CASE REPORT Open Access
Stuttered swallowing: Electric stimulation of the
right insula interferes with water swallowing.
A case report
Peter Sörös1,2*, Faisal Al-Otaibi2, Savio WH Wong3,4, J Kevin Shoemaker3, Seyed M Mirsattari2, Vladimir Hachinski2,
Ruth E Martin1,5
Abstract
Background: Various functional resonance imaging, magnetoencephalographic and lesion studies suggest the
involvement of the insular cortex in the control of swallowing. However, the exact location of insular activation
during swallowing and its functional significance remain unclear.
Case presentation: Invasive electroencephalographic monitoring was performed in a 24-year-old man with
medically intractable stereotyped nocturnal hypermotor seizures due to a ganglioglioma. During stimulation of the
right inferior posterior insular cortex with depth electrodes the patient spontaneously reported a perception of a
“stutter in swallowing”. Stimulation of the inferior posterior insular cortex at highest intensity (4 mA) was also
associated with irregular and delayed swallows. Swallowing was not impaired during stimulation of the superior
posterior insular cortex, regardless of stimulation intensity.
Conclusions: These results indicate that the right inferior posterior insular cortex is involved in the neural circuitry
underlying the control of swallowing.
Background
Swallowing is a complex sensorimotor function invol-
ving the coordinated activation of orofacial, pharyngeal,
laryngeal, respiratory, and esophageal muscles. Although
once attributed to brainstem circuits, electrophysiologic
studies in animals [1], and functional brain-mapping in
humans [2-4] have also implicated a distributed cortical-
subcortical network in swallowing neural control invol-
ving the bilateral primary sensorimotor cortex, premotor
and cingulate motor areas, frontoparietal operculum,
and the insula (for review, see [5-7]). The notion of a
cortical-subcortical network controlling swallowing is
further supported by lesion studies in humans [8-11].
Although various lines of evidence, supported by
functional resonance imaging [3,12], magnetoencephalo-
graphy [13] and lesion data [8], point at the involve-
ment of the insular cortex in the control of swallowing,
the exact involvement of the insula and its functional
significance remain unclear. While the right anterior
insula has been particularly implicated in swallowing
impairment [11,14], brain-imaging studies of swallowing
have reported both anterior and posterior insular activa-
tion. A recent quantitative meta-analysis of swallow-
related brain activity reported high activation likelihood
in the right anterior insular cortex for water swallowing,
and in the right posterior insula for voluntary saliva
swallowing [15].
Studying swallowing neural control is not only
important for basic neurophysiological research but
also from a clinical perspective because injury to the
central nervous system such as stroke frequently
results in significant swallowing impairment [16].
Indeed, brain injury can give rise to severe and pro-
tracted swallowing impairment, which necessitates tube
feeding. Current understanding of the neuropathophy-
siology of swallowing impairment, the neuroplastic
mechanisms underlying swallowing recovery, as well as
the principles of swallowing rehabilitation is limited
(for review, see [17]).
* Correspondence: peter.soros@gmail.com
1School of Communication Sciences and Disorders, University of Western
Ontario, London, Ontario, Canada
Full list of author information is available at the end of the article
Sörös et al. BMC Neurology 2011, 11:20
http://www.biomedcentral.com/1471-2377/11/20
© 2011 Sörös et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.

Case presentation
Electrical stimulation of the right posterior insular
cortex was performed in a 24-year-old right-handed
man who developed medically intractable epilepsy at the
age of 17 years and who was referred for invasive elec-
troencephalographic monitoring and pre-surgical map-
ping. He was suffering from stereotyped nocturnal
hypermotor seizures nearly every night. His neurological
examination was normal. MRI of the brain showed a
well-circumscribed tumor (18 × 12 × 11 mm) in the
right posterior insular cortex (Figure 1A).
