Motor Readiness Increases Brain Connectivity Between Default-Mode Network and Motor Cortex: Impact on Sampling Resting Periods from fMRI Event-Related Studies

Abstract

The default-mode network (DMN) has been implicated in many conditions. One particular function relates to its role in motor preparation. However, the possibly complex relationship between DMN activity and motor preparation has not been fully explored. Dynamic interactions between default mode and motor networks may compromise the ability to evaluate intrinsic connectivity using resting period data extracted from task-based experiments. In this study, we investigated alterations in connectivity between the DMN and the motor network that are associated with motor readiness during the intervals between motor task trials. fMRI data from 20 normal subjects were acquired under three conditions: pure resting state; resting state interleaved with brief, cued right-hand movements at constant intervals (lower readiness); and resting state interleaved with the same movements at unpredictable intervals (higher readiness). The functional connectivity between regions of motor and DMNs was assessed separately for movement periods and intertask intervals. We found a negative relationship between the DMN and the left sensorimotor cortex during the task periods for both motor conditions. Furthermore, during the intertask intervals of the unpredictable condition, the DMN showed a positive relationship with right sensorimotor cortex and a negative relation with the left sensorimotor cortex. These findings indicate a specific modulation on motor processing according to the state of motor readiness. Therefore, connectivity studies using task-based fMRI to probe DMN should consider the influence of motor system modulation when interpreting the results.

Keywords: connectivity; default-mode network; fMRI; motor network; movement preparation; resting state.