Related timing for peripheral and central plasticity in hypoglossal-facial nerve anastomosis

The aim of this work was to determine the role of peripheral facial muscle reinnervation in the central reorganization of the blink reflex (BR) after hypoglossal-facial anastomosis (HFA). An electrophysiological study was performed on seven patients who underwent HFA after facial nerve transection during surgery for acoustic neuroma. HFA was performed within 15 days after surgery in five patients (group 1) and later for the two others (group 2). We studied the motor responses (MR) and the BR evoked on the affected side, before and over 3 years after the HFA. The MR appeared by the third month for the first group, and by the sixth and twelfth for the second group. After 36 months, the amplitude of MR was significantly higher than its control value, showing hyperinnervation of the facial muscles. Study of the BR evoked only an R1-type blink response that was observed 4 and 6 months after the MR for groups 1 and 2, respectively. This central reorganization appeared closely correlated with muscle reinnervation and its related timing. The occurrence of peripheral nerve-muscle contacts seems to be a necessary condition for reorganization of the trigemino-hypoglossal-facial reflex.