Transition from rest to movement: brain correlates revealed by functional connectivity.

It is suggested that resting state networks reflecting correlated neural regional activities participate significantly in brain functioning. A fundamental issue is to understand how these networks interact and how their activities change during behavioral transitions. Our aim was to understand better with functional MRI connectivity how the brain switched from a "resting" to a movement-related state by exploring the transitory readiness state for an intended movement of the right hand. Our study does not address movement preparation occurring in a time scale of milliseconds before movement which has been widely studied but movement-readiness which can last longer. At rest, in the absence of overt goal-directed behavior, a "default-mode" network, whose main areas are the posterior cingulate cortex and precuneus (PCC/Pcu), shows high activity interpreted as day dreaming, free association, stream of consciousness, and inner rehearsal. We found that, during rest, the "default-mode" network and the sensorimotor network were not functionally correlated. During movement-readiness, the two networks were functionally correlated through an interaction between the PCC/Pcu and the medial superior parietal cortex in the upper precuneus. The complex PCC/Pcu has been shown to be involved in retrieval and/or setting up spatial attributes for motor imagery, and thus, would be a key region in the movement-readiness phase. It might functionally connect to the medial superior parietal cortex to initiate the movement programming through retrieval of suited movement parameters. The anterior cingulum, functionally correlated to the primary sensorimotor cortex during movement-readiness would have a motivational role or could generate predictions about the movement.