585195
research-article2015

EEGXXX10.1177/1550059415585195Clinical EEG and NeuroscienceTezer et al

Original Article

Reflex Seizures Triggered by Exposure to
Characters With Numerical Value: A Case
With Right Temporal Cortical Dysplasia

Clinical EEG and Neuroscience
1­–4
© EEG and Clinical Neuroscience
Society (ECNS) 2015
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DOI: 10.1177/1550059415585195
eeg.sagepub.com

Şefik Evren Erdener1, F. Irsel Tezer1, Kader K. Oğuz2, Özden Kamışlı3,
Eser Lay Ergün4, Figen Söylemezoğlu5, and Serap Saygi1

Abstract
Reflex seizures can be triggered by a variety of stimuli. We present a case with drug-resistant complex partial seizures originating
in right temporal lobe triggered extensively by visual, auditory, and mental exposure to multidigit numbers. The patient was
investigated in video-EEG monitoring unit and seizures were triggered by numerical stimuli. Scalp EEG findings suggested a
right temporal focus but ictal semiological findings suspicious for an extratemporal area necessitated the invasive EEG study.
A right anterior temporal seizure focus was established with invasive monitoring and cortical stimulation studies. Magnetic
resonance imaging showed a cortical dysplasia in right anterior temporal lobe and ictal single-photon emission computed
tomography confirmed the epileptogenic focus, leading to a right temporal lobectomy and amygdalohippocampectomy and a
pathological diagnosis of focal cortical dysplasia type Ia. The patient is seizure-free at the end of the second postoperative year
despite repeated exposures to numbers. To our knowledge, this is the first report of seizures triggered by numbers. It is also of
particular importance as the reflex seizures are associated with a cortical lesion and it may suggest involvement of right anterior
temporal lobe in numerical processing.
Keywords
reflex seizures, temporal lobe, numbers, cortical dysplasia, video-EEG monitoring
Received January 12, 2015; revised March 8, 2015; accepted April 7, 2015.

Introduction
Reflex seizures can be triggered by a wide variety of stimuli.1-6
They can rarely be associated with cortical lesions,7 providing
clues to understand also neurobiology of specific cognitive
processes. Although calculation-induced seizures are well
known,2,6,8 there is no previous report on seizures triggered
with exposure to characters with numerical value. Here we
present a case with complex partial seizures associated with
cortical dysplasia and induced exclusively by numbers.

revealed sharp waves and spikes on the right frontotemporal areas.
Typical seizures were triggered by keeping the patient look at a
table with multiple-digit numbers or at a telephone keypad. The
recorded seizures were alike; onset was a few minutes after the
patient started looking at the numbers. Only one seizure was
triggered as the patient unexpectedly heard a telephone number
on TV; this time the seizure started approximately 2 seconds
following stimulus. Initial ictal sign was numbness in chest, left
arm, and shoulder. It was followed by a facial expression of
1

Case Study
A 36-year-old right-handed female patient was experiencing
seizures since she was 12 years old. The seizures occurred after
seeing numbers with multiple digits, such as telephone numbers or price tags, but they could also be induced by hearing,
thinking about, or writing down such numbers. Besides those
provoked seizures, she could also experience spontaneous ones
as well. Seizures were refractory to levetiracetam and carbamazepine. The neurologic examination was normal.
The patient was admitted to our video-electroencephalography
(video-EEG) monitoring unit for seizure recording. Interictal EEG

Department of Neurology, Faculty of Medicine, Hacettepe University,
Ankara, Turkey
2
Department of Radiology, Faculty of Medicine, Hacettepe University,
Ankara, Turkey
3
Department of Neurology, Faculty of Medicine, Inonu University, Malatya,
Turkey
4
Department of Nuclear Medicine, Faculty of Medicine, Hacettepe
University, Ankara, Turkey
5
Department of Pathology, Faculty of Medicine, Hacettepe University,
Ankara, Turkey
Corresponding Author:
F. Irsel Tezer, Department of Neurology, Hacettepe University Hospitals,
Ankara 06100, Turkey.
Email: irseltezer@yahoo.com.tr

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Figure 1. (A) Coronal T2-weighted magnetic resonance imaging (MRI) series showing a probably dysplastic cortex (arrow) in right
anterior temporal lobe. (B) Ictal brain perfusion single-photon emission computed tomography (SPECT) images demostrates significant right
temporal hyperperfusion (thick arrows) slightly extending to the right parietal and frontal regions (thin arrows).

