Neuroplastic Reorganisation with Brachial Plexus Lesions

After severe traumatic injuries, avulsions of nerve roots from the cervical spinal cord may happen. This results in a complete palsy of the arm (complete brachial plexus palsy) - one of the most serious motor disabilities for humans. Reconstitution of arm functions is a major neurological and surgical problem. Since recently, clinical data of a new surgical approach show promising rehabilitation results. This technique connects the ending of the disrupted "elbow flexion nerve" (musculocutaneous nerve) with the side of the intact "diaphragm nerve" (phrenic nerve). Over several months, the nervous system learns to control breathing and elbow flexion independently via the phrenic nerve. Currently it is not clear, which reorganisation processes are responsible for the observed clinical success and how such processes could be optimized. The goal of this grant application is to clarify and understand the reorganisation processes of the central nervous system which lead to successful rehabilitation. This shall be done by performing comprehensive clinical and functional imaging investigations (functional magnetic resonance imaging at 3 Tesla and 7 Tesla) in affected patients. Based on own pilot studies, the applicants expect a description of hitherto unknown capabilities for reorganisation of the nervous system and deduction of consequences for new therapeutic procedures.

The primary goal of the study was to clarify which capabilities for reorganization exist within the human brain after suffering from injury of the peripheral nervous system. For this a group of rare patients with a very specific peripheral nervous system damage was investigated clinically and with functional magnetic resonance imaging. The patients suffered from a traumatic avulsion of the nerves for the arm (arm plexus) in the spine and shoulder area with the consequence of a complete arm paresis. In these patients a reconnection of the nerve responsible for arm flexion with the nerve responsible for diaphragma breathing was performed in an end-to-side fashion (end of arm nerve connected to side of diaphragma nerve). As a consequence the diaphragma nerve can now control 2 muscles: the diaphragma and the biceps for elbow flexion and the brain has to learn to activate both muscles independently. It takes about 1-2 years until the human brain is reorganized in a fashion that the same brain area (the diaphragma area) can now independently activate the diaphragma and the arm. It is important to note that this reorganization takes place within a healthy human brain and has to be separated from forced reorganizations due to brain damage (as well known after a stroke). This project was able to document this new type of brain reorganization for the first time. It was also possible to clarify the astonishing mechanism, how the brain changes to achieve this. When deconnecting the brains arm area (nerve cells for arm movements) from the arm muscles, one would expect that the arm area is abandoned and the newly connected diaphragma area (now connected to the arm muscles) would take over. However, this does not happen: the arm area still activates with intended arm movements and connects with the diaphragm area to transfer the movement commands to the arm muscles. This new type of functional connectivity bears the potential for new clinical applications.