This Post Will Not Cause a Seizure

by Michael Grisafe on November 2, 2012


Image courtesy of Simon Howden

I promise.

After my last post a reader informed me that an animated graphic included in my blog may have the potential to cause seizures. This is bad. Very bad. I don’t like people to have seizures as a consequence of reading my blogs. I’m just old-fashioned that way.

Killer Mice

A still version of the “seizure mice.”
Original pictures from Microsoft Clip Art.

The offending blog contained a poorly constructed animation of mice dancing around a pumpkin, and I considered it a rather sad thing that such a playful, whimsical bit of fluff might cause a medical problem.

But it did make me think: just how common are seizures caused by visual phenomena? I mean, are my dancing mice a real health risk or, in the words of a friend, are they just “an annoying Internet gimmick desperately waving its hands for attention”?

It was time for some detective work.

I scoured the web and came up with the following:

 Photosensitive Epilepsy (PSE)

About 3 million individuals across the United States are affected by epilepsy and seizures.1 “Symptomatic seizures” are caused by identifiable diseases or brain abnormalities. Known causes for seizures include genetic defects, tumors, infections, head trauma, stroke, Alzheimer’s disease, and a number of other medical concerns. Medical professionals label a seizure as “cryptogenic” if its cause cannot be found.

In a special type of epilepsy called “Photosensitive Epilepsy” (PSE) individuals exposed to visual stimuli, such as a flashing light or changing color patterns, can lapse into a seizure. With the prevalence of TVs, computer monitors, and other electronic screens that dominate modern society, individuals with PSE must be especially careful to avoid seizure-inducing stimuli.

 How Common is Photosensitive Epilepsy (PSE)?

About 1 in 4,000 individuals ages 5-24 are affected by PSE. Clinical PSE is found in about 2% of individuals of all ages who have seizures.2

What Causes PSE?

Researchers are divided on the specific cause of PSE, but it is characterized by abnormal sensitivity of the brain to visual stimulation.3

 Who is affected?

Video Game Boy

Image courtesy of Poonsap /

PSE appears to be transmitted genetically, so if a parent is affected by the disorder, their children are more likely to have it as well.4 It has an early onset between 2 to 18 years, with a peak between 12 to 13 years.5Two-thirds of those affected are females; however many studies reported a higher incidence of photosensitive seizures in young males.

One study explained this discrepancy between diagnosis and disease by citing the larger proportion of young males playing video games with PSE inducing stimuli.6 However, this study, like many others of its kind, was done in the ‘90’s and early 2000’s. In the intervening decade female use of video games has skyrocketed7 (as fellow MTSG blogger Shara Evans can attest), so it would be interesting to see if this epilepsy pattern has evened out in a future study.

 Visual Factors that Make Seizures More Likely for Those with Photosensitive Epilepsy


Studies have found that brighter stimuli are more likely to induce seizures. Sudden changes in the luminance of a screen also contribute to seizure potential. Because of this, television broadcast guidelines include specifications for changes in screen luminance during programming.


Some seizures can be triggered by viewing patterns. Black white stripes are the most common offender, and when combined in a vibrating or flickering pattern, the incidence of seizures increases. Although stripes occur often in everyday life, viewing them on a video screen appears to increase their potential to cause seizures.

 Flash Frequency

The flash, or flicker frequency, is the most important factor in determining photosensitivity to video screens. Flash frequencies with the highest likelihood of causing a seizure occur at both 9-18 flashes per second and 50 flashes per second.


Image courtesy of imagerymajestic /

In the early ‘90’s researchers in Great Britain began investigating seizures that had taken place among children playing the video game “Super Mario World.” 9They found that the bright backgrounds and flashing patterns that the game contained lent themselves to seizures among children susceptible to PSE. In addition, children playing on a 50 Hertz television experienced a greater likelihood of a seizure (the scientific measurement of “Hertz” refers to frequency per second).

This susceptibility to flash frequency also extends beyond video monitors to phenomena present in everyday life. For instance, one case study reported that a man being transported by a helicopter after a medical emergency experienced a seizure in response to the flashing light and dark pattern created by the helicopter blades and sunlight.10


The length that an individual is exposed to stimuli also influences their risk of having a seizure. In other words, a child with PSE is much more likely to have a seizure after five minutes of watching flashing lights versus one.


Flickering red or red and blue colors have been found to cause seizures in many PSE individuals. One of the most famous examples of this seizure-inducing phenomena occurred during the Japanese airing of a Pokémon cartoon on December 17, 1997.11 In the cartoon, an explosion hits a character, followed by several seconds of flashing red and blue. To make matters worse for those susceptible to PSE, the flashes occurred at 12 flashes a second.


