced Auditory Serial Addition Test (PASAT) in combination with a sparse sampling method to avoid artefact caused by speech-related head movement on the BOLD timecourse. Consistent with our hypothesis, we report that activity in the experimental condition was evoked in medial portions of cerebellar cortical lobule VII (relative to a closely matched control task). As would be anticipated, the motor demands common to experimental and control tasks activated face areas of the motor cortex as well as connected motor areas of the cerebellar cortex. We discuss this evidence in the context of theories of cortico-cerebellar information processing.