Pre-surgical electric stimulation was performed using
depth electrodes that were implanted in the right pos-
terior insular cortex, above and below the tumor (1 mm
diameter size; Ad Tec Medical Instrument Corp.,
Racine, WI, USA) [18]. The depth electrodes were
inserted stereotactically using a Leksell stereotactic
frame and a Stealth station planning system (Medtronic-
Sofamor Danek, Minneapolis, MN, USA). The depth
electrode lines had 8 contacts (each 2 mm long) sepa-
rated by 2 mm. A transopercular approach was used to
implant the depth electrodes in the right insular cortex
above and below the lesion. The distal electrode con-
tacts of each depth line were located within the right
posterior insular cortex. Location of the electrode con-
tacts was confirmed by fusing a pre-implantation MRI
to a post-implantation CT scan with the aid of a volu-
metric mutual information algorithm using the Atamai
software (Atamai, Inc., London, ON, Canada; Figure 1B).
High frequency (50 Hz) bipolar electric impulses were
applied at four different intensity levels (1, 2, 3 and 4
mA) with a pulse duration of 0.3 ms over 2 s (Grass
Technologies, West Warwick, RI, USA). To assess the
potential impact of surgery on swallowing, the patient
swallowed a continuous water infusion (1 ml/s) delivered
manually to the mouth via a catheter-tipped syringe.
During water swallowing, electrodes S-pIC (superior pos-
terior insular cortex) and I-pIC (inferior posterior insular
cortex) were stimulated individually with increasing sti-
mulation intensities. Swallowing was recorded from the
output of a laryngeal movement sensor.
Stimulation with electrode I-pIC at 4 mA was associated
with a dysrhythmic pattern of swallowing as indicated by
irregular and delayed swallows (Figure 2A). Moreover, at
all intensity levels of stimulation with electrode I-pIC, the
patient spontaneously reported a perception of a “stutter
in swallowing”. In contrast, swallowing was not impaired
during stimulation with S-pIC, regardless of stimulation
intensity (Figure 2B). EEG recordings revealed that all epi-
leptic spikes and seizures originated from the right inferior
posterior insular cortex.
The tumor was surgically removed after invasive elec-
troencephalographic monitoring and diagnosed as a
ganglioglioma, a mostly benign neoplasm arising from
ganglion cells. Gangliogliomas are often located in the
medial and lateral temporal lobes, superior and middle
temporal gyri, parahippocampal gyrus and amygdala
[19], but can be found anywhere in the brain. Ganglio-
gliomas are a frequent cause of intractable epilepsy [20].
The patient has been seizure free after removal of the
ganglioglioma.
Conclusions
The insula is a phylogenetically old, as well as cytoarchi-
tectonically and functionally diverse area, integrating
information from numerous distinct regions of the
B
I-pIC
S-pIC
R L
A
Figure 1 Tumor location and electrode placement. A) Coronal T2-weighted anatomical MRI showing a lesion with increased signal intensity
in the right posterior insula marked by an arrowhead. This lesion was subsequently resected and was consistent with a ganglioglioma.
B) Superimposed coronal CT and MRI images showing 3 implanted depth electrode strips in the right hemisphere. The top two lines were
implanted in the insular cortex and the bottom line was inserted into the hippocampus and parahippocampus. Electrodes I-pIC (inferior
posterior insular) and S-pIC (superior posterior insular cortex) were stimulated to investigate insular involvement in the cerebral control of
swallowing.
Sörös et al. BMC Neurology 2011, 11:20
http://www.biomedcentral.com/1471-2377/11/20
Page 2 of 4

brain. Lesion studies [11,14] and functional brain imaging
[12] have suggested that the anterior insular cortex is
involved in the control of swallowing. The anterior insula
has been implicated in the processing of visceral sensa-
tion from the pharynx [21], esophagus and gastrointest-
inal tract [22], vibrotactile stimulation [23], gustation
[24], olfaction [25], and emotions such as disgust [26].
Other fMRI studies, however, reported swallow-related
activation of the posterior insula [3], which is involved in
autonomic regulation [18,27], including heart rate and
respiration. Consistent with this, a meta-analysis of swal-
low-related brain imaging implicated both the anterior
and posterior insula in swallowing [15].
Notwithstanding the possibility that slow tumor
growth may have engaged compensatory swallowing
mechanisms [28], the present finding that electrical sti-
mulation of the right inferior posterior insula disrupts
rhythmic water swallowing provides further evidence
that the posterior insular cortex is involved in the neural
circuitry underlying the control of swallowing.
