Reduced functional connectivity within the primary motor cortex of patients with brachial plexus injury

• Patients with brachial plexus avulsion were evaluated employing resting state fMRI.
• Faster correlation decay between voxels was found in BPA compared to controls in M1.
• No difference between groups was found in M1 face area.
• No gray matter diminution was observed in M1 in BPA compared to controls.
• This decay could result from reduced activity in intrinsic horizontal connections.

This study aims at the effects of traumatic brachial plexus lesion with root avulsions (BPA) upon the organization of the primary motor cortex (M1). Nine right-handed patients with a right BPA in whom an intercostal to musculocutaneous (ICN-MC) nerve transfer was performed had post-operative resting state fMRI scanning. The analysis of empirical functional correlations between neighboring voxels revealed faster correlation decay as a function of distance in the M1 region corresponding to the arm in BPA patients as compared to the control group. No differences between the two groups were found in the face area. We also investigated whether such larger decay in patients could be attributed to a gray matter diminution in M1. Structural imaging analysis showed no difference in gray matter density between groups. Our findings suggest that the faster decay in neighboring functional correlations without significant gray matter diminution in BPA patients could be related to a reduced activity in intrinsic horizontal connections in M1 responsible for upper limb motor synergies.