pain or crying, tonic posture in left arm, oral and right-sided
automatisms (supplementary video, available at http://eeg.sagepub.com/content/by/supplemental-data). Each seizure typically
lasted for 45 seconds followed by postictal paresis in left arm
for 3 minutes. The ictal EEG findings revealed a short-lasting
initial rhythmic sharp theta activity in right temporal lobe followed by rhythmic delta waves. Magnetic resonance imaging
(MRI) demonstrated mild T2A hyperintensity and corticomedullary blurring in right anterior temporal lobe, suggesting a
cortical dysplasia (Figure 1A). There was no pathological sign
in parietal cortices. Ictal brain perfusion single-photon emission
computed tomography (SPECT) was obtained and it showed
significant right temporal hyperperfusion slightly extending
through the right parietal and frontal regions (Figure 1B).
Furthermore, her neuropsychological examination revealed
moderate right parietal and hippocampal dysfunctions.
Although all neuroimaging and scalp EEG findings supported the presence of a right temporal epileptogenic area, an
extratemporal focus was considered because of the initial ictal
semiology findings like paresthesias. We performed invasive
EEG recording including the right temporal and parietal area
(Figure 2A). Very frequent interictal spikes were recorded in
right mesial temporal electrodes and also in right inferior parietal areas. Interictal epileptiform activity increased with visual
numerical stimulation. Initial ictal EEG changes revealed right
temporal lobe onset (Figure 2B; supplementary video). Cortical
mapping study was performed with 50-Hz, 300-ms electrical
stimulation of subdural electrodes. When posterior mesial temporal electrodes were stimulated with 2.5 mA current, frequent
epileptiform discharges appeared in posterior and anterior temporal electrodes simultaneously with numbness symptom in
left shoulder. Ten seconds later, a typical complex partial seizure was recorded with similar ictal EEG changes as reported
above. Stimulation of extratemporal areas did not end up with
clinical seizure or epileptiform activity.
After confirming the seizure focus as a right mesial temporal
lobe and considering the right hippocampal dysfunction on her
neuropsychological tests, the patient underwent right anterior

temporal lobectomy and amygdalohippocampectomy within
the same year of initial evaluation. Pathological examination of
temporal lobe revealed microcolumnar neuronal alignment and
subpial gliosis in upper cortical layers. There was glial fibrillary acidic protein (GFAP)–positive gliosis and ectopic neurons in white matter and deep cortical layers. These findings
were found to be consistent with focal cortical dysplasia, type
Ia, according to ILAE 2011 classification. The patient had no
postoperative seizures during 2 years follow-up, even after
exposure to numerical stimuli. Postoperative EEG showed no
epileptiform discharges when the patient is still on carbamazepine and levetiracetam treatment. She also had no cognitive
problems on her postoperative neuropsychological tests.

Discussion
The aforementioned case experienced, till date, the first
reported type of reflex seizures triggered by visual, auditory, or
mental exposure to numbers. Besides the unique nature of the
triggering stimuli, association of seizures with a biopsy-proven
cortical dysplasia in right temporal lobe, successful preoperative demonstration of the ictal focus and cure of seizures following surgery are also of particular interest.
Diagnosis of reflex seizures was evident in this patient as all
seizures occurred shortly after being exposed to a multidigit
number. Seizures under monitoring took a little longer than
normal to start, probably because of the patient’s expectancy
for triggering stimuli, as reflex seizures are mainly triggered by
unexpected sensory stimuli.1 Seizure semiology strictly suggested right temporal lobe involvement, apart from the initial
aura of numbness in left arm, which would point to a parietal
lobe focus. MRI and ictal SPECT studies suggested a lesion in
right anterior temporal lobe. Invasive EEG study clearly demonstrated a right posterior mesial temporal ictal onset. Reflex activation of seizure focus would then be followed by prominent
epileptiform activity on dysplastic cortex and then seizure activity would rapidly spread to frontoparietal areas. Sensory symptoms at the beginning of seizures therefore would be related to

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Tezer et al

Figure 2. (A) The subdural strips and grids covered the right parietal, temporal (lateral, mesial, and basal), and frontal lobes. A, B, and C
were on the temporal lobe. D to G were on the parietal lobe. H was on the temporo-parietal and part of frontal region. I and J were on
part of frontal region. (B) Ictal EEG onset was beginning with attenuation and fast activity on right mesial temporal electrodes A, B, and C
(black arrow). High-pass filter, 70 Hz; low-pass filter, 0.1 Hz.

