Anticipatory effects of multi-step action: a fMRI study

The way we grasp objects (e.g., over- vs. under-hand) depends on sensory information concerning the state of the body (e.g., posture) and the target object (e.g., location, orientation, form), as well as prediction of forthcoming task demands (e.g., intended rotation of the target object). This ability to predict the consequences of our own multi-step actions relies on the use of internal models and reflects the temporally-extended nature of internal action representations (Johnson-Frey et al., 2004). Previous work showed that a parieto-frontal circuit is involved in the transformation of sensory information into a motor plan for grasping (Johnson et al., 2002). Are these same circuits involved in grip selection decisions influenced by predicted demands of a forthcoming object rotation? Event-related fMRI was used to ask this question in 15 healthy, right-handed adults. Participants were asked to select the most comfortable way (over- vs. underhand) to grasp a handle using either hand with the intention of rotating it in a cued direction or to only grasp the handle. Even if movement execution was not required, grip preferences were significantly affected by the predicted demands of handle rotation. Preparation for an imagined anticipatory grip selection activates the same parieto-frontal networks involved in both the rotation and no-rotation conditions. Specifically, brain regions involved are bilateral dorsal premotor cortex (dPMC), bilateral intraparietal sulcus (IPS) and cerebellum. Further, fMRI data suggest that prediction of these demands is accomplished in the very same neural structures as grip selection based on available sensory information.