A rash of epileptic seizures triggered by a television cartoon has pinpointed a new type of epilepsy, according to a report in this month's Annals of Neurology, the scientific journal of the American Neurological Association and the Child Neurology Society.
One evening in Japan in 1997, at precisely 6:50 in the evening, 685 people, most of them children, simultaneously suffered epileptic seizures. The culprit was not difficult to identify: all were watching the popular animated TV show, "Pocket Monsters."
Japanese researchers have now found evidence that the seizures were provoked by rapid changes of blue and red in the background of the cartoons.
Flickering lights such as strobe lights or even the images on a television or video screen are well known as triggers for epileptic seizures. Patients who experience such seizures are said to suffer from photosensitive epilepsy.
Rapid light/dark changes or alternating high-contrast patterns cause nerve cells in the brain to fire electrical impulses more rapidly than usual. In people with photosensitive epilepsy, the resulting "electrical storm" in the brain can lead to muscular convulsions or loss of consciousness.
Although photosensitive epilepsy is not a new phenomenon, the events in Japan appear to be unprecedented.
"This may be the world's largest simultaneous occurrence of photosensitive symptoms in children provoked by viewing a TV program. Therefore, the seizures were considered to be triggered by a single uniform visual stimulus," said Shozo Tobimatsu, M.D., a neurologist at Kyushu University in Japan and one of the authors of the article.
Tobimatsu and his colleagues studied 4 boys who had suffered seizures during the cartoon. Like many others, they were not known to suffer from epilepsy, although some had a family history of epilepsy.
The researchers measured brain wave responses as the boys watched the cartoon in color or in black and white. They found that only 2 of the boys were sensitive to light/dark changes, but that all 4 boys had abnormal, epilepsy-like brain changes when exposed to the color version of the cartoon.
Because the cartoon had a flickering blue and red background, the researchers also showed the boys rapidly alternating blue and red images.
"Rapid color changes between blue and red in the cartoon were clearly the most important factor compared with color changes of other kinds and flickering light," said Tobimatsu.
These results, combined with a report last year of color-induced seizures in Great Britain, led the Japanese team to propose a new subcategory of photosensitive epilepsy called chromatic sensitive epilepsy.
Other authors of the report were You Min Zhang, M.D., and Motohiro Kato, M.D., also of Kyushu University; and Yasuko Tomoda, M.D., and Akihisa Mitsudome, M.D., of Fukuoka University.
Materials provided by American Neurological Association. Note: Content may be edited for style and length.
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