Mesial motor areas in self-initiated versus externally triggered movementsexamined with fMRI: Effect of movement type and rate

The human frontomesial cortex reportedly contains at least four cortical ar eas that are involved in motor control: the anterior supplementary motor ar ea (pre-SMA), the posterior SMA (SMA proper, or SMA), and, in the anterior cingulate cortex, the rostral cingulate zone (RCZ) and the caudal cingulate zone (CCZ). We used functional magnetic resonance imaging (fMRI) to examin e the role of each of these mesial motor areas in self-initiated and visual ly triggered movements. Healthy subjects performed self-initiated movements of the right fingers (self-initiated task, SI). Each movement elicited a v isual signal that was recorded. The recorded sequence of visual signals was played back, and the subjects moved the right fingers in response to each signal (visually triggered task, VT). There were two types of movements: re petitive (FIXED) or Sequential (SEQUENCE), performed at two different rates : SLOW or FAST. The four regions of interest (pre-SMA, SMA, RCZ, CCZ) were traced on a high-resolution MRI of each subject's brain. Descriptive analys is, consisting of individual assessment of significant activation, revealed a bilateral activation in the four mesial structures for all movement cond itions, but SI movements were more efficient than VT movements. The more co mplex and more rapid the movements, the smaller the difference in activatio n efficiency between the SI and the VT tasks, which indicated an additional processing role of the mesial motor areas involving both the type and rate of movements. Quantitative analysis was performed on the spatial extent of the area activated and the percentage of change in signal amplitude. In th e pre-SMA, activation was more extensive for SI than for VT movements, and for fast than for slow movements; the extent of activation was larger in th e ipsilateral pre-SMA. In the SMA, the difference was not significant in th e extent and magnitude of activation between SI and VT movements, but activ ation was more extensive for sequential than for fixed movements. In the RC Z and CCZ, both the extent and magnitude of activation were larger for SI t han for VT movements. In the CCZ, both indices of activation were also larg er for sequential than for fixed movements, and for fast than for slow move ments. These data suggest functional specificities of the frontomesial moto r areas with respect not only to the mode of movement initiation (self-init iated or externally triggered) but also to the movement type and rate.