Flashing police lights have not been shown to cause seizures. Image courtesy of Microsoft Clip Art.

After this cartoon aired, 682 people experienced seizures and were taken to hospitals. It was not a good day to “Catch ‘Em All.”

On a side note, the flashing red and blue police lights on a police car have not been shown to be seizure-inducing.12 So while there are plenty of reasons to be worried when you see the red and blues flashing in your rear-view mirror, having a seizure is not one of them.

 Cognitive Engagement

Research has found that increasing cognitive demands on PSE-sensitive individuals exposed to one of the stimulus described above increases their risk for a seizure. For instance, individuals playing puzzle games projected on a 50 Hertz screen displayed a high likelihood of having a seizure. In addition, the “Super Mario World” study cited above found that individuals actively playing the game were much more likely to have a seizure than those passively watching the video game being played by someone else.13

 Do My Dancing Mice Pass the Epilepsy Test?

At the start of this article I discussed the annoying/fancifully charming dancing mice graphic that I used in my last blog. So, after all my research, are they really dangerous to individuals susceptible to PSE?

Well, let’s check it out.

CLICK HERE to view the animated mice graphic (just in case it somehow does induce epilepsy, I’m not putting it in this blog!).


Image courtesy of Microsoft Clip Art

First, the overall brightness of the graphic never changes, and there are no stripes or flashing shapes occurring for any duration. The frolicking mice themselves move at a frequency of one frame per second (far below the offensive 9 flashes per second threshold), and there is no red or blue present. Aside from my sorry attempt at transcendent animation, I have to admit it’s really minimally cognitively engaging (unless you are really, really into dancing mice). I suppose that duration could be an issue if you stared the graphic for several minutes, but I think most people scan down the page (or immediately click off my blog!).

Now, I’m not a physician, but according to the guidelines presented in the research, it would appear that the dancing mice are kind of…well…OK in a non-seizure-inducing sort of way.

As for charges that it’s gimmicky, shticky, and ultimately sort of annoying, I really can’t defend it.

PS If you are concerned that your website might be seizure inducing, check out this free, downloadable “Photosensitive Epilepsy Tool” (PEAT): Developed by the University of Wisconsin’s Trace Center, it analyzes websites using many of the criterion listed above to help developers identify potentially problematic animations and stimuli.

electric head

Image courtesy of Salvatore Vuono /

1The Epilepsy Foundation.  (n.d.).  Incidence and Prevalence.  Retrieved from
2Epilepsy Therapy Project. (n.d.). Photosensitive Epilipsy. Retrieved from
3Tauer, U., Lorenz, S., Lenzen, K. P., Heils, A., Muhle, H., Gresch, M., Neubauer, B. a, et al. (2005). Genetic dissection of photosensitivity and its relation to idiopathic generalized epilepsy. Annals of neurology, 57(6), 866–73. doi:10.1002/ana.20500
5Epilepsy Therapy Project. (n.d.). Photosensitive Epilipsy. Retrieved from
6Trenite, D.G.A, da Silva, A.M., et al. (2002). Video games are exciting: A European study of video game-induced seizures and epilepsy. Epileptic Disorders. 4(2). 121-8. Retrieved from
7Williams, D., Consalvo, M., Caplan, S. & Yee, N. (2009). Looking for gender: gender roles and behaviors among online gamers. Retrieved from
8Zifkin, B. G., & Inoue, Y. (2004). Visual reflex seizures induced by complex stimuli. Epilepsia, 45 Suppl 1, 27–9. Retrieved from
9Trenite, D.G.A, da Silva, A.M., et al. (2002). Video games are exciting: a European study of video game-induced seizures and epilepsy. Epileptic Disorders. 4(2). 121-8. Retrieved from
10Cushman, J. T., & Floccare, D. J. (n.d.). Flicker illness: an underrecognized but preventable complication of helicopter transport. Prehospital emergency care : official journal of the National Association of EMS Physicians and the National Association of State EMS Directors, 11(1), 85–8. doi:10.1080/10903120601021457
11Wikipedia. (n.d.). Dennō Senshi Porygon. Retrieved from
12Vainstein, G., Yoffe, V., & Gadoth, N. (2000). Can police car colored flash light induce encephalographic discharges and seizures? Croatian medical journal, 41(3), 319–22. Retrieved from
13Trenite, D.G.A, da Silva, A.M., et al. (2002). Video games are exciting: A European study of video game-induced seizures and epilepsy. Epileptic Disorders. 4(2). 121-8. Retrieved from

[Update 11/05/2012:  As per Elizabeth’s comment below, I have added a caption on the police light photo to make it more apparent that there is no evidence that they cause seizures.]

