fMRI effects of task demand and feedback accuracy on grip force tracking.

Previous research showed that force control in a visually guided continuous tracking task is influenced by feedback accuracy and force-varying rate. More specifically it was found that higher feedback accuracy and greater force-varying rate led to decreased task performance. Here we studied the neural signature of these effects using functional MRI. We hypothesised that performance costs were due to increased task demand and reflected by increased activations in the visuomotor network. Using the fMRI-BOLD response as an indirect measure of enhanced brain activity we found that the task induced activations in the visuomotor network. The different task conditions thereby modulated the BOLD response such that those conditions with poorest performance showed highest activation levels and vice versa. This indicates a parametric modulation of the BOLD response according to task difficulty and force production. The effects point towards the interdependent and parallel control of visual feedback information and force output rate, which is probably achieved through a joint neural network.