Workers who report that their office regularly gives them a migraine might not be victims of fragrances, chemicals or other components of “sick building syndrome”.
Their headaches and nausea might instead be triggered by patterns of light and shadow seen through the window or projected onto walls. For some people, these accidental expressions of architecture might even trigger a seizure.
Research published in Current Biology has uncovered a link between certain types of still images and epileptic episodes. It is tied up with a mysterious neurological function known as gamma oscillation – rhythmic neural activity producing high-frequency (30-80 Hz) brainwaves. While the function of these brainwaves is unknown, some scientists believe it is related to consciousness and visual perception.
Using scalp electroencephalograms, Dora Hermes of the University Medical Centre Utrecht, in the Netherlands, and colleagues discovered certain types of still images – such as black-and-white gratings – are associated with increased levels of gamma oscillation in the brain. Other pictures – of soft fluffy clouds, for instance – are not.
Gamma oscillations are also strongly linked with images, still or moving, that trigger seizures in people with photosensitive epilepsy.
Yet while the link between brain activity and image types is strongly demonstrated in the research, the significance of the finding remains unclear.
This is primarily because there is little consensus among neuroscientists about what gamma oscillation brainwaves actually do. Theories range from a critical involvement in thought processes to a useless by-product of other neurological actions.
“Some scientists argue that these oscillations are hugely important and essential for awareness, attention, and neuronal communication,” Hermes says, “while others say that they are more likely a by-product of normal neuronal processing, like the exhaust coming out of a car.”
The by-product theory is partly bolstered by the new research, because evidence suggests the oscillations arise only in response to certain images, rather than all images. The researchers also discovered that the strong oscillations linked to grid patterns could be reduced by softening the contrast of the image, by dilating focus or adding colours.
However, researchers also noted that no other forms of brain activity correlate with images that trigger seizures, indicating that whatever the eventual function of the oscillations turns out to be, it might hold the key to an eventual epilepsy treatment.
“What we distinguish in this proposal is that the link between images that trigger photosensitive epilepsy and normal brain activity is particular to gamma oscillations, and not to other forms or neuronal responses,” says Hermes.
The fact that certain types of moving images can trigger epilepsy has long been known, even if sometimes that knowledge is poorly applied. In 1997 the airing of an episode of the Pokemon cartoon series in Japan induced seizures in almost 700 viewers. The episode, ‘Electric Soldier Porygon’, has been banned from rebroadcast.
Hermes’ work with static images, however, suggests a possible link between seizure (and, less seriously, migraine) and high-contrast repetitive grids created unintentionally.
“Our findings imply that in designing buildings it may be important to avoid the types of visual patterns that can activate this circuit and cause discomfort, migraines, or seizures,” Hermes says. “Even perfectly healthy people may feel modest discomfort from the images.”