Differential representation of dynamic and static power grip force in the sensorimotor network

Previous studies investigating the blood oxygen level-dependent (BOLD) signal in the human sensorimotor cortex during static force (maintained for a few seconds) and dynamic force (repetitive force pulses) resulted in contradictory findings. Therefore, we conducted a whole-brain functional magnetic resonance imaging study during a visuomotor task requiring the production of either dynamic or static power grip force. Thereby we aimed at clarifying whether the BOLD signal behaves differently with dynamic and static force in the primary motor cortex, and whether it behaves in the same way in all areas and regions involved in force production. In the static condition, participants applied visually guided, isometric grip force on a dynamometer of 20% maximal voluntary contraction (MVC) and held this force for 21 s. In the dynamic condition, self-paced force pulses of 20% MVC were produced at a rate of 0.5 Hz. Static and dynamic force production activated an overlapping network of sensorimotor cortical and subcortical regions. However, the production of a significantly higher mean static force compared with the dynamic force resulted in a significantly smaller BOLD signal in the contralateral motor cortex, confirming observations of an earlier investigation. In addition, we found that the ipsilateral anterior cerebellum behaved similar to the motor cortex, whereas in all other activated regions the activation during static and dynamic force did not significantly differ. These findings demonstrate that various regions of the sensorimotor network participate differentially in the production and control of low static and dynamic grip force, and raise important questions concerning the interpretation of the BOLD signal with respect to mechanisms of neurovascular coupling.