TMS brain mapping of the pharyngeal cortical representation in healthy subjects

Abstract

a b s t r a c tBackground: Brain mapping is fundamental to understanding brain organization and function. However, a major drawback to the traditional Brodmann parcellation technique is the reliance on the use of postmortem specimens. It has therefore historically been difficult to make any comparison regarding functional data from different regions or hemispheres within the same individual. Moreover, this method has been significant limited by subjective boundaries and classification criteria and therefore suffer from reproducibility issues. The development of transcranial magnetic stimulation (TMS) offers an alternative approach to brain mapping, specifically the motor cortical regions by eliciting quantifiable functional reactions. Objective: To precisely describe the motor cortical topographic representation of pharyngeal constrictor musculature using TMS and to further map the brain for use as a tool to study brain plasticity. Methods: 51 healthy subjects (20 male/31 female, 19e26 years old) were tested using single-pulse TMS combined with intraluminal catheter-guided high-resolution manometry and a standardized grid cap. We investigated various parameters of the motor-evoked potential (MEP) that include the motor map area, amplitude, latency, center of gravity (CoG) and asymmetry index. Results: Cortically evoked response latencies were similar for the left and right hemispheres at 6.79 ± 0.22 and 7.24 ± 0.27 ms, respectively. The average scalp positions (relative to the vertex) of the pharyngeal motor cortical representation were 10.40 ± 0.19 (SE) cm medio-lateral and 3.20 ± 0.20 (SE) cm antero-posterior in the left hemisphere and 9.65 ± 0.24 (SE) cm medio-lateral and 3.18 ± 0.23 (SE) cm antero-posterior in the right hemisphere. The mean motor map area of the pharynx in the left and right hemispheres were 9.22 ± 0.85(SE) cm 2 and 10.12 ± 1.24(SE) cm 2 , respectively. The amplitudes of the MEPs were 35.94 ± 1.81(SE)uV in the left hemisphere and 34.49 ± 1.95(SE)uV in the right hemisphere. By comparison, subtle but consistent differences in the degree of the bilateral hemispheric representation were also apparent both between and within individuals. Conclusion: The swallowing musculature has a bilateral motor cortical representation across individuals, but is largely asymmetric within single subjects. These results suggest that TMS mapping using a guided Abbreviations: RMT, rest motor threshold; EMG, electromyography; MEPs, motor evoked potentials; MSO, maximum stimulator output; PMEP, pharyngeal motor evoked potential; CoG, center of gravity; UES, upper esophageal sphincter; HRM, solid-state high-resolution manometry; IC, intra-luminal catheter; SE, standard error of mean. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). (2020) 891e899 intra-pharyngeal EMG catheter combined with a standardized gridded cap might be a useful tool to localize brain function/dysfunction by linking brain activation to the corresponding physical reaction. Brain Stimu...

Localizing central swallowing functions by combining non-invasive brain stimulation with neuroimaging

“…Currently, the intraluminal pharyngeal electromyographic measurements are popularly used to detect the central swallowing excitability due to the potential reliability [7]. A recent study reported that eliciting pharyngeal MEPs is more difficult than those of other muscles [8]. Our pilot study, however, suggested that sEMG recordings of lip OO muscle activities through fMRI-guided nTMS could aid in the detection of the SMC muscles' MEPs for localization of the SMC target in M1.…”

Increased cortical-medulla functional connectivity is correlated with swallowing in dysphagia patients with subacute infratentorial stroke

“…Bilateral TMS stimulation of the motor cortex has been found to induce UES MEP ( Ertekin et al, 2001 ), and the demonstration of volitional control of UES relaxation with high-resolution manometry biofeedback ( Nativ‐Zeltzer et al, 2019 ) indicated cortical involvement in the regulation of the UES relaxation. Neuroanatomically, the corticobulbar tract originating from the lateral aspect of the primary motor cortex ( Hamdy, 2006 ) is located within the precentral gyrus, and the cricopharyngeus muscles receive fibers from both sides ( Li et al, 2020 , Aziz et al, 1996 ). Our findings on the correlation of UOD with the FC between the bilateral precentral gyrus and the medulla may be related to the role of the precentral gyrus in hyoid movement or to direct regulation of the relaxation aspect of the UES opening.…”

Swallowing function after acute ischemic stroke: Development and validation of a novel clinical prognostic model

“…The swallowing process remains controversial in terms of the degree of lateralization. Several studies have shown that swallowing exhibits asymmetries in the cerebral hemispheres ( 20 , 21 ). Studies have shown differences in swallowing physiology between right- and left-sided unilateral stroke patients, with pharyngeal damage being more severe in patients with right-hemisphere strokes ( 22 ).…”