What does brushing your teeth has to do with seizures?

The breakthrough will help neurologists understand how the most common triggers -- sleep and stress -- can spark fits.

"The tooth-brushing trigger is very, very unusual, but now we understand what's behind it the implications are great," said Dr Wendy D'Souza, leader of research published yesterday in US journal Neurology.

The team from St Vincent's Hospital, