Time-resolved fMRI of activation patterns in M1 and SMA during complex voluntary movement

The aim of this study was to use time-resolved functional magnetic resonanc e imaging (fMRI) to investigate temporal differences in the activation of t he supplementary motor area (SMA) and the primary motor cortex (M1). We rep ort data from eight human volunteers who underwent fMRI examinations in a 1 .5T Philips Gyroscan ACS-NT MRI scanner. While wearing a contact glove, sub jects executed a complex automated sequence of finger movements either spon taneously or in response to external auditory cues. Based on the result of a functional scout scan, a single slice that included the M1 and the SMA wa s selected for image acquisition (echo planar imaging, repetition time 100 ms, echo time 50 ms, 64 X 64 matrix, 1,000 images). Data were analyzed with a shifting crosscorrelation approach using the STIMULATE program and in-ho use programs written in Interactive Data Language (IDLTM). Time-course data were generated for regions of interest in the M1 as well as in the rostral and caudal SMA. Mean time between onset of the finger movement sequence an d half-maximum of the signal change in M1 was 3.6 s for the externally cued execution (SD 0.5) and 3.5 s for the spontaneous execution (SD 0.6). Activ ation in the rostral section of the SMA occurred 0.7 s earlier than it did in the M1 during the externally cued execution and 2.0 s earlier during the spontaneous execution, a difference significant at the P < 0.01 level. Our results indicate that rostral SMA activation precedes M1 activation by var ying time intervals in the sub-second range that are determined by the mode of movement initialization. By applying a paradigm that exerts a different ial influence on temporal activation, we could ensure that the observed tim ing differences were not the result of differences in hemodynamic response function.