The role of higher-order motor areas in voluntary movement as revealed by high-resolution EEG and fMRI

In the human motor cortex structural and functional differences separate mo tor areas related to motor output from areas essentially involved in higher -order motor control. Little is known about the function of these higher-or der motor areas during simple voluntary movement. We examined a simple fing er flexion movement in six healthy subjects using a novel brain-imaging app roach, integrating high-resolution EEG with the individual structural and f unctional MRI. Electrical source reconstruction was performed in respect to the individual brain morphology from MRI. Highly converging results from E EG and fMRI were obtained for both executive and higher-order motor areas. All subjects showed activation of the primary motor area (MI) and of the fr ontal medial wall motor areas. Two different types of medial wall activatio n were observed with both methods: Four of the subjects showed an anterior type of activation, and two of the subjects a posterior type of activation. In the former, activity started in the anterior cingulate motor area (CMA) and subsequently shifted its focus to the intermediate supplementary motor area (SMA), Approximately 120 ms before the movement started, the intermed iate SMA showed a drop of source strength, and simultaneously MI showed an increase of source strength. In the posterior type, activation was restrict ed to the posterior SMA. Further, three of the subjects investigated showed activation in the inferior parietal lobe (IPL) starting during early movem ent preparation. In all subjects showing activation of higher-order motor a reas (anterior GMA, intermediate SMA, IPL) these areas became active before the executive motor areas (MI and posterior SMA). We suggest that the earl y activation of the anterior CMA and the IPL may be related to attentional functions of these areas. Further, we argue that the intermediate part of t he SMA triggers the actual motor act via the release of inhibition of the p rimary motor area. Our results demonstrate that a noninvasive, multimodal b rain imaging technique can reveal individual cortical brain activity with h igh temporal and spatial resolution, independent of a priori Physiological assumptions. (C) Academic Press.