A 7T fMRI study of cerebellar activation in sequential finger movement tasks.

We investigated whether higher activation of the cerebellar cortex in unpredictable compared to predictable sequential finger movements reflects higher demands in motor response selection or also increases in demands on motor sequencing. Furthermore, we asked the question whether the cerebellar nuclei show a similar or reversed response profile as the cerebellar cortex. Ultra-high-field 7T functional magnetic resonance imaging was performed in nineteen right-handed, healthy young participants. Tasks involved finger tapping of a constant sequence, a random sequence, and with one finger at a time (no sequence). Conditions involved the same number of movements of fingers II-V. The three tasks were accompanied by the activation of the known hand areas within the cerebellar cortex and dentate nuclei. Activation of the cerebellar cortex and the dorsorostral dentate was significantly increased in the random-sequence condition compared to both the constant-sequence and the no-sequence conditions, with no significant difference between the constant-sequence and the no-sequence conditions. Error rate and movement frequency was not significantly different between conditions. Thus, differences between conditions cannot be explained by differences in motor execution. Because no difference was observed between the no-sequence and the constant-sequence conditions, increased cerebellar activation in the random-sequence condition likely reflects increased demands in motor response selection. Co-activation of cerebellar cortex and nuclei may be a consequence of excitatory afferent collaterals to the nuclei, "rebound-firing" of dentate neurons, and/or inhibitory synaptic input from Purkinje cells.

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