Highlights
- •There exists electrophysiological and neuroradiological evidence that transcranial direct current stimulation (tDCS) modulates excitability of the swallowing-related cortical network. However, until now no studies have been performed evaluating the impact of non-invasive brain stimulation techniques on normal sucking and swallowing behavior.
- •Here, we provide initial evidence that tDCS may non-invasively modulate sucking behavior in healthy humans. tDCS, applied to the right swallowing motor cortex, significantly enhances sucking of a liquid bolus in normal subjects. tDCS acts mainly by prolonging the contraction time of the suprahyoid/submental muscles during suction.
- •Oropharyngeal dysphagia is a high-prevalence condition with enormous personal, social, and economic costs. The available treatment options are very limited. On the basis of our results in healthy subjects, we think that tDCS could become a very useful therapeutic tool for improving dysphagia in different pathological conditions, not least because it is easy to use, cost-effective, and offers the possibility of home treatment.
Abstract
Background
Transcranial direct current stimulation (tDCS) is a non-invasive technique used for
modulating cortical excitability in vivo in humans. Here we evaluated the effect of
tDCS on behavioral and electrophysiological aspects of physiological sucking and swallowing.
Methods
Twelve healthy subjects underwent three tDCS sessions (anodal, cathodal and sham stimulation)
on separate days in a double-blind randomized order. The active electrode was placed
over the right swallowing motor cortex. Repeated sucking and swallowing acts were
performed at baseline and at 15 and 60 min after each tDCS session and the mean liquid
bolus volume ingested at each time point was measured. We also calculated average
values of the following electrophysiological parameters: 1) area and 2) duration of
the rectified EMG signal from the suprahyoid/submental muscles related to the sucking
and swallowing phases; 3) EMG peak amplitude for the sucking and swallowing phases;
4) area and peak amplitude of the laryngeal-pharyngeal mechanogram; 5) oropharyngeal
delay.
Results
The volume of the ingested bolus significantly increased (by an average of about 30%
compared with the baseline value) both at 15 and at 60 min after the end of anodal
tDCS. The electrophysiological evaluation after anodal tDCS showed a significant increase
in area and duration of the sucking phase-related EMG signal.
Conclusions
Anodal tDCS leads to stronger sucking of a liquid bolus in healthy subjects, likely
by increasing recruitment of cortical areas of the swallowing network. This finding
might open up interesting perspectives for the treatment of patients suffering from
dysphagia due to various pathological conditions.
Keywords
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References
- Non-invasive brain stimulation in neurological diseases.Neuropharmacology. 2013; 64: 579-587
- Brain polarization in humans: a reappraisal of an old tool for prolonged non-invasive modulation of brain excitability.Clin Neurophysiol. 2003; 114: 589-595
- A sham-controlled, phase II trial of transcranial direct current stimulation for the treatment of central pain in traumatic spinal cord injury.Pain. 2006; 122: 197-209
- Modulation of motor performance and motor learning by transcranial direct current stimulation.Curr Opin Neurol. 2011; 24: 590-596
- Differences in the experience of active and sham transcranial direct current stimulation.Brain Stimul. 2012; 5: 155-162
- Sustained excitability elevations induced by transcranial DC motor cortex stimulation in humans.Neurology. 2001; 57: 1899-1901
- Outlasting excitability shifts induced by direct current stimulation of the human brain.Suppl Clin Neurophysiol. 2004; 57: 708-714
- Characterizing the application of transcranial direct current stimulation in human pharyngeal motor cortex.Am J Physiol Gastrointest Liver Physiol. 2009; 297: G1035-G1040
- Magnetoencephalographic evidence for the modulation of cortical swallowing processing by transcranial direct current stimulation.Neuroimage. 2013; 83: 346-354
- Noninvasive brain stimulation may improve stroke-related dysphagia: a pilot study.Stroke. 2011; 42: 1035-1040
- Transcranial direct current stimulation improves swallowing function in stroke patients.Neurorehabil Neural Repair. 2013; 27: 363-369
- Brain stem control of swallowing: neuronal network and cellular mechanisms.Physiol Rev. 2001; 81: 929-969
