Cerebellar control of preparing and executing eye and hand movements

Introduction:

Hand/finger or combined eye-hand movements are known to activate a cerebellar network consisting of the cerebellar lobuli IV-VI and VII-VIII including the vermis. These movements are performed by anatomically different effectors and functionally segregated by different phases of planning and executing a movement. We used fMRI to differentiate these subcomponents within the known activated cerebellar network.

Methods:

Task design in part 1 consisted of preparation and execution of combined and isolated eye-hand movements towards a visually presented target (12 volunteers). The tasks were differentiated by using a go/nogo design after a visual cue regarding information about the task effector (eye/hand) followed 1500 ms later by the go/nogo command. Part 2 focused on a temporal component. Visually triggered index to thumb opposition was performed 1 s after a visual cue was presented (12 subjects). The performance was registered online by contact and therefore temporally assignable. Analysis of image-data was calculated for different time-points in relation to the go-signal (for preparation -1500 ms, execution, execution + 1500 ms setoff). Calculations including ANOVAS to differentiate the subcomponents were done using SPM8.

Results:

Execution of eye-hand movements activated a cerebellar network including the lobuli HIV-VI bilaterally, the vermis, and lobuli within the posterior hemispheres extending into Crus I/II with different anatomical peaks regarding the hand (more ipsilateral, lobules IV-VI) and eye (more vermal) components. Preparation of the hand movement activated the lobuli IV-VI with a shift to the lateral parts of the lobuli and almost lacked vermal activation. Preparation of saccades also showed a lateral shift including vermal activation. A similar lateral shift especially within the lobuli IV-VI demonstrated the analysis of the preparatory phase of finger opposition movements that otherwise produced an activation pattern comparable to the hand movements.

Conclusion:

The activation foci within the cerebro-cerebellar network consist of different subcomponents. Besides the anatomical aspect that already could be defined by a somatotopical organization in the cerebellum, the transition from preparation to execution is related to shifts of activation from lateral to more medial areas especially in the lobuli IV-VI suggesting a further functional subdivision within the somatotopically organized foci.