Calculation of goal directed movements demonstrates a functional segregation of the cerebellar hemispheres

Introduction: The performance of a reaching movement involves the selection of the hand as an effector and the calculation of a movement trajectory in space. These calculations are performed in different parts of a fronto-parietal network. To investigate the role of the cerebellum in the preparation and execution of such a motor task, we examined the cerebro-cerebellar network while goal directed hand movements depending on different information levels given in the preparation phase with fMRI.

Methods: 16 volunteers (3-T, Siemens Trio) prepared and executed a reaching hand movement (while central fixation) with respect to varying information in the preparation phase. After presentation of a cue information regarding either the task effector (goal directed hand movement or covert shifts as a control) and/or the position in space (left or right) and an interval of 1500 ms, a go or nogo cue was presented. The visual target was pseudorandomized presented in 2 different horizontal positions (9°). Performance and central fixation was controlled with an MR-compatible infrared-oculography (Cambridge Research Systems) during the scan. Activation was determined by second level analysis using SPM 2.

Results: Full informed performance of hand movements towards the target activated cerebral foci within the motor cortex, the supplementary motor area, FEF, premotor, and parietal cortex and lobuli IV-VI and VII-VIII within the cerebellum. Preparation of the hand as the effector during the task more specifically activated the SMA and the lobuli IV-VI ipsilaterally. Location preparation more specifically activated the parietal cortex and additional foci within the cerebellar lobuli V-VI contralaterally and VIIB. Preparation of a hand movement without execution demonstrated more lateralized activation within the Lobuli IV-VI, whereas execution additionally activated medially located regions including the vermis. The lobuli VIIB-VIII were selectively engaged during the covert shift tasks with an even enhanced activation during the isolated preparation phase of the task.

Conclusion: The cerebro-cerebellar network is selectively engaged in the calculation of goal directed hand movement. Regarding the cerebellum, the transition from preparation to execution shifts activation from lateral to more medial areas in the lobuli IV-VI. The lobuli VII-VIII seem to be more involved in the calculation of space trajectories including shifts of attention.