- Functional properties of neurons in the primate tongue primary motor cortex during swallowing.J Neurophysiol. 1997; 78: 1516-1530
- The cortical topography of human swallowing musculature in health and disease.Nat Med. 1996; 2: 1217-1224
- Task-dependent differences in corticobulbar excitability of the submental motor projections: Implications for neural control of swallowing.Brain Res Bull. 2011; 84: 88-93
- Cortical activation during human volitional swallowing: an event-related fMRI study.Am J Physiol. 1999; 277: G219-G225
- An electrophysiological investigation of deglutition in man.Muscle Nerve. 1995; 18: 1177-1186
- Evaluation of normal deglutition with the help of rectified surface electromyography records.Dysphagia. 2004; 19: 125-132
- Applied anatomy and physiology of the normal swallow.in: Cichero J. Murdoch B. Dysphagia. Foundation, theory and practice. John Wiley & Sons Ltd, Chichester2006: 3-146
- Control of tongue and facial motility: neural mechanisms that may contribute to movements such as swallowing and sucking.Symp Oral Sens Percept. 1973; 4: 222-231
- Timing of videofluoroscopic, manometric events, and bolus transit during the oral and pharyngeal phases of swallowing.Dysphagia. 1989; 4: 8-15
- Coordination of deglutitive glottic closure with oropharyngeal swallowing.Gastroenterology. 1990; 98: 1478-1484
- Evaluating the structural properties of suprahyoid muscles and their potential for moving the hyoid.Dysphagia. 2011; 26: 345-351
- The role of the cerebral cortex in swallowing.Dysphagia. 1993; 8: 195-202
- Cerebral cortical representation of automatic and volitional swallowing in humans.J Neurophysiol. 2001; 85: 938-950
- Compartmentalization of muscles and their motor nuclei: the partitioning hypothesis.Phys Ther. 1993; 73: 857-867
- Diverse firing properties of single motor units in the inner and outer portions of the guinea pig anterior digastric muscle.Arch Oral Biol. 1993; 38: 169-178
- Difference in the burst patterns of digastric and mylohyoid activities during feeding in the freely behaving rabbit.Dysphagia. 1999; 14: 78-84
- Heterogeneity within geniohyoid motor unit subpopulations in firing patterns during breathing.Respir Physiol. 2000; 124: 23-33
- Evidence for functional partitioning of the rabbit digastric muscle.Cells Tissues Organs. 2002; 170: 170-182
- Lateralization of cortical function in swallowing: a functional MR imaging study.AJNR Am J Neuroradiol. 1999; 20: 1520-1526
- Motor cortex activation is related to force of squeezing.Hum Brain Mapp. 2002; 16: 197-205
- Chewing and food consistency: effects on bolus transport and swallow initiation.Dysphagia. 2007; 22: 100-107
- Improved isometric force endurance after transcranial direct current stimulation over the human motor cortical areas.Eur J Neurosci. 2007; 26: 242-249
- Preliminary evidence that anodal transcranial direct current stimulation enhances time to task failure of a sustained submaximal contraction.PLoS One. 2013; 8: e81418
- Swallowing lateralization: the effects of modified dual-task interference.Dysphagia. 2006; 21: 21-27
- Lesion site in unilateral stroke patients with dysphagia.J Stroke Cerebrovasc Dis. 1996; 6: 30-34
- Effect of swallowed bolus variables on oral and pharyngeal phases of swallowing.Am J Physiol. 1990; 258: G675-G681
- Correspondence between food consistency and suprahyoid muscle activity, tongue pressure, and bolus transit times during the oropharyngeal phase of swallowing.J Appl Physiol. 2008; 105: 791-799
- Surface electromyographic activity of the submental muscles during swallow and expiratory pressure threshold training tasks.Dysphagia. 2007; 22: 108-116
- Motor enrichment and the induction of plasticity before or after brain injury.Neurochem Res. 2003; 28: 1757-1769
- Approaches to management of disordered swallowing.Baillieres Clin Gastroenterol. 1991; 5: 269-280
- Treatment of oral and pharyngeal dysphagia.Phys Med Rehabil Clin N Am. 2008; 19: 803-816
- Senescent swallowing: impact, strategies, and interventions.Nutr Clin Pract. 2009; 24: 395-413
Article info
Publication history
Published online: September 17, 2014
Accepted:
September 10,
2014
Received in revised form:
September 9,
2014
Received:
May 2,
2014
Footnotes
Conflict of interest: None of the authors of the above manuscript declare any conflict of interest.
This study was supported by a grant from the Italian Ministry of Health related to the Project “Presbyphagia: analysis of diagnostic criteria and identification of potential innovative treatments” (RF-2010-231945).
Identification
Copyright
© 2014 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
