Article Information

<table><tr><td>Article Type:</td><td>research-article</td></tr><tr><td>Journal Title:</td><td>Facial Plastic Surgery & Aesthetic Medicine</td></tr><tr><td>Publisher:</td><td>Mary Ann Liebert, Inc., publishers</td></tr><tr><td>ISSN (P):</td><td>2689-3614</td></tr><tr><td>ISSN (E):</td><td>2689-3622</td></tr><tr><td>DOI Number:</td><td>10.1089/fpsam.2023.0235</td></tr><tr><td>Volume Number:</td><td>00</td></tr><tr><td>Issue Number:</td><td>00</td></tr><tr><td>First Page:</td><td>000</td></tr><tr><td>Last Page:</td><td>000</td></tr><tr><td>Copyright:</td><td>Copyright 2024, Mary Ann Liebert, Inc., publishers</td></tr><tr><td></td><td>↑</td></tr></table>
# Cerebral Plasticity after Lengthening Temporalis Myoplasty in Facial Palsy: A Magnetoencephalography Study

**Left running head:** HERVOCHON ET AL.

**Short title:** CEREBRAL PLASTICITY AFTER LTM WITH MEG

Rémi Hervochon, MD, MSc,<sup>1,2,3,*</sup> Maximilien Chaumon, PhD,<sup>1,3</sup> Deborah Ziri, PhD,<sup>1</sup> Claire Foirest, MD, MSc,<sup>1,2,3</sup> Denis Schwartz, PhD,<sup>1,3</sup> Nathalie George, PhD,<sup>1,3</sup> Frédéric Tankere, MD, PhD<sup>1,2,3</sup> and †

## Footnotes

†Co-last authors.

## Corresponding Author

*Address correspondence to: Rémi Hervochon, MD, MSc, Service d'ORL et Chirurgie Cervico-Faciale, Groupe Hospitalier Pitié-Salpêtrière, 47-83 Boulevard de l'Hôpital 75013 Paris France, remihervochon@gmail.com

<sup>1</sup>ORCID ID (https://orcid.org/0000-0003-1569-3578).

## Introduction

Orthodromic temporalis tendon transfer, also called lengthening temporalis myoplasty (LTM), a surgery performed on patients with facial palsy, involves suturing the temporal muscle to the peribuccal region.<sup>1,2</sup> It allows a reanimated smile by contracting a muscle whose initial function is mastication. This suggests cerebral plasticity.

<footnote n="1"><sup>1</sup>Sorbonne Université, Institut du Cerveau-Paris Brain Institute-ICM, Inserm, CNRS, APHP, Hôpital de la Pitié Salpêtrière, Paris, France.</footnote>

<footnote n="2"><sup>2</sup>AP-HP, Hôpital de la Pitié Salpêtrière, Oto-Rhino-Laryngology and Cervico-Facial Surgery Department, Paris, France.</footnote>

<footnote n="3"><sup>3</sup>Institut du Cerveau, ICM, Inserm U 1127, CNRS UMR 7225, Sorbonne Université, CENIR, Centre MEG-EEG, Paris, France.</footnote>
Magnetoencephalography (MEG) is a functional brain imaging method allowing noninvasive detection of magnetic fields produced by electrical activity of neuronal ensembles. ³

We performed a pilot study with MEG to map the somatotopy of the face in controls and in patients after LTM, during motor tasks. Our main objective was to obtain preliminary evidence for the face motor cortex reorganization after LTM, which is still unclear.⁴

Materials and Methods

Eleven controls and 8 patients who underwent LTM and physiotherapy were included. The Ethics Committee approved the study. Participants underwent anatomical MRI and MEG at Paris Brain Institute.

Neuromagnetic fields were recorded with a 306-channel whole-head Elekta Neuromag® Triux MEG system.

Electromyograms were recorded with electrodes placed on the skin above the following muscles: temporalis, orbicularis oculi, zygomaticus, genioglossus, and flexor pollicis brevis.

Participants performed five motor tasks with magnetoencephalography and electromyographic recordings: "thumb flexion," "eye closure," "smile without biting," "tongue protraction," and "mastication."

We localized the maximal source within the precentral gyrus (Fig. 1) and measured the L distance between this point and the vertex. [AQ1]
<figure><img src="image_1.png" /><figcaption>Fig. 1. Maximum source intensity points within the left precentral gyrus projected on the MNI template for the five tasks. The 11 controls are shown in green and the 6 LTM patients operated on the right side are shown in pink. **A:** Thumb, **B:** Eye, **C:** Smile, **D:** Tongue, and **E:** Mastication.</figcaption></figure>

We performed an ANOVA to test for differences in the source localization of the 5 tasks. We performed between-group comparisons for each task, and between-task comparisons within each group. A Student's t-test and a two one-sided test (TOST) were performed on L distance between tasks.

We used a somatotopy index (SI).⁵ It is equal to 1 in the case where cerebral sources are found in the exact normal order, or different from 1, in other cases.

## Results

ANOVA revealed a marked effect of the task [$F(4,68) = 53.82, p < 2.10^{-16}$] and no significant main effect of the group [$F(1,17) = 1.15, p = 0.30$]. The interaction between group and task was statistically significant [$F(4,68) = 3.26, p = 0.017$].

