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Abstract:
The present study set out to investigate cortical
contributions to perceptual and mnemonic timing functions without
including task related motor requirements. Functional Magnetic
Resonance Tomography (fMRI) was used to scan 10 subjects while they
had to monitor temporally defined sequential structures, i.e.
rhythms, in a go/no-go paradigm. To control for influences of
presentation modality, both visual and auditory stimuli were used
in two seperate blocks. 6 gradient echo EPI images were obtained
simultaneously in 10 axial slices (6mm thick, 2mm spacing) for each
trial via 3 Tesla fMRI scanner using an event-related design. To
rule out any motor response contribution only no-go trials were
used for signal analysis. Significant BOLD activation was found for
both presentation modalities bilaterally in the medial precentral
cortex (SMA, pre-SMA), along the banks of the inferior and superior
precentral sulcus, the frontal operculum including Brocas area and
the homologue on the right side, the ascending and descending part
of the intraparietal sulcus (IPS), and the left basal ganglia
(putamen). These findings are in accordance with the assumption
that a queue of time-ordered motor commands is formed in the medial
premotor cortex before voluntary movement are executed by way of
the primary motor area. The bilaterality of activation supports the
notion that the premotor activation does not reflect motoric
effector recruitment, but a supramodal mnemonic representation of
sequences that fit into a precise timing plan.
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