01 Jun Why Do Some Images Cause Seizures While Others Do Not?
Some images seem to cause seizures in people with photosensitive epilepsy but others do not. There is a major investigative study on the neurophysiological mechanism behind these seizures that is being conducted in universities around the globe.
The NINDS (National Institute of Neurological Disorders and Stroke) says epilepsy is the neurological disorder during which a group of neurons show abnormality and trigger a seizure. During this many brain cells may be sending signals all at the same time at the remarkable speed of 500 times a second.
Causes for photosensitive epilepsy
Flashing and flickering lights are a major cause of photosensitive epilepsy, such provocative visuals affect the person in stages. A Pokémon episode back in 1977 caused seizures in 685 people in Japan. The promotional video of the 2012 Olympics also caused a similar reaction and was soon taken off the website.
Static images are also known to cause seizures, as has been studied in detail by researchers from the field of neurophysiology. Dora Hermes from UMC (University Medical Center) in Nederland even brought out a publication on the subject.
The brain and gamma oscillations
The publication followed prior studies that talk about the role of gamma oscillation between the frequencies of 30-80 hertz being the cause of seizures.
The study was specific to static images and their spatial features like white and black stripes. The brain activity is a response to the repetitive pattern in such static images, causing migraines and headaches.
An electroencephalogram can measure gamma oscillations, and help in knowing more about their thought perception and the neural process that they cause. There are some researchers who believe that gamma oscillations are just the normal byproduct of neuronal processing, but others argue to say that they are immensely important, even essential for attention, neuronal communication, and awareness.
Grating patterns and seizures
Studies show that gamma oscillations appear in the brain upon seeing particular images so they cannot be essential or key to neural processing of the brain. Tests have shown that strong gamma oscillations are caused by images with grating patterns. Though this does not happen when a person sees images of clouds or nature or other calm images.
Researchers say that grating patterns are likely to be the cause of seizures and suggest ways to alter the images in order to avoid this.
- Reduce the size of the grating or pattern.
- Superimposing another second image on it to create a checkerboard or plaid or even adding noise effect to the pattern.
- Chromatic contrast alone is less provocative in comparison to square waves and sine.
Findings of the study
Further study, is still being conducted by Dora and team on brain patterns of people with and without photosensitivity. They are also working towards creating a model to know which natural scene is likely to provoke seizures.
As per Jonathan Winawer of the New York University (who is the Co-author of this study), there is a clear link between normal brain activity and the provocation of photosensitive epilepsy. This linkage is particular to gamma oscillations and does not extend to other neuronal responses.
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