Dysphagia, or difficulty swallowing, is a devastating complication often following stroke—affecting up to 50% of acute stroke patients and increasing risks of aspiration pneumonia, malnutrition, and reduced quality of life (Smithard et al., 1998). Traditional rehabilitation approaches, such as compensatory head positions or muscle exercises, often lack strong evidence for efficacy (Speyer et al., 2010). However, recent advancements in neurostimulation have highlighted repetitive transcranial magnetic stimulation (rTMS) as a novel, non-invasive therapy for dysphagia. This blog explores the science behind rTMS, key research findings, and its potential to transform dysphagia care.

The Neurophysiology of Swallowing and rTMS Mechanisms

Swallowing is a complex motor function coordinated by a network of brain regions, including the cerebral cortex (primary sensorimotor cortex, insula), brainstem, and cerebellum (Michou et al., 2016). Following a stroke, focal brain lesions disrupt this network, but the brain’s neuroplasticity—its ability to reorganize neural pathways—offers a pathway to recovery.

rTMS leverages this plasticity by delivering magnetic pulses to targeted brain areas, modulating neuronal excitability. High-frequency rTMS (≥5 Hz) boosts cortical activity, while low-frequency stimulation (≤1 Hz) suppresses it (Maeda et al., 2000). For dysphagia, rTMS targets either the cerebral cortex (pharyngeal or mylohyoid motor areas) or the cerebellum— a region critical for planning complex motor tasks like swallowing (Jayasekeran et al., 2011; Sasegbon et al., 2020). By stimulating these areas, rTMS enhances excitability of swallowing-related neural pathways, promoting functional recovery (Michou et al., 2016).

Key Research Findings: rTMS for Dysphagia

Three landmark studies shed light on rTMS’s efficacy, particularly for post-stroke dysphagia, and compare stimulation strategies (unilateral vs. bilateral, cortical vs. cerebellar).

1. High-Frequency Cerebellar rTMS Improves Post-Brainstem Stroke Dysphagia

Dong et al. (2022) conducted a randomized controlled trial (RCT) with 34 patients with dysphagia after brainstem stroke, dividing them into three groups: bilateral cerebellar sham stimulation, unilateral dominant cerebellar rTMS + contralateral sham, and bilateral cerebellar rTMS. Stimulation parameters included 10 Hz frequency, 80% resting motor threshold (rMT), and 250 pulses per session.

After 2 weeks, both unilateral and bilateral rTMS groups showed significant improvements in two key clinical measures: the Penetration-Aspiration Scale (PAS) and Functional Dysphagia Scale (FDS) compared to the sham group. Notably, while bilateral stimulation increased motor evoked potential (MEP) amplitude—an indicator of neural excitability—more than unilateral stimulation, there was no significant difference in clinical swallowing outcomes between the two active groups (Dong et al., 2022). This suggests that even unilateral cerebellar rTMS can drive meaningful functional recovery, though bilateral stimulation may have stronger neurophysiological effects.

2. Bilateral Cerebellar rTMS Outperforms Unilateral Stimulation in Healthy Adults

In a cross-over study with 13 healthy participants, Sasegbon et al. (2020) compared unilateral and bilateral 10 Hz cerebellar rTMS. They measured pharyngeal motor evoked potential (PMEP) amplitude and swallowing accuracy, including after inducing a cortical “virtual lesion” (a temporary suppression of neural activity) to mimic stroke-related dysfunction.

Bilateral rTMS significantly increased PMEP amplitude compared to both baseline and unilateral stimulation, indicating greater enhancement of corticobulbar motor pathways to the pharynx. Additionally, bilateral stimulation was far more effective at reversing the suppressive effects of the virtual lesion—restoring both neural excitability and swallowing accuracy (Sasegbon et al., 2020). While this study focused on healthy individuals, it provides critical preclinical evidence that bilateral cerebellar rTMS may be a more potent therapeutic strategy for neurogenic dysphagia.

3. rTMS: A Promising but Heterogeneous Field

Michou et al. (2016) reviewed 10+ studies on rTMS for dysphagia, noting consistent trends but significant variability in protocols. Most RCTs demonstrated moderate improvements in swallowing function, with high-frequency rTMS (3–5 Hz) targeting the unaffected cerebral hemisphere or cerebellum showing particular promise. However, studies differed in key parameters: stimulation frequency (1–10 Hz), target area (pharyngeal, mylohyoid, or cerebellar), and patient populations (acute vs. chronic stroke, hemispheric vs. brainstem lesions) (Michou et al., 2016).