Margaret November 2, 2012 at 1:21 pm

This was especially interesting to me as I have had many students in the past couple of years contact me about making sure that my lectures are non seizure inducing.
The first time I was probably as surprised as you were. Good research.

Michael Grisafe November 5, 2012 at 9:26 am

Hi Margaret,

That’s interesting. Does it seem to be on a regular basis? Most of the research seemed to indicate that Photosensitive Epilepsy (PSE) has a fairly low prevalence in the population. What kinds of graphics or animation do these individuals say tends to trigger their seizures? Are there any things that tend to repeatedly come up? If you do have a graphic that you are wondering about, the PEAT tool above seems to work pretty well. Thanks, as always, for reading!

Margaret November 5, 2012 at 9:56 pm

I have recently been teaching a class on the mathematics of fine arts. The student came to me came before class, because they were worried I might use a lot of computer graphics to show examples.
I am sort of old school (ie… I make them do a lot of constructions by hand) in my teaching so, I did not need to worry about it. In my on-line math class, I just contacted the company that ran the program to make sure that they had checked for that possibility.
I never heard a complaint from the students later, so I must have made my lectures seizure free. :)

Michael Soso PhD MD November 2, 2012 at 1:39 pm

I agree that your dancing mice are unlikely to be epileptogenic.

Michael Grisafe November 5, 2012 at 9:28 am

Excellent! Have you had experience in treating individuals with PSE? I’m just curious to see in your experience people report as their triggers.

Jennifer November 2, 2012 at 2:59 pm

on a personal note, i have a friend who is very sensitive to animated graphics, and has had many setbacks before she stopped trusting graphics on the internet. (every time she had a seizure, she had to stop driving till she was seizure-free for 6 months.) i think it’s best not to risk it and avoid animated graphics and flashy animations as a general rule. Not only can they be unsafe (even with the stats what they are, there can always be someone more sensitive than the research predicts, and I have heard anecdotal reports of folks having seizures after catching sight of flashing text or strangely repetitive graphics), but they’re a little outdated and unattractive. I tend to be mobile when I’m surfing a lot of the time, and animated graphics just slow my device down, or don’t show up at all, anyway.

On a professional note, I think it’s awesome that you took constructive criticism and turned it into a teachable moment for a much wider audience. You educated people about a topic that’s usually relegated to bad (and ableist) jokes or dismissed entirely, and raised awareness about epilepsy in general. Thanks for that.

The bold headlines and short descriptions make the post a good reference with helpful information blurbs that are easy to scan and digest. Nice job!

Michael Grisafe November 5, 2012 at 9:34 am

Thanks for the feedback, Jennifer! I’m glad you liked the post. To deal with her PSE, does your friend disable all photos and graphics on her web browser? It must be very difficult for these individuals and I was wondering if many of them simply resort to text only web-browsing. Writing this post made me realize just how many factors these individuals have to consider when anticipating, and planning to avoid, certain visual stimuli.

Elizabeth November 5, 2012 at 12:07 am

Every time that I walk through the tunnel at the Detroit airport, I wonder to myself how it has not given someone a seizure yet. [update: after Googling “detroit airport tunnel seizure” I have learned that there is a button at either end of the tunnel that anyone can press to suspend the light and music show for 5 minutes]

While I am certainly not a blogging professional (just Ali’s friend from high school), I want to suggest that you give captions to your pictures that explain a little more about why you included the picture. Not everyone will take the time to read every word of the post which causes some of the pictures do not make sense and/or are misleading. Example of what the person skimming the post sees:

section header: Color
first sentence: Flickering red or red and blue colors have been found to cause seizures in many PSE individuals.
photo: red and blue police car lights

When you read the rest of the section, you come to learn that police car lights do NOT cause seizures, which is a very very important point! Since the purpose of the blog is to provide accurate public health knowledge, you have to be careful that readers do not leave confused. The picture captions can be a great place to include your key points: “While red and blue lights have been shown to be seizure-inducing, lights on police cars do not have that effect.”

Otherwise, this was a very interesting and informative post!

Michael Grisafe November 5, 2012 at 9:42 am

Hi Elizabeth,

Those are excellent points! I was actually wondering how that police graphic would be taken given the context of the heading. If you were confused, I’m sure many others were as well. I agree that given its current section heading, it is very misleading (as per your suggestion, I am actually adding a caption to this particular graphic).

Sometimes I forget that most people skim over blogs on the web, so that creating a coherent story using section headings and pictures is absolutely critical. Thanks for reminding me!

JeremyPaul Wachs May 30, 2013 at 2:28 am

The REWARDS (an internet outfit that does surveys and other slimy chores) has graphics that are so annoying I am in fear of seizure.

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