Effects of cerebellar transcranial direct current stimulation (tDCS) on motor skill learning in swallowing.

OBJECTIVE: This study evaluated the effects of cerebellar tDCS on motor learning for swallowing. METHODS: In a double-blind RCT, 39 healthy adults received either sham, anodal tDCS, or cathodal tDCS in two sessions on two consecutive days. Following 20 min cerebellar tDCS (2 mA) or sham, they underwent swallowing skill training that targeted control of timing and magnitude of submental muscle activation during swallowing. Linear mixed models were used to identify the effects of stimulation on timing and magnitude accuracy as measured by the change in task performance for each training session, and for skill retention on days 3 and 10 post-intervention. RESULTS: Only the sham group had a reduced temporal error from baseline to all following timepoints. When compared to error changes in the sham group, changes from baseline in temporal errors were higher at all timepoints post-intervention for the anodal group, and higher at both retention assessments for the cathodal group. Amplitude errors were smaller for all conditions at all timepoints post-intervention compared to baseline. CONCLUSIONS: Cerebellar tDCS was found to inhibit temporal aspects of motor skill learning in swallowing. For the tDCS parameters used in this study, there is no support for use of tDCS to facilitate swallowing rehabilitation. Trial Registry Number (https://www.anzctr.org.au/): ACTRN12615000451505.IMPLICATIONS FOR REHABILITATIONCerebellar tDCS, in combination with motor skill training, has been demonstrated to increase motor skill learning in healthy individuals and neurologically impaired patients.In this study, cerebellar tDCS applied prior to swallowing skill training adversely affected timing measures of submental muscle activation during swallowing.In contrast to published outcomes in the corticospinal literature, both anodal and cathodal tDCS resulted in a relative inhibitory effect on motor skill learning in swallowing when compared to the sham condition.Swallowing skill training without tDCS produced increased accuracy in outcomes.

The effect of swallowing treatments on corticobulbar excitability: a review of transcranial magnetic stimulation induced motor evoked potentials.

Transcranial magnetic stimulation (TMS) has been used extensively as a method of investigating the corticomotor physiology of many motor tasks, including healthy and disordered swallowing. Changes in excitability of cortical projections to various swallowing muscles have been documented in response to treatments with TMS induced motor evoked potentials (MEPs). These studies have provided valuable insight into CNS response to swallowing impairment, and more importantly, the adaptations associated with functional recovery. However, unique obstacles are presented when investigating corticobulbar neurophysiology associated with the complex task of swallowing. Stringent methodological control and supplementary outcome measures are required to ensure robust and clinically applicable findings. This article offers a tutorial for the researcher who may be considering the use of TMS for investigating changes in cortical excitability associated with various swallowing paradigms. Included is a review of the mechanisms of TMS and what can be measured with this technique, a summary of existing research using MEPs to investigate swallowing, a review of methodological factors that may influence outcomes, and proposed directions for new areas of research.

Cross-sectional area of the anterior belly of the digastric muscle: comparison of MRI and ultrasound measures.

Changes in morphometry of head and neck muscles have received little attention in research relative to limb muscles. While recent literature suggests that high-frequency ultrasound transducers can provide superior spatial resolution compared to that of magnetic resonance imaging (MRI), no studies have compared these imaging methods for investigating the submental muscle group. This preliminary study sought to compare ultrasound and MRI as a method of quantifying the cross-sectional area (CSA) of the submental muscle group. Measurements were taken from coronal ultrasound and MRI images in 11 healthy participants. Comparisons were limited to the anterior belly of the digastric muscle because of differences in imaging resolution. Ultrasound CSA measurements were smaller than MRI measurements (p = 0.01) by 10 % (95% CI = -18 to -2). Correlations were significant and relatively high (left: r = 0.909, p < 0.001; right: r = 0.776, p = 0.005). Ultrasound imaging has the advantages of natural participant positioning, superior clarity of muscle borders of the submental muscles, requires less acquisition time, and is a less expensive method of imaging compared to MRI. This preliminary study has shown that ultrasound is a viable imaging modality for quantitative measurements of the anterior belly of the digastric muscle and has advantages over MRI beyond cost and accessibility.

Electrical stimulation and swallowing: how much do we know?

Consequences of dysphagia substantially reduce quality of life, increase the risk of medical complications and mortality, and pose a substantial cost to healthcare systems. As a result, it is of no wonder that the clinical and scientific communities are showing interest in new avenues for dysphagia rehabilitation. Electrical stimulation (e-stim) for the treatment of swallowing impairments is among the most studied swallowing interventions in the published literature, yet many unanswered questions about its efficacy remain. In the meantime, many speech-language pathologists who treat dysphagia are attending educational and training sessions to obtain certifications to use this technique. Here, we review the values and limitations of the published literature on the topic of e-stim for swallowing to assist clinicians in decision making in their clinical practice. The discussion provides a review of swallowing anatomy and physiology, the fundamentals of e-stim, and information essential for the readers' independent critique of these studies--all of which are crucial for evaluating the possible effects of e-stim.

Intra- and inter-rater reliability for analysis of hyoid displacement measured with sonography.

PURPOSE: Anterior hyoid displacement is essential for efficient swallowing and is usually investigated with videofluoroscopy. Ultrasound offers a less expensive and noninvasive method of investigation. The present study investigated the viability of a novel method of quantifying hyoid displacement from sonograms using an anatomic reference point, through an evaluation of inter- and intra-rater reliability. METHODS: Three raters reviewed the sonographic video sweeps of five discrete swallows from each of five participants for inter-rater reliability. The primary investigator measured each swallow on two occasions for intra-rater reliability. Electronic calipers were used to measure distances from a "rest" frame prior to the swallow of interest and a "maximal displacement" frame, at which the hyoid bone was at maximal anterior displacement during each swallow. RESULTS: Single-measure intraclass correlation coefficient was high for inter-rater agreement at 0.86 for rest measures and 0.86 for maximal displacement. Intra-rater reliability was even higher at 0.95 for rest and 0.98 for maximal displacement. CONCLUSIONS: These preliminary results suggest that by using a novel analysis approach involving an anatomic reference point, raters can achieve high agreement on measurement of position of hyoid at maximal displacement relative to rest.

Pharyngeal pressures during swallowing within and across three sessions: within-subject variance and order effects.

No studies have investigated within-subject variation in measures of pharyngeal pressures during swallowing across sessions. This study aimed to document the variation in pharyngeal pressures both within and across three sessions. Twenty healthy participants were recruited for three sessions. For each session, peak or nadir pressures were recorded from the upper pharynx (sensor 1), mid-pharynx (sensor 2), and upper esophageal sphincter (sensor 3) during saliva and 10-ml water bolus swallows. Variance was larger across sessions than within sessions for sensors 1 and 2 but comparable for sensor 3. For all sensors there was a high correlation between the variance across sessions and within session (r = 0.92, p < 0.0001). There were no significant order effects of session or of trial at any sensor with estimated order effects less than 2% and the estimated maximum possible change no larger than 5% for trial and no larger than 12% for session. These data offer direction for longitudinal treatment studies in which pharyngeal pressures are an outcome measurement by (1) providing a basis for power calculations, (2) estimating the likely values of any confounding order effects, and (3) providing suggestions for more reliable data analysis.