propagation of epileptic activity to parietal lobe. Besides prominent hyperperfusion in the right temporal lobe, slightly
increased perfusion in the frontal and parietal regions on ictal
brain SPECT supports this rapid propagation of epileptic activity. Right temporal lobectomy with amygdalohippocampectomy totally cured seizures and pathological examination
finally confirmed the diagnosis of cortical dysplasia.
Reflex seizures can be triggered by a variety of stimuli,
which can eventually be highly surprising. Triggers such as
flashing lights or visual patterns, somatosensory stimulation,
reading, eating, listening to music, thinking, playing chess,
exposure to hot water have been reported in the literature.1-6
Triggering stimuli in our case was highly exceptional. It could
not be regarded as a visual pattern–sensitive epilepsy because
exposure to single-digit numbers individually was not causing
seizures; the patient needed to see a multidigit number, like a
telephone number. Moreover, the patient was not dependent on
visual stimuli for seizures; hearing a number on TV or just trying to tell someone a phone number would always end up with
seizures. Although a calculation attempt would inevitably
result in a seizure, the patient did not need to make a mental
arithmetic operation to have a seizure, excluding calculationtriggered seizures for our case. These observations suggested
involvement of a higher cortical center as an association area
for numerical value representations. Stimulation of critical
amount of cortical tissue in this area either visually, auditory, or
mentally was initiating seizure activity. Numbers with higher
digits were probably stimulating a higher mass of hyperexcitable cortex, resulting in a greater probability of seizure, a common feature of reflex seizures.9,10
Cortical dysplasias can be epileptogenic, causing formation
of a high amount of abnormal connections among cortical and
subcortical areas.11 Stimulation of dysplastic or nearby cortex
via various afferent stimuli would therefore result in seizures.
There is highly limited experience reported in the literature for
reflex seizures associated with dysplasias and malformations.
Reflex seizures triggered by hot water exposure,7,12 eating,13
and thinking about a particular object14 have been associated

with dysplastic lesions. Typical for cortical dysplasia-related
seizures, our patient was refractory to antiepileptic drug therapy and excisional surgery was required for seizure relief.
Reflex seizures, especially when lesion associated, provide
an opportunity to increase our understanding of certain neurobiological processes. Dendritic rarefaction, decreased interneurons in the brain leading to inhibitory dysfunction has been
implicated as a mechanism for reflex seizures15; and erroneous
connectivity within dysplastic cortices may cause local imbalance of excitatory and inhibitory neuronal activity following
sensory activation. In our case, electrophysiological seizure
focus and anatomical lesion was in right temporal lobe. This
would suggest association of the nondominant temporal lobe
with higher numerical processing. Previously, a “triple-code”
model was suggested for number processing actions in the
brain.16 In this model, the numbers are predicted to be processed in 3 formats: a visual Arabic code, an analogue magnitude code, and a verbal code. The visual code involves the
perception of the presented string of digits for representation of
a numerical value and manipulation of numbers. Bilateral
activity in inferior ventral occipitotemporal areas are suggested
to take part in this code. Magnitude code establishes the knowledge for quantity on the represented number with activity in
bilateral inferior parietal cortices. Auditory verbal code manipulates verbal representations of numbers, stores arithmetic
facts, and takes part in calculation with involvement of dominant perisylvian areas. In our patient, the role of right temporal
lobe in triggered seizures, especially the temporal focus that
was demonstrated with cortical mapping studies would fit in
the visual code representation area in the triple-code model.
Ictal activity arising from occipital lobes may cause numerical
visual hallucinations17 and this seizure activity may spread to
temporal lobes17 via rich connections in between.18 Speculatively,
internal processing of numerical data within the occipital cortex
may be a rate-limiting step in our patient, causing a lag before
triggering the connections to the dysplastic temporal lobe. There
was no lesion or electrographic seizure activity in cortical areas
involved in the magnitude and verbal codes, and suitably,

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Clinical EEG and Neuroscience 

seizure triggering in our case did not require mental activity of
magnitude comparison or calculations.
It is difficult to explain how the patient’s seizures could be
triggered by auditory or mental stimuli besides visual ones, as it
is not known how the nonvisual stimuli would affect pathways
related to the visual number form. It would be useful to consider
that in epileptic patients, cortical lesions may shift the representative areas of cognitive functions and neurophysiological data
for number processing obtained from healthy controls might not
account for these patients in all cases. Accordingly, number processing skills were found to be affected in mesial temporal lobe
epilepsy patients involving both right and left temporal lobes.19
Conclusively, this unique case of “numerical” reflex seizures indicates that structural lesions in right anterior temporal
lobe should be investigated in similar patients and these cortical areas may play role in number processing.
Author Contributions
S.E.E, F.I.T, O.K and S.S were involved in the clinical care and investigative workup of the patient. K.K.O performed and evaluated the
MRI, E.L.E did the SPECT study and F.S. made the pathological diagnosis. S.E.E. drafted the manuscript, F.I.T and S.S. critically revised
the manuscript.

