Characterizing functional connectivity patterns during saliva swallows in different head positions

Electrophysiological Measures of Swallowing Functions: A Systematic Review

The purpose of this systematic review was to examine the application of event-related potentials (ERPs) to investigate neural processes of swallowing functions in adults with and without dysphagia. Computerized literature searches were performed from three search engines. Studies were screened using Covidence (Cochrane tool) and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement standards (PRISMA-2009). A total of 759 studies were initially retrieved, of which 12 studies met inclusion criteria. Electrophysiological measures assessing swallowing functions were identified in two major ERP categories: (1) sensory potentials and (2) pre-motor potentials. Approximately 80% of eligible studies demonstrated strong methodological quality, although most employed a case series or case-control study design. Pharyngeal sensory-evoked potentials (PSEPs) were used to assess pharyngeal afferent cortical processing. The temporal sequence of the PSEP waveforms varied based on the sensory stimuli. PSEPs were delayed with localized scalp maps in patients with dysphagia as compared to healthy controls. The pre-motor ERPs assessed the cortical substrates involved in motor planning for swallowing, with the following major neural substrates identified: pre-motor cortex, supplementary motor area, and primary sensorimotor cortex. The pre-motor ERPs differed in amplitude for the swallow task (saliva versus liquid swallow), and the neural networks differed for cued versus non-cued task of swallowing suggesting differences in cognitive processes. This systematic review describes the application of electrophysiological measures to assess swallowing function and the promising application for furthering understanding of the neural substrates of swallowing. Standardization of protocols for use of electrophysiological measures to examine swallowing would allow for aggregation of study data to inform clinical practice for dysphagia rehabilitation.

Can Swallowing Cerebral Neurophysiology Be Evaluated during Ecological Food Intake Conditions? A Systematic Literature Review

Swallowing is a complex function that relies on both brainstem and cerebral control. Cerebral neurofunctional evaluations are mostly based on functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), performed with the individual laying down; which is a non-ecological/non-natural position for swallowing. According to the PRISMA guidelines, a review of the non-invasive non-radiating neurofunctional tools, other than fMRI and PET, was conducted to explore the cerebral activity in swallowing during natural food intake, in accordance with the PRISMA guidelines. Using Embase and PubMed, we included human studies focusing on neurofunctional imaging during an ecologic swallowing task. From 5948 unique records, we retained 43 original articles, reporting on three different techniques: electroencephalography (EEG), magnetoencephalography (MEG) and functional near infra-red spectroscopy (fNIRS). During swallowing, all three techniques showed activity of the pericentral cortex. Variations were associated with the modality of the swallowing process (volitional or non-volitional) and the substance used (mostly water and saliva). All techniques have been used in both healthy and pathological conditions to explore the precise time course, localization or network structure of the swallowing cerebral activity, sometimes even more precisely than fMRI. EEG and MEG are the most advanced and mastered techniques but fNIRS is the most ready-to-use and the most therapeutically promising. Ongoing development of these techniques will support and improve our future understanding of the cerebral control of swallowing.

Impact of the Chin-Down Posture on Temporal Measures of Patients With Dysphagia: A Pilot Study

Purpose The chin-down position is a commonly prescribed posture by health care professionals to alleviate the symptoms of dysphagia. Yet, how the technique influences swallowing physiology lacks clarity. Our goal was to examine the impact of the postural technique on patients with various medical conditions and swallowing impairments. Method Temporal and functional measures were examined with videofluoroscopy in the chin-down and neutral head position on 15 patients. Also, timing differences between head positions were examined to determine the presence of improvement during the chin-down posture. Results The primary finding was chin-down posture swallows prolonged the elapsed time between when the prematurely spilled bolus entered the pharynx relative to swallow onset compared to the neutral head position (p = .006). Also, no improvement in airway protection was found when performing the postural technique. Conclusions The chin-down posture may benefit patients with specific swallowing impairments. However, the general use of the technique for all patients who experience swallowing difficulty might be negligent and could potentially have adverse or no effect on patient outcomes. Future studies examining patients with the same pathophysiology are needed to understand the benefit of the chin-down posture based on swallowing impairment.

A fast algorithm for vertex-frequency representations of signals on graphs

The windowed Fourier transform (short time Fourier transform) and the S-transform are widely used signal processing tools for extracting frequency information from non-stationary signals. Previously, the windowed Fourier transform had been adopted for signals on graphs and has been shown to be very useful for extracting vertex-frequency information from graphs. However, high computational complexity makes these algorithms impractical. We sought to develop a fast windowed graph Fourier transform and a fast graph S-transform requiring significantly shorter computation time. The proposed schemes have been tested with synthetic test graph signals and real graph signals derived from electroencephalography recordings made during swallowing. The results showed that the proposed schemes provide significantly lower computation time in comparison with the standard windowed graph Fourier transform and the fast graph S-transform. Also, the results showed that noise has no effect on the results of the algorithm for the fast windowed graph Fourier transform or on the graph S-transform. Finally, we showed that graphs can be reconstructed from the vertex-frequency representations obtained with the proposed algorithms.

Functional connectivity patterns of normal human swallowing: difference among various viscosity swallows in normal and chin-tuck head positions

Consuming thicker fluids and swallowing in the chin-tuck position has been shown to be advantageous for some patients with neurogenic dysphagia who aspirate due to various causes. The anatomical changes caused by these therapeutic techniques are well known, but it is unclear whether these changes alter the cerebral processing of swallow-related sensorimotor activity. We sought to investigate the effect of increased fluid viscosity and chin-down posture during swallowing on brain networks. 55 healthy adults performed water, nectar-thick, and honey thick liquid swallows in the neutral and chin-tuck positions while EEG signals were recorded. After pre-processing of the EEG timeseries, the time-frequency based synchrony measure was used for forming the brain networks to investigate whether there were differences among the brain networks between the swallowing of different fluid viscosities and swallowing in different head positions. We also investigated whether swallowing under various conditions exhibit small-world properties. Results showed that fluid viscosity affects the brain network in the Delta, Theta, Alpha, Beta, and Gamma frequency bands and that swallowing in the chin-tuck head position affects brain networks in the Alpha, Beta, and Gamma frequency bands. In addition, we showed that swallowing in all tested conditions exhibited small-world properties. Therefore, fluid viscosity and head positions should be considered in future swallowing EEG investigations.