fMRI characterization of intrinsic brain networks relevant for motor control with and without visual feedback by fractal dimension

The bilateral visuo-parietal-motor network is responsible for fine control of hand movements. However, the subregions devoted to maintaining contraction stability in the presence/absence of visual feedback remain unclear. It is widely recognized that continuous sensory feedback plays a crucial role in accurate motor control in everyday life. Feedback information is used to adapt force output and to correct errors. While the primary motor cortex contralateral to the movement (cM1) plays a dominant role in this control, converging evidence supports the idea that the ipsilateral primary motor cortex (iM1) also directly contributes to hand and finger movements. Similarly, when visual feedback is available, the primary visual cortex (V1) and the visuospatial network and their interactions with the motor network are essential for accurate motor performance. To clarify this problem and investigate the regions involved in a visuomotor task, we performed functional magnetic resonance imaging (fMRI) measurements during isometric compression of a compliant rubber bulb, at 10% of maximum voluntary contraction, both with (visuomotor task) and without visual feedback (motor task). Here, by using a multivariate approach focusing on intrinsic connectivity between voxels through group ICA of fMRI Toolbox (GIFT), we have answered the following two main questions: 1) which are the networks involved during a motor task (i.e. without visual feedback) and a visuomotor task (i.e. with visual feedback)? 2) Is there any hemodynamic signal complexity difference between the visuomotor and the motor task? Interestingly, we have found that during the visuomotor task, the involvement of the visuospatial network (FEF), the ipsilateral primary motor area (iM1), the contralateral primary motor area (cM1), the sensorimotor network (SMN) the Executive Control Network (ExCN), the Silence Network (SN), the Default Mode Network (DMN), the Basal Ganglia (BG), the Cerebellum (Cb) and Precuneus are essential for the fine motor control of the movement while maintaining the grip force level indicated by the visual feedback together with higher complexity estimated by Higuchi's Fractal Dimension. The study shows that the brain networks show greater hemodynamic complexity in the presence of visual feedback, due to the processing of the visual stimulus and the maintenance of the required level of force.