Cerebral plasticity after hypoglosso-facial anastomosis in facial palsy: a magnetoencephalography study

Hypoglosso-facial anastomosis (HFA) consists in suturing the proximal part of the hypoglossal nerve with the distal part of the facial nerve in patients with facial palsy. Axonal regrowth through the anastomosis makes it possible to restore facial motor skills, which become spontaneous after physiotherapy. This suggests cerebral plasticity.

We used magnetoencephalography (MEG) in a pilot study to test this hypothesis.

Twenty-one healthy volunteers (CTRL) and 12 patients after HFA performed 5 motor tasks with MEG and electromyographic recordings: eyelid closure, smile, tongue protraction, mastication and thumb flexion. For each task, we picked the location of the maximum source activity within the precentral gyrus. We calculated the distances between this location and the vertex for each task and a somatotopy index.

There was an interaction between the participant's group and the task (F(4,124) = 4.07, p = 0.0039). In CTRL, the maximum source location was statistically different between smile and tongue tasks and between eyelid and tongue tasks (p < 0.001). No such difference was observed in HFA (p = 1.000). 90.5 % of CTRL and 41.7 % of HFA showed a normal somatotopy (p = 0.0046).

In CTRL, the organization of the cortical motor areas was similar to that of Penfield's motor Homunculus. In contrast, in HFA, eyelid closure, tongue protraction and smile areas were not significantly distinct. This supports the hypothesis of cerebral plasticity after HFA.The Ethical Committee of Paris Idf VI approved the study (CPP Ouest 6-CPP975-HPS2).