A Study of Brain Networks Associated with Swallowing Using Graph-Theoretical Approaches

Functional connectivity between brain regions during swallowing tasks is still not well understood. Understanding these complex interactions is of great interest from both a scientific and a clinical perspective. In this study, functional magnetic resonance imaging (fMRI) was utilized to study brain functional networks during voluntary saliva swallowing in twenty-two adult healthy subjects (all females, 23.1±1.52 years of age). To construct these functional connections, we computed mean partial correlation matrices over ninety brain regions for each participant. Two regions were determined to be functionally connected if their correlation was above a certain threshold. These correlation matrices were then analyzed using graph-theoretical approaches. In particular, we considered several network measures for the whole brain and for swallowing-related brain regions. The results have shown that significant pairwise functional connections were, mostly, either local and intra-hemispheric or symmetrically inter-hemispheric. Furthermore, we showed that all human brain functional network, although varying in some degree, had typical small-world properties as compared to regular networks and random networks. These properties allow information transfer within the network at a relatively high efficiency. Swallowing-related brain regions also had higher values for some of the network measures in comparison to when these measures were calculated for the whole brain. The current results warrant further investigation of graph-theoretical approaches as a potential tool for understanding the neural basis of dysphagia. © 2013 Luan et al

Differential psychophysiological interactions of insular subdivisions during varied oropharyngeal swallowing tasks

Abstract The insula is a highly integrated cortical region both anatomically and functionally. It has been shown to have cognitive, social–emotional, gustatory, and sensorimotor functions. Insular involvement in both normal and abnormal swallowing behavior is well established, yet its functional connectivity is unclear. Studies of context‐dependent connectivity, or the connectivity during different task conditions, have the potential to reveal information about synaptic function of the insula. The goal of this study was to examine the functional connectivity of specific insular regions (ventral anterior, dorsal anterior, and posterior) with distant cortical regions during four swallowing conditions (water, sour, e‐stim, and visual biofeedback) using generalized psychophysiological interactions (gPPI). In 19 healthy adults, we found that the visual biofeedback condition was associated with the most and strongest increases in functional connectivity. The posterior insula/rolandic operculum regions had the largest clusters of increases in functional connectivity, but the ventral anterior insula was functionally connected to a more diverse array of cortical regions. Also, laterality assessments showed left lateralized increases in swallowing functional connectivity. Our results are aligned with reports about the insula's interconnectivity and extensive involvement in multisensory and cognitive tasks

Meta-Analytic Connectivity Modelling of Healthy Swallowing

A quantitative, voxel-wise meta-analysis was performed to investigate the brain regions involved in healthy human swallowing. Studies included in the meta-analysis (1) examined water swallowing, saliva swallowing, or both, (2) included healthy, normal subjects, and (3) reported stereotaxic brain activation coordinates in standard space. Following these criteria, a systematic literature review identified 8 studies that met the criteria. An activation likelihood estimation (ALE) meta-analysis and meta-analytic connectivity modelling (MACM) analysis were performed with BrainMap software. Ten clusters with high activation likelihood were found in the bilateral precentral gyri, right insula, left declive, right medial frontal gyrus, right dorsal nucleus of the thalamus, and the bilateral dentate nuclei of the cerebellum. Meta-analytic connectivity modelling revealed functional two-way and one-way connections between the regions, forming an interconnected network. Together, these finding indicate an extensive swallowing network made up of the key activated regions and the associated areas within those regions

The effect of taste on swallowing function

This study investigated the effects of taste on swallowing frequency and cortical activation in the swallowing network. The effects of salivary flow and taster status were also examined, along with genetic taster status. The effects of a 3ml bolus compared sour, sour with slow infusion, sweet, water, and water with infusion. Swallowing frequency was significantly higher 0-15 seconds after bolus delivery than 16-30 seconds. Swallowing frequency was higher in the sour conditions, whereas sweet and water did not differ. Functional near-infrared spectroscopy recordings measured changes in blood oxygenation (HbO) in the right and left hemispheres in the premotor, S1 and supplementary motor area in response to swallowing a bolus indicated a significant interaction of side and channel. Event-related analyses of HbO following bolus administration of taste solutions were significantly higher in the sensory than the premotor area in the right hemisphere. A block average analysis of the response to taste between 17 and 22 seconds after bolus administration revealed significant differences between hemispheres and regions. Genetic taster status was not significant in any of the analyses. The highest activation in response to sour taste was in the premotor regions of both hemispheres. The results indicated that sour taste effectively increased swallowing frequency and cortical activation while increasing salivary flow in comparison to water and sweet taste. In conclusion, sour taste may have peripheral effects on salivary flow while up-regulating the activation of the swallowing network at the cortical level

Role Of Cerebellum In Deglutition And Deglutition Disorders

The objective of this review is to gather available evidence regarding the role of the cerebellum in swallowing- related functions. We reviewed literature on cerebellar func- tions related to healthy swallowing, patterns of dysphagia in individuals with cerebellar lesions, and the role of the cere- bellum in therapeutic intervention of neurogenic dysphagia since 1980. A collective understanding of these studies sug- gests that both hemispheres of the cerebellum, predominantly the left, participate in healthy swallowing. Also, it appears that the cerebellum contributes to specific physiological functions within the entire act of swallowing, but this is not clearly understood. The understanding of patterns of dysphagia in cerebellar lesions remains ambiguous with equivocal results across a small number of studies. The cerebellum appears to be involved in oral exercises for dysphagia in the relationship between oral movements in such exercises, and deglutition remains uncertain. There is increasing evidence to suggest successful use of transcranial magnetic stimulation of the cerebellum to improve neuromotor control of swallowing. Future studies should address activation of the cerebellum with swallowing of different consistencies and tastes in healthy adults to gain better insights. Studies should also investigate dynamics of neural activation during different stages of recovery from dysphagia following strokes to corti- cal centers to determine if the cerebellum plays a compensa- tory role during instances of increased neural demands

Basic taste processing recruits bilateral anteroventral and middle dorsal insulae: An activation likelihood estimation meta-analysis of fMRI studies

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Mapping the Spatial and Temporal Dynamics of Sensorimotor Integration During the Perception and Performance of Wallowing

Similar to other complex sequences of muscle activity, swallowing relies heavily upon ‘sensorimotor integration.’ It is well known that the premotor cortex and primary sensorimotor cortices provide critical sensorimotor contributions that help control the strength and timing of swallowing muscle effectors. However, the temporal dynamics of sensorimotor integration remains unclear, even when performed normally without neurological compromise. Recent advances in EEG analysis blind source separation techniques via independent component analysis offer a novel and exciting opportunity to measure cortical sensorimotor activity in realtime during swallowing, concurrently with muscle activity during swallow initiation. In the current study, mu components were identified, with characteristic alpha (~10 Hz) and beta (~20 Hz) frequency bands. Spectral power within these frequency bands are known to index somatosensory and motor activity, respectively. Twenty-five adult participants produced swallowing and tongue tapping (motor control) tasks. Additionally they were asked to watch a video depicting swallowing and a scrambled kaleidoscope (perceptual control) version of this same video. Independent component analysis of raw EEG signals identified bilateral clusters of mu components, maximally localized to the premotor cortex (BA6) in 19 participants during the production and the perception tasks. Event related spectral perturbation (ERSP) analysis was used to identify spectral power within alpha and beta peaks of the mu cluster across time. Alpha and beta event-related desynchronization (ERD), indicative of somatosensory and motor activity, was revealed for both tongue tapping and swallowing beginning at ~500 ms following a visual cue to “go.” However, the patterns of ERD are stronger (pFD