For Smile and Mastication, there was a statistically significant difference in CTRL ($p = 0.00016$), but no such difference was observed in LTM ($p = 0.9996$). For Smile and Mastication, the equivalence test (TOST) was nonsignificant in LTM [$t(7) = 0.933, p = 0.191$] with a boundary for equivalence set at 10% (7.5 mm).

In the CTRL group, 81.8% had a SI = 1. In the LTM group, 25.0% had a SI = 1 ($p = 0.024$).
Discussion

In controls, the cortical motor areas were organized according to Penfield's motor homunculus. After LTM, the organization was different: smile and mastication sources were found to be not statistically different and seem to overlap (Fig. 2).

<figure><img src="image_2.png" /><figcaption>Fig. 2. Distance L for each subject and each motor task. Each point is one subject in a given task. Standard box plots are used. The horizontal line in the box represents the median. [AQ3]</figcaption></figure>

Cerebral plasticity is the capacity of the brain to modify its functional organization after pathological transformations, learning, or modification of body structures.

One study investigated cerebral plasticity after LTM,⁴ using fMRI: they showed an enlargement of the smile area, merging with the mastication one. Buendia showed similar brain activity for smile and mastication in facial palsy patients rehabilitated by a transfer of the masseteric nerve, whose initial function is masticatory.⁶

Our findings should be considered as preliminary, since the small sample size of our study limits their generalizability. As a consequence, the size of the effects reported in this study should be considered with
caution. Another limitation is the absence of preoperative data, raising the possibility that the changes that we observed were not solely due to LTM. We are leading further research with larger sample size and longitudinal data to fully characterize the brain plasticity. It is noteworthy that we could not make right-left comparisons, since the cerebral MEG signal on the operated side was too artifactual because of the metal fixations on the zygomatic arch.

## Acknowledgments

**Jonathan Barbut:** conceptualization. **Christophe Gitton:** methodology and software.

## Authors' Contributions

Conceptualization: F.T., N.G., R.H., and D.S. Data curation: R.H., M.C., D.Z., C.F., and D.S. Formal Analysis: M.C., N.G., R.H., D.Z., and C.F. Methodology: F.T., N.G., R.H., and D.S. Software: M.C. and D.S. Supervision: N.G., F.T., and D.S. Writing—original draft: R.H., M.C., D.Z., C.F., D.S., N.G., and F.T. Writing—review & editing: R.H., M.C., D.Z., C.F., D.S., N.G., and F.T.

## Author Disclosure Statement

No competing financial interests exist.

## Funding Information

This research has received funding from the “Fondation pour la Recherche Médicale” and from “Fondation des Gueules Cassées” and was performed on a platform of France Life Imaging network partly funded by the grant “ANR-11-INBS-0006” and by the program “Investissements d’avenir” ANR-10-IAIHU-06. The funding bodies had no role in the study design, the data collection, analysis or interpretation, or the article writing. Authors have no commercial associations or financial disclosures.

## References

1. Patel NN, Zebolsky AL, Park AM, et al. Smile outcomes of an externally scarless, intraoral orthodromic temporalis tendon transfer. *Facial Plast Surg Aesthet Med.* 2022;24(2):83–88; doi: 10.1089/fpsam.2021.0028

<figure><img src="image_3.png" /></figure>

2. Labbe DMD, Huault MMD. Lengthening temporalis myoplasty and lip reanimation. *Plastic & Reconstructive Surgery.* 2000;105(4):1289–1297.

<figure><img src="image_4.png" /></figure>

3. Yang TT, Gallen CC, Schwartz BJ, et al. Noninvasive somatosensory homunculus mapping in humans by using a large-array biomagnetometer. *Proc Natl Acad Sci U S A.* 1993;90(7):3098–3102.

<figure><img src="image_5.png" /></figure>
4. Garmi R, Labbé D, Coskun O, et al. Lengthening temporalis myoplasty and brain plasticity: A functional magnetic resonance imaging study. *Ann Chir Plast Esthet*. 2013;58(4):271-276; doi: 10.1016/j.anplas.2013.03.002

<figure><img src="image_6.png" /></figure>

5. Meunier S, Garnero L, Ducorps A, et al. Human brain mapping in dystonia reveals both endophenotypic traits and adaptive reorganization. *Ann Neurol*. 2001;50(4):521-527.

<figure><img src="image_7.png" /></figure>

6. Buendia J, Loayza FR, Luis EO, et al. Functional and anatomical basis for brain plasticity in facial palsy rehabilitation using the masseteric nerve. *J Plast Reconstr Aesthet Surg*. 2016;69(3):417-426; doi: 10.1016/j.bjps.2015.10.033

<figure><img src="image_8.png" /></figure>
Author Query

1. **Query** [AQ1] : "L distance" has been mentioned twice in the article but its definition not provided. Please check.

<figure><img src="image_9.png" /></figure>

Response by Author: "Ok"

2. **Query** [AQ2] : Please check whether the Acknowledgments statement has been set correctly. Amend if necessary.

<figure><img src="image_10.png" /></figure>

Response by Author: "Ok"

3. **Query** [AQ3] : The figure 2 appear to be blurry and have a low resolution. Please provide high quality figures with a minimum resolution of 300 dpi.

<figure><img src="image_11.png" /></figure>

Response by Author: "Ok"