fMRI in Bell's Palsy: Cortical Activation is Associated with Clinical Status in the Acute and Recovery Phases

Neural mechanisms of acupuncture for peripheral facial nerve palsy: A protocol for systematic review and meta analysis

BACKGROUND

Peripheral facial nerve palsy (PFNP) is a cranial neuropathy that occurs when the seventh facial nerve is damaged. PFNP seriously affects patients' quality of life, and approximately 30% of patients suffer from sequelae, such as unrecovered palsy, synkinesis, facial muscle contracture, and facial spasm. Many studies have confirmed the effectiveness of acupuncture for the treatment of PFNP. However, the specific mechanism remains unclear and needs to be further explored. Therefore, the purpose of this systematic review is to investigate the neural mechanisms underlying acupuncture treatment for PFNP using neuroimaging methods.

METHODS

We will search all published studies from inception to March 2023 using the following databases: MEDLINE, Cochrane Library, EMBASE, CNKI, KMBASE, KISS, ScienceON, and OASIS. All clinical studies evaluating the effectiveness of acupuncture for treating PFNP using functional neuroimaging will be selected without language restrictions. Two reviewers will independently conduct the study selection, data extraction, and risk of bias assessment, according to a predetermined protocol. The outcomes, including the types of functional neuroimaging techniques, brain function alterations, and clinical outcomes, such as the House-Brackmann scale and Sunnybrook Facial Grading System, will also be analyzed. Coordinate-based meta-analysis and subgroup analyses will be performed if possible.

RESULTS

This study will analyze the effect of acupuncture on brain activity alterations and clinical improvement in patients with PFNP using functional neuroimaging.

CONCLUSION

This study will provide a comprehensive summary and help elucidate the neural mechanisms of acupuncture treatment for PFNP.

PROSPERO REGISTRATION NUMBER

CRD42022321827.

Exploratory Study of the Brain Response in Facial Synkinesis after Bell Palsy with Systematic Review and Meta-analysis of the Literature

BACKGROUND

Facial synkinesis, characterized by unintentional facial movements paired with intentional movements, is a debilitating sequela of Bell palsy.

PURPOSE

Our aim was to determine whether persistent peripheral nerve changes arising from Bell palsy result in persistent altered brain function in motor pathways in synkinesis.

DATA SOURCES

A literature search using terms related to facial paralysis, Bell palsy, synkinesis, and fMRI through May 2021 was conducted in MEDLINE and EMBASE. Additionally, an fMRI study examined lip and eyeblink movements in 2 groups: individuals who fully recovered following Bell palsy and individuals who developed synkinesis.

STUDY SELECTION

Task-based data of the whole brain that required lip movements in healthy controls were extracted from 7 publications. Three studies contributed similar whole-brain analyses in acute Bell palsy.

DATA ANALYSIS

The meta-analysis of fMRI in healthy control and Bell palsy groups determined common clusters of activation within each group using activation likelihood estimates. A separate fMRI study used multivariate general linear modeling to identify changes associated with synkinesis in smiling and blinking tasks.

DATA SYNTHESIS

A region of the precentral gyrus contralateral to the paretic side of the face was hypoactive in synkinesis during lip movements compared with controls. This region was centered in a cluster of activation identified in the meta-analysis of the healthy controls but absent from individuals with Bell palsy.

LIMITATIONS

The meta-analysis relied on a small set of studies. The small sample of subjects with synkinesis limited the power of the fMRI analysis.

CONCLUSIONS

Premotor pathways show persistent functional changes in synkinesis first identifiable in acute Bell palsy.

Identifying Modulated Functional Connectivity in Corresponding Cerebral Networks in Facial Nerve Lesions Patients With Facial Asymmetry

Facial asymmetry is the major complaint of patients with unilateral facial nerve lesions. Frustratingly, although patients experience the same etiology, the extent of oral commissure asymmetry is highly heterogeneous. Emerging evidence indicates that cerebral plasticity has a large impact on clinical severity by promoting or impeding the progressive adaption of brain function. However, the precise link between cerebral plasticity and oral asymmetry has not yet been identified. In the present study, we performed functional magnetic resonance imaging on patients with unilateral facial nerve transections to acquire in vivo neural activity. We then identified the regions of interest corresponding to oral movement control using a smiling motor paradigm. Next, we established three local networks: the ipsilesional (left) intrahemispheric, contralesional (right) intrahemispheric, and interhemispheric networks. The functional connectivity of each pair of nodes within each network was then calculated. After thresholding for sparsity, we analyzed the mean intensity of each network connection between patients and controls by averaging the functional connectivity. For the objective assessment of facial deflection, oral asymmetry was calculated using FACEgram software. There was decreased connectivity in the contralesional network but increased connectivity in the ipsilesional and interhemispheric networks in patients with facial nerve lesions. In addition, connectivity in the ipsilesional network was significantly correlated with the extent of oral asymmetry. Our results suggest that motor deafferentation of unilateral facial nerve leads to the upregulated ipsilesional hemispheric connections, and results in positive interhemispheric inhibition effects to the contralesional hemisphere. Our findings provide preliminary information about the possible cortical etiology of facial asymmetry, and deliver valuable clues regarding spatial information, which will likely be useful for the development of therapeutic interventions.

Central functional reorganization and recovery following facial-hypoglossal neurorrhaphy for facial paralysis

OBJECTIVE

Functional deficits induced by nerve injuries can be restored by achieving effective reinnervation of the denervated targets and functional reorganization of the central nervous system after nerve reconstruction. In this study, we investigated the effect and extent of cortical functional reorganization related to the ability of transferred hypoglossal neurons to restore facial function in facial paralysis patients after a surgical bridge of neurorrhaphy ectopically between the ipsilateral hypoglossal nerve and injured facial nerve.

METHODS

We treated 23 patients (35.4 ± 10.3 years, 10 males) and followed them up for 2.9 ± 0.61 years. We used motor-task-related functional magnetic resonance imaging to map activation change at multiple time points before and after neurorrhaphy; 20 normal subjects were included as control.

RESULTS

All patients regained facial function to some extent after neurorrhaphy. Enhanced activation in motor-related cortices gradually returned to normal levels and was positively correlated with regained facial function. The related cortical functional areas included the left middle temporal gyrus, left inferior frontal gyrus, insula, bilateral motor cortex and the supplementary motor area extending to the paracingulate involved in intensive eye closing, as well as the left superior temporal gyrus, right putamen and the bilateral motor cortex involved in lip pursing. Intriguingly, significant correlations were found between the pre-surgery activation while intensive eye closing in bilateral motor cortex and recovery of facial nerve function induced by the neurorrhaphy treatment.

CONCLUSION

This is the first study mapping activation change in motor cortices at multiple time points before and after repair of the facial nerve. The cortex functional reorganization found may suggest potential treatment targets in the central nervous system for adjuvant therapies such as repetitive transcranial magnetic stimulation to further improve functional recovery.