Comparing motion- and imagery-related activation in the human cerebellum: a functional MRI study.

Cerebellar activation during execution and imagination of a finger movement was compared. Functional magnetic resonance imaging was used to detect cerebellar activation during execution and imagination of an untrained self-paced finger-to-thumb movement (left and right hand separately). The four fingers were opposed to the thumb in changing sequences freely chosen by the subjects. The activation maps of 10 right-handed healthy subjects were averaged after transformation into a common coordinate space. Averaged activation maps revealed strong motion-related bilateral activation in the anterior lobe of the cerebellum and in the paravermal regions of the posterior lobe. Ipsilateral activity predominated significantly. Compared to motion, imagination of the same task produced lower signal changes, and foci were more variable in position and strength. The averaged activation maps showed activity in the same regions as in motion. Activation in the posterior cerebellar lobe was more prominent extending into the lateral hemispheres. Ipsilateral dominance was significant for right-hand imagery. The left-hand task only showed marginally stronger ipsilateral activation. The activation pattern observed during execution of the finger-to-thumb movement is in agreement with theories of functional cerebellar topography. For imagery, activation at a comparable location may reflect common functionality, e.g., motor preparation and/or timing. Additional activation in the lateral hemispheres may be related to an imagery-specific function.