Independent neural control of rhythmic sequences--behavioral and fMRI evidence

Can the temporal structure of movement sequences can be represented and learned independently of their ordinal structure? Are some brain regions particularly important for temporal sequence performance? We addressed these questions in behavioral and functional magnetic resonance imaging (fMRI) experiments. Using a learning transfer design, we found evidence for independent temporal representations: learning a spatiotemporal sequence facilitated learning its temporal and ordinal structure alone; learning a temporal and an ordinal structure facilitated learning of a sequence where the two were coupled. Secondly, learning of temporal structures was found during reproduction of sequential stimuli with random ordinal structure, suggesting independent mechanisms for temporal learning. We then used fMRI to investigate the neural control of sequences during well-learned performance. The temporal and ordinal structure of the sequences were varied in a 2x2 factorial design. A dissociation was found between brain regions involved in ordinal and temporal control, the latter mainly involving the pre-supplementary motor area, the inferior frontal gyrus, the precentral sulcus, and the superior temporal gyri. In a second fMRI experiment, temporal sequences were performed with the left or right index fingers, or using rhythmic speech. The overlap in brain activity during performance with the different effectors included a similar set of brain regions to that found in the first fMRI experiment: the supplementary motor area and the superior temporal and inferior frontal cortices. We suggest that these regions are important for abstract, movement-independent temporal sequence control. This organization may be important for flexibility in voluntarily timed motor tasks.