Background: Lengthening temporalis myoplasty (LTM) is a technique developed since ten years for facial paralysis. A spontaneous smile is acquired after this surgery explains by brain plasticity and the aim of the study is to confirm this plasticity by functional magnetic resonance imaging. Materials and Methods: A functional magnetic resonance imaging (fMRI) was performed at various time points in ten patients who were operated on LTM during one year. Results: Two different areas were found to be involved in chewing and smiling. We observed changes in the areas involved in smiling and chewing three months after surgery, and these changes persisted for at least one year. Conclusions: Our findings thus confirm that brain plasticity underlies the clinical observation of acquisition of a spontaneous smile.