Notably, meta-analyses of these studies confirm rTMS’s overall efficacy but highlight the need for standardized protocols (Pisegna et al., 2015; Yang et al., 2015). For example, some studies used inhibitory low-frequency rTMS on the unaffected hemisphere to reduce transcallosal inhibition, while others used excitatory high-frequency stimulation on the lesioned side to boost local excitability (Michou et al., 2016). These differences make direct comparisons challenging but underscore rTMS’s flexibility as a therapy.

Clinical Implications and Future Directions

rTMS offers a non-invasive, targeted alternative to traditional dysphagia rehabilitation, with potential to accelerate recovery in stroke patients. Key takeaways for clinicians and researchers include:

• Cerebellar Targeting: Stimulating the cerebellum is a viable and effective strategy, as it modulates bilateral swallowing networks (Dong et al., 2022; Sasegbon et al., 2020).
• Bilateral vs. Unilateral: Bilateral stimulation may offer stronger neurophysiological benefits, but unilateral stimulation can still drive clinical improvements—making it a practical option for patients where bilateral targeting is impractical (Dong et al., 2022).
• Standardization: Future studies should align on core parameters (frequency, intensity, target area) and focus on large, multicenter RCTs to confirm efficacy across diverse patient populations (Michou et al., 2016).

References

1. Dong, L. H., Pan, X. N., Wang, Y. Y., et al. (2022). High-Frequency Cerebellar rTMS Improves the Swallowing Function of Patients with Dysphagia after Brainstem Stroke. Neural Plasticity, 2022, 6259693. https://doi.org/10.1155/2022/6259693
2. Jayasekeran, V., Rothwell, J., & Hamdy, S. (2011). Non-invasive magnetic stimulation of the human cerebellum facilitates cortico-bulbar projections in the swallowing motor system. Neurogastroenterology and Motility, 23(9), 831–e341. https://doi.org/10.1111/j.1365-2982.2011.01747.x
3. Maeda, F., Keenan, J. P., Tormos, J. M., et al. (2000). Modulation of corticospinal excitability by repetitive transcranial magnetic stimulation. Clinical Neurophysiology, 111(5), 800–805. https://doi.org/10.1016/S1388-2457(99)00323-5
4. Michou, E., Raginis-Zborowska, A., Watanabe, M., et al. (2016). Repetitive Transcranial Magnetic Stimulation: a Novel Approach for Treating Oropharyngeal Dysphagia. Current Gastroenterology Reports, 18(10), 1–12. https://doi.org/10.1007/s11894-015-0483-8
5. Pisegna, J. M., Kaneoka, A., Pearson, W. G., Jr., et al. (2015). Effects of non-invasive brain stimulation on post-stroke dysphagia: A systematic review and meta-analysis of randomized controlled trials. Clinical Neurophysiology. https://doi.org/10.1016/j.clinph.2015.05.015
6. Sasegbon, A., Smith, C. J., Bath, P., et al. (2020). The effects of unilateral and bilateral cerebellar rTMS on human pharyngeal motor cortical activity and swallowing behavior. Experimental Brain Research, 238(7–8), 1719–1733. https://doi.org/10.1007/s00221-020-05787-x
7. Smithard, D. G., O’Neill, P. A., Parks, C. G., & Morris, J. K. (1998). Complications and outcome after acute stroke. Does dysphagia matter? Stroke, 29(7), 1200–1204. https://doi.org/10.1161/01.STR.29.7.1200
8. Speyer, R., Baijens, L. W., Heijnen, M. J., et al. (2010). Effects of therapy in oropharyngeal dysphagia by speech and language therapists: a systematic review. Dysphagia, 25(1), 40–65. https://doi.org/10.1007/s00455-009-9239-7
9. Yang, S. N., Pyun, S. B., Kim, H. J., et al. (2015). Effectiveness of Non-invasive Brain Stimulation in Dysphagia Subsequent to Stroke: A Systematic Review and Meta-analysis. Dysphagia, 30(4), 383–391. https://doi.org/10.1007/s00455-015-9619-0