The Laryngoscope Lippincott Williams & Wilkins © 2008 The American Laryngological, Rhinological and Otological Society, Inc. Functional Assessments of the Rodent Facial Nerve: A Synkinesis Model Tessa Hadlock, MD; Jeffrey Kowaleski, BS; David Lo, BS; Roberto Bermejo, PhD; H. Philip Zeigler, PhD; Susan Mackinnon, MD; James T. Heaton, PhD Objectives/Hypothesis: Rodent whisker move- ment has been used as a tool, after facial nerve manipu- lation, to quantify functional recovery. We have recently established a method to study functional correlates of aberrant regeneration of the facial nerve. Our objective was to establish normative parameters for both sponta- neous and induced whisking and blinking behavior in a large group of normal rats. Study Design: Prospective animal study. Methods: Eighty animals underwent quantitative facial movement testing to measure simultaneous vibris- sal movement and ocular closure for each side indepen- dently. Right and left C-1 whisker positions were contin- uously recorded for 5-minute sessions, and changes in infrared detection corresponding to eye closure were con- tinuously recorded. Whisking and blinking were elicited by delivery of olfactory stimuli (10 s scented airflows) and corneal air puffs. Whisks were counted and analyzed, and eye closures were counted. Results: Whisking amplitude, velocity, and acceler- ation were consistent with literature values. Air puff de- livery elicited an ipsilateral blink 99% of the time, a contralateral blink 18% of the time, and changes in or initiation of bilateral whisking 70% of the time. Olfactory stimulus delivery prompted a change in whisking behav- ior 83% of the time, and eye closure 20% of the time. Conclusions: This study establishes normative data for assessing cranial nerve VII-controlled facial movement in four separate facial regions. We demonstrate the capability and tendency of animals to move their orbicularis oculi muscles independently of and simulta- neously with their midfacial muscles. This model pro- vides an excellent tool for the study of aberrant regen- eration after facial nerve injury in the rodent. Key Words: Rodent facial nerve, synkinesis, whisk- ing, kinematics. Laryngoscope, 118:1744 –1749, 2008 INTRODUCTION After facial nerve injury, patients face two dominant clinical problems. The first is inadequate recovery of func- tion of the facial musculature, with weak or incomplete eye closure, and/or a weak smile on the affected side. The second problem is aberrant regeneration, where axons reach different muscle targets than their original targets during the recovery process, and is extremely common among those facing delayed recovery after facial nerve in- sult. This phenomenon, termed synkinesis, results in the involuntary movement of one segment of the face during attempts at voluntary movement of another. Extensive in- vestigative effort has been focused on the former issue (weakness), and progress toward improved overall axonal traversing of nerve grafts has been steady. The beneficial role of Schwann cells, graft architecture, and different growth promoting substances in the regenerating milieu has been established, and research approaches that com- bine favorable biological and physical elements in an ideal neural regeneration conduit seem promising (for review, see Ref. 1). With emerging technologies that permit time- lapse observations of motor nerve axonal extension and branching during regeneration, our understanding of the factors that underlie regeneration has deepened. 2–6 The latter problem, of axonal misrouting, has been investigated far less thoroughly, with only a few labora- tories concentrating on synkinesis after facial nerve in- jury, and strategies to control it. 7–13 To date, no medical therapy exists to prevent or diminish the emergence of synkinesis, despite the fact that patients at high risk for its development are easy to identify. Because a clinical window nearly always exists between identifying patients as “likely to develop synkinesis,” and the actual onset of From the Department of Otology and Laryngology (T.H., J.K., D.L.), Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts, U.S.A.; Biopsychology Program (R.B., H.P.Z.), Hunter Col- lege, City University of New York, New York, New York, U.S.A.; Division of Plastic and Reconstructive Surgery, Department of Surgery (S.M.), Wash- ington University, St. Louis, Missouri, U.S.A; and Department of Surgery (J.T.H.), Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, U.S.A. Editor’s Note: This Manuscript was accepted for publication May 8, 2008. Presented at the American Society for Peripheral Nerve Meetings, Beverly Hills, California, U.S.A., January 9, 2008. Supported by NIDCR K-08 DE015665-01A2. Send correspondence to Tessa Hadlock, MD, Department of Otolar- yngology–Head and Neck Surgery, Massachusetts Eye and Ear Infirmary, Boston, MA 02114. E-mail: tessa_hadlock@meei.harvard.edu DOI: 10.1097/MLG.0b013e31817f5255 Laryngoscope 118: October 2008 Hadlock et al.: Normative Rodent Facial Function 1744