Epilepsy is one of the most common neurological diseases in the
world. According to the World Health Organization (WHO), almost 50
million people worldwide suffer from it and 30% do not respond to
The disorder is characterized by epileptic seizures -
episodes of the uncontrolled, synchronized activity of neurons that can
lead to loss of consciousness and other serious impairments of brain
‘Visual stimulation with frequencies close to alpha rhythm may interfere with the natural alpha activity prevailing in the visual cortex leading to an increase of amplitude of the discharges and consequently to epileptic seizures.’
Why does exposure to rhythmic stimulation at certain frequencies facilitate the occurrence of epileptic seizures?
In 1997, flickering patterns in an episode of the series Pokémon
triggered epileptic seizures in nearly 700 Japanese children. These
spontaneous outbreaks in apparently healthy children were linked to
so-called "photosensitive epilepsy", a type of epilepsy in which
seizures are the result of certain visual stimuli.
Now researchers at Pompeu Fabra University (UPF), Polytechnic
University of Catalonia (UPC) and the University of Exeter (UoE, UK)
propose an explanation for the occurrence of epileptic seizures as a
result of the exposure to certain stimuli.
The study has been published in the journal NeuroImage
Considering the brain as a dynamic system allows engaging tools from
engineering and physics in order to find out what factors lead to the
occurrence of these highly synchronized epileptic discharges. The
research by UPF, UPC and UoE has used a computational model of a
cortical column - a putative basic functional unit of the cerebral
cortex - to show that neuronal tissue displays epileptic-like activity
when exposed to enhanced stimulation of certain frequencies. This
increase may be due to the brain's own activity or a consequence of
external stimulation, such as the flickering in the Pokémon cartoon.
According to the research results, this behavior stems from dynamic
properties of the neuronal tissue, such as an ability to undergo
resonance. Visual stimulation with frequencies close to alpha rhythm
(which was the case of the flickering in Pokémon) may interfere with the
natural alpha activity prevailing in the visual cortex leading to an
increase of amplitude of the discharges and consequently to epileptic
seizures. This resonance phenomenon can be compared to what happens when
we push a swinging child. If we push it at the right moment, with a
frequency equal to the swinging frequency, it will swing further and
further and eventually may fall from the swing.
This fall is an analogy to an epileptic crisis that may occur in the
brain due to stimulation with a certain frequency. In the Pokémon
series, the lights flashed at a frequency of 12Hz.
"The alpha rhythm of the brain is 8-12Hz and the cartoons were
showing exactly the alpha frequency of 12Hz. This phenomenon coincides
with the results of our research", says the author of the study, Maciej
Thus, a purely dynamic scenario can explain the susceptibility to
driving with delta and theta rhythms, as well as a lack of
susceptibility to very fast or very slow stimulation. The researchers
showed how these phenomena manifest in the presence of random driving,
which mimics the ongoing stimulation of a cortical column more
faithfully than the periodic one.
"This research provides further insight into ways that communication
within brain networks can possibly lead to the occurrence of seizures"
comments Marc Goodfellow, senior lecturer in Mathematics at the
University of Exeter and leader of the study.
According to Jordi Garcia-Ojalvo, group leader of the Dynamical
Systems Biology Lab at UPF and collaborator in the study, "this work
shows that the temporal characteristics of the random activity of the
brain can have profound effects on its behaviour".
"In order to develop new alternative kinds of epilepsy treatment we
need to understand more about the mechanisms underlying this disease",
adds Jedynak, researcher at the same lab and the leading author of the
article. "Our findings help to elucidate mechanisms of the generation
and spreading of epileptic seizures in the brain. In the future they may
improve the methodology of computational modelling aimed at devising
tools for epilepsy treatment".