Ruth E. Martin

The role of the cerebral cortex in swallowing

This paper reviews clinical, neuroanatomical, and neurophysiological studies that have implicated the cerebral cortex in the initiation and/or regulation of swallowing as well as related functions such as mastication. Cortical dysfunction has been reported to result in a variety of swallowing impairments. Furthermore, swallowing can be evoked and/or modulated by stimulation applied to restricted regions of the cortex. Neuroanatomical investigations and single neuron recording studies also provide some insights into the cortical structures, pathways, and mechanisms that may mediate deglutition.

A REVIEW OF THE RELATIONSHIP BETWEEN DYSPHAGIA AND MALNUTRITION FOLLOWING STROKE

OBJECTIVE To clarify the relationship between malnutrition and dysphagia following stroke. DESIGN Systematic review. METHODS All published trials that had examined both the swallowing ability and nutritional status of subjects following stroke were identified. Pooled analyses were performed to establish whether the odds of being malnourished were increased given the presence of dysphagia. RESULTS Eight studies were identified. The presence of malnutrition and dysphagia ranged from 8.2% to 49.0% and 24.3% to 52.6%, respectively. Five of the included trials were conducted within the first 7 days following stroke, while 3 were conducted during the rehabilitation phase. The overall odds of being malnourished were higher among subjects who were dysphagic compared with subjects with intact swallowing (odds ratio: 2.425; 95% confidence interval: 1.264-4.649, p < 0.008). In subgroup analysis, the odds of malnutrition were significantly increased during the rehabilitation stage (odds ratio: 2.445; 95% confidence interval: 1.009-5.925, p < 0.048), but not during the first 7 days of hospital admission (odds ratio: 2.401; 95% confidence interval: 0.918-6.277, p < 0.074). CONCLUSION In a systematic review including the results from 8 studies, the odds of being malnourished were increased given the presence of dysphagia following stroke.

Dysphagia following Anterior Cervical Spine Surgery

Abstract. Although previous reports have identified dysphagia as a potential complication of anterior cervical spine surgery (ACSS), current understanding of the nature and etiologies of ACSS-related dysphagia remains limited. The present study was undertaken to describe the patterns of dysphagia that may occur following ACSS. Thirteen patients who exhibited new-onset dysphagia following ACSS were studied retrospectively by means of chart review and videofluoroscopic swallow study analysis. Results indicated that a variety of swallowing impairments occurred following ACSS. In 2 patients, prevertebral soft tissue swelling near the surgical site, deficient posterior pharyngeal wall movement, and impaired upper esophageal sphincter opening were the most salient videofluoroscopic findings. In another 5 patients, the pharyngeal phase of swallowing was absent or very weak, with resulting aspiration in 3 cases. In contrast, an additional 4 patients exhibited deficits primarily of the oral preparatory and oral stages of swallowing including deficient bolus formation and reduced tongue propulsive action. Finally, 2 patients exhibited impaired oral preparatory and oral phases, a weak pharyngeal swallow, as well as prevertebral swelling. Thus, a variety of swallowing deficits, due possibly to neurological and/or soft tissue injuries, may occur following ACSS.

Cerebral cortical processing of swallowing in older adults

While brain-imaging studies in young adults have implicated multiple cortical regions in swallowing, investigations in older subjects are lacking. This study examined the neural representations of voluntary saliva swallowing and water swallowing in older adults. Nine healthy females were examined with event-related functional magnetic resonance imaging (fMRI) while laryngeal swallow-related movements were recorded. Swallowing in the older adults, like young adults, activated multiple cortical regions, most prominently the lateral pericentral, perisylvian, and anterior cingulate cortex. Activation of the postcentral gyrus was lateralized to the left hemisphere for saliva and water swallowing, consistent with our findings in young female subjects. Comparison of saliva and water swallowing revealed a fourfold increase in the brain volume activated by the water swallow compared to the saliva swallow, particularly within the right premotor and prefrontal cortex. This task-specific activation pattern may represent a compensatory response to the demands of the water swallow in the face of age-related diminution of oral sensorimotor function.

Face sensorimotor cortex and its neuroplasticity related to orofacial sensorimotor functions

This review describes evidence in subprimates and primates that the face primary somatosensory cortex (face SI) and primary motor cortex (face MI) are involved in sensorimotor integration and control of orofacial motor functions that include semiautomatic movements (e.g., chewing, swallowing) and voluntary movements (e.g., jaw-opening). The review also notes that the neuroplastic capabilities of the face SI and face MI have recently been documented, and may reflect or allow for functional adaptation (or maladaptation) of the orofacial sensorimotor system to an altered oral state or oral motor behaviour. They may contribute to the processes whereby patients undergoing oral rehabilitation can (or cannot) restore the lost orofacial sensorimotor functions. Such understanding is important since pain, injuries to the oral tissues, and alterations to the dental occlusion induced by tooth loss or attrition are common occurrences in humans that may sometimes be accompanied by impaired oral sensorimotor functions. Furthermore, impaired oral sensorimotor functions are common in many neurological disorders, sometimes making the most vital functions of eating, swallowing and speaking difficult and thereby reducing the patients quality of life. It has also been well documented that such negative consequences can be improved following oral rehabilitation as patients adapt, for example, to a new dental prosthesis aimed at restoring function. Therefore, understanding the mechanisms and cortical neuroplastic processes underlying orofacial sensorimotor functions and adaptation is also important for the development of new therapeutic strategies to facilitate recovery of patients suffering from orofacial pain and sensorimotor disorders and improve their quality of life.

