The precision grip task and parametric modulation.

(A) The tonic precision grip task consisted of 12 task blocks (each 20 s) alternated by periods of rest (20 s). During the grip task, visual feedback of the exerted grip force (blue area) and the required target force (grey circle) was continuously provided. (B) Participants had to maintain a target force corresponding to 20% of the individual maximal voluntary contraction and the grip force output was continuously recorded. (C) Task-related activity was analysed using a General Linear Model in which the constant main effect of task (main effect) as well as linear modulation of task-related activity (linear time effect) were modelled. Task-related activation during the first block (red line) was separately modelled and treated as effect of no interest.