Relationship between brain activation and muscle output

The relationship between functional MRI (fMRI)-indicated brain signal and muscle output is critical in interpreting acquired data in fMRI studies and understanding the control mechanisms. To date, there are only very Limited data available to indicate such a relationship because it has previously been difficult to precisely measure muscle output (force, EMG) during fMRI experiments. Here we designed a system that could record joint force and surface EMG concurrently with fMRI data. High quality force and EMG data were obtained while the fMRI brain image quality was maintained. By using this system, we determined the relationship between fMRI-measured brain activation and handgrip force, and between fMRI-measured brain activation and EMG of finger flexor muscles of 10 human subjects. The degree of muscle activation is directly proportional to the amplitude of the brain signal determined by the fMRI measurement.