Properties and plasticity of the primate somatosensory and motor cortex related to orofacial sensorimotor function.

1. The lateral pericentral region of the cerebral cortex has been well documented in primates to be important in sensorimotor integration and control and in the learning of new motor skills.

Discrete functional contributions of cerebral cortical foci in voluntary swallowing: a functional magnetic resonance imaging (fMRI) Go, No-Go study

Brain-imaging studies have shown that visually-cued, voluntary swallowing activates a distributed network of cortical regions including the precentral and postcentral gyri, anterior cingulate cortex (ACC), insula, frontoparietal operculum, cuneus and precuneus. To elucidate the functional contributions of these discrete activation foci for swallowing, a “Go, No-Go” functional magnetic resonance imaging (fMRI) paradigm was designed. Brain activation associated with visually-cued swallowing was compared with brain activation evoked by a comparable visual cue instructing the subject not to swallow. Region-of-interest analyses performed on data from eight healthy subjects showed a significantly greater number of activated voxels within the precentral gyrus, postcentral gyrus, and ACC during the “Go” condition compared to the “No-Go” condition. This finding suggests that the precentral gyrus, postcentral gyrus, and ACC contribute primarily to the act of swallowing. In contrast, the numbers of activated voxels within the cuneus and precuneus were not significantly different for the “Go” and “No-Go” conditions, suggesting that these regions mediate processing of the cue to swallow. Together these findings support the view that the discrete cortical foci previously implicated in swallowing mediate functionally distinct components of the swallowing act.

Relationships between speech intelligibility and the slope of second-formant transitions in dysarthric subjects

The relationship between speech intelligibility on a single-word identification test and the average second-formant (F2) slope of selected test words was examined for a group of 25 men and ten women with amyotrophic lateral sclerosis (ALS). A Spearman rank-order correlation coefficient greater than 0.80 was obtained for both the male and female subjects. This moderately high correlation indicates that the F2 slope index is a useful acoustic measure of speech proficiency in ALS. F2 slope indices are reported for normal control populations of geriatric men and women. In addition, progressive deterioration of the F2 slope index is illustrated in a case study of one woman with ALS.

Formant trajectory characteristics of males with amyotrophic lateral sclerosis

The purpose of this study was to describe the formant trajectories produced by males with amyotrophic lateral sclerosis (ALS), a degenerative neuromuscular disease that is typically associated with dysarthria. Formant trajectories of 25 males with ALS and 15 neurologically normal geriatric males were compared for 12 words selected from the speech intelligibility task developed by Kent et al. [J. Speech. Hear. Disord. 54, 482-499 (1989)]. The results indicated that speakers with ALS (1) produced formant transitions having shallower slopes than transitions of normal speakers, (2) tended to produce exaggerations of formant trajectories at the onset of vocalic nuclei, and (3) had greater interspeaker variability of formant transition characteristics than normal speakers. Within the group of ALS speakers, those subjects who were less than 70% intelligible produced distinctly more aberrant trajectory characteristics than subjects who were more than 70% intelligible. ALS subjects who were less than 70% intelligible produced many trajectories that were essentially flat, or that had very shallow slopes. These results are discussed in terms of the speech production deficit in the dysarthria associated with ALS, and with respect to the potential influence of aberrant trajectories on speech intelligibility.

Functional Brain Imaging of Swallowing: An Activation Likelihood Estimation Meta-Analysis

A quantitative, voxel‐wise meta‐analysis was performed to investigate the cortical control of water and saliva swallowing. Studies that were included in the meta‐analysis (1) examined water swallowing, saliva swallowing, or both, and (2) reported brain activation as coordinates in standard space. Using these criteria, a systematic literature search identified seven studies that examined water swallowing and five studies of saliva swallowing. An activation likelihood estimation (ALE) meta‐analysis of these studies was performed with GingerALE. For water swallowing, clusters with high activation likelihood were found in the bilateral sensorimotor cortex, right inferior parietal lobule, and right anterior insula. For saliva swallowing, clusters with high activation likelihood were found in the left sensorimotor cortex, right motor cortex, and bilateral cingulate gyrus. A between‐condition meta‐analysis revealed clusters with higher activation likelihood for water than for saliva swallowing in the right inferior parietal lobule, right postcentral gyrus, and right anterior insula. Clusters with higher activation likelihood for saliva than for water swallowing were found in the bilateral supplementary motor area, bilateral anterior cingulate gyrus, and bilateral precentral gyrus. This meta‐analysis emphasizes the distributed and partly overlapping cortical networks involved in the control of water and saliva swallowing. Water swallowing is associated with right inferior parietal activation, likely reflecting the sensory processing of intraoral water stimulation. Saliva swallowing more strongly involves premotor areas, which are crucial for the initiation and control of movements. Hum Brain Mapp, 2009.