Our results are consistent with previous cortical sti-
mulation studies of the posterior insular cortex which
resulted in visceral sensations and interference with
swallowing [29]. Recently, detailed mapping of the insu-
lar cortex in epilepsy patients has been performed using
electrical stimulation [30,31]. In 50 patients, electrical
stimulation of the anterior and posterior insular cortex
elicited 125 clinical responses, 22% of which involved a
viscerosensory effect. Half of these viscerosensory
responses consisted of sensations of unpleasant laryngo-
pharyngeal constriction [30]. In one patient, sponta-
neous seizures originated from the right anterior insular
cortex and quickly propagated to the right posterior
insular cortex [30]; these seizures began with strong lar-
yngeal discomfort and an unpleasant sensation of con-
striction, similar to the viscerosensory sensations elicited
by electrical stimulation [30]. Another insular mapping
study, again using electrical stimulation in epilepsy
patients, reported that insular stimulation evoked sensa-
tions of a pharyngeal constriction and a sensation of
swallowing associated with mastication [31].
The strong representation of viscerosensory afferents
in the insular cortex, as indicated by electrophysiological
recordings [30] and functional neuroimaging data [21],
as well as the importance of upper airway sensory input
for the control of swallowing [32], raises the possibility
that the disruption of water swallowing observed in our
patient may have been related to oropharyngeal-
laryngeal sensory alterations, such as discomfort or con-
striction, elicited by the electrical stimulation. Although
our patient did not report isolated upper airway sensations
during the stimulation protocol, it is conceivable that dis-
ruption of oropharyngeal-laryngeal sensory processing
may have interfered with normal water swallowing and
time (s)
vo
lta
ge
(m
V)
0 500 1000 1500 2000 2500 3000
-0.
5
0.0
0.5
SL-D1 (4 mA)
water infusion
B
time (s)
vo
lta
ge
(m
V)
0 500 1000 1500 2000 2500 3000
-0.
5
0.0
0.5
IL-D1 (4 mA)
water infusion
AA
B
5 1 15 2 25 3
5 1 15 2 25 3
I-pIC (4 m )
S-pIC (4 )
Figure 2 Recordings of swallowing-related laryngeal movements. Recording of laryngeal movements associated with water swallowing
during electrical stimulation of electrode I-pIC (inferior posterior insular cortex, A) and S-pIC (superior posterior insular cortex, B), both at 4 mA.
The grey area represents the electric stimulation (2 s), the black line the duration of continuous water infusion.
Sörös et al. BMC Neurology 2011, 11:20
http://www.biomedcentral.com/1471-2377/11/20
Page 3 of 4

created the impression of “stuttered swallowing”. Alterna-
tively, disruption of water swallowing in the present case
may have occurred due to an effect of insular stimulation
on swallowing motor execution. Further studies are
required to elucidate the mechanisms underlying the swal-
lowing phenomena documented in this clinical case.
Acknowledgements
Written consent for publication was obtained from the patient.
Author details
1School of Communication Sciences and Disorders, University of Western
Ontario, London, Ontario, Canada. 2Department of Clinical Neurological
Sciences, University of Western Ontario, London, Ontario, Canada. 3School of
Kinesiology, University of Western Ontario, London, Ontario, Canada. 4Brain
and Creativity Institute, University of Southern California, Los Angeles,
California, USA. 5Department of Physiology and Pharmacology, University of
Western Ontario, London, Ontario, Canada.
Authors’ contributions
PS analyzed the data and drafted the manuscript. FAO and SWHW
participated in data acquisition. JKS and SMM conceived the study,
participated in its design and in data acquisition. VH participated in analysis
and interpretation of the data. REM conceived and designed the study,
participated in data acquisition and analysis and drafted the manuscript. All
authors read and approved the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 29 September 2010 Accepted: 5 February 2011
Published: 5 February 2011
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Pre-publication history
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Cite this article as: Sörös et al.: Stuttered swallowing: Electric
stimulation of the right insula interferes with water swallowing. A case
report. BMC Neurology 2011 11:20.
Sörös et al. BMC Neurology 2011, 11:20
http://www.biomedcentral.com/1471-2377/11/20
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