Declaration of Conflicting Interests
The author(s) declared no conflicts of interest with respect to the
research, authorship, and/or publication of this article.

Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.

Supplementary Material
Full-color figures are available online at http://eeg.sagepub.com

References
1. Ferlazzo E, Zifkin BG, Andermann E, Andermann F. Cortical
triggers in generalized reflex seizures and epilepsies. Brain.
2005;128(pt 4):700-710.
2. Goossens LA, Andermann F, Andermann E, Remillard GM.
Reflex seizures induced by calculation, card or board games, and
spatial tasks: a review of 25 patients and delineation of the epileptic syndrome. Neurology. 1990;40:1171-1176.

3. Pittau F, Tinuper P, Bisulli F, et al. Videopolygraphic and functional MRI study of musicogenic epilepsy. A case report and literature review. Epilepsy Behav. 2008;13:685-692.
4. Striano S, Coppola A, del Gaudio L, Striano P. Reflex seizures
and reflex epilepsies: old models for understanding mechanisms
of epileptogenesis. Epilepsy Res. 2012;100:1-11.
5. Zifkin BG, Inoue Y. Visual reflex seizures induced by complex
stimuli. Epilepsia. 2004;45(suppl 1):27-29.
6. Rey M, Pelletier J, Dalecky A, et al. Reflex epilepsy with seizures
induced by mental calculation, playing chess and Scrabble [in
French]. Rev Neurol (Paris). 1996;152:116-120.
7. Tezer FI, Ertas N, Yalcin D, Saygi S. Hot water epilepsy with
cerebral lesion: a report of five cases with cranial MRI findings.
Epilepsy Behav. 2006;8:672-676.
8. Marta Moreno J, Mauri Llerda JA, Pascual Millán LF, Morales
Asín F. Reflex epileptic seizures induced by calculation, card or
board games and spatio-visual abilities [in Spanish]. Neurologia.
1992;7:41-42.
9. Palmini A, Gambardella A, Andermann F, et al. Intrinsic epileptogenicity of human dysplastic cortex as suggested by corticography and surgical results. Ann Neurol. 1995;37:476-487.
10. Binnie CD. Evidence of reflex epilepsy on functional systems in
the brain and “generalised” epilepsy. In: Wolf P, Inoue Y, Zifkin
B, eds. Reflex Epilepsies. Vol 19. Paris, France: John Libbey
Eurotext; 2004:7-14.
11. Palmini A. Electrophysiology of the focal cortical dysplasias.
Epilepsia. 2010;51(suppl 1):23-26.
12. Grosso S, Farnetani MA, Francione S, et al. Hot water epilepsy
and focal malformation of the parietal cortex development. Brain
Dev. 2004;26:490-493.
13. Labate A, Colosimo E, Gambardella A, et al. Reflex periodic
spasms induced by eating. Brain Dev. 2006;28:170-174.
14. Martinez O, Reisin R, Andermann F, Zifkin BG, Sevlever G.
Evidence for reflex activation of experiential complex partial seizures. Neurology. 2001;56:121-123.
15. Ferlazzo E, Adjien CK, Guerrini R, et al. Lennox-Gastaut syndrome with late-onset and prominent reflex seizures in trisomy 21
patients. Epilepsia. 2009;50:1587-1595.
16. Dehaene S, Cohen L. Towards an anatomical and functional model
of number processing. Mathematical Cogn. 1995;1:83-120.
17. Gastaut H, Zifkin BG. Ictal visual hallucinations of numerals.
Neurology. 1984;34:950-953.
18. Fujita I. The inferior temporal cortex: architecture, computation,
and representation. J Neurocytol. 2002;31:359-371.
19. Delazer M, Gasperi A, Bartha L, Trinka E, Benke T. Number processing in temporal lobe epilepsy. J Neurol Neurosurg Psychiatry.
2004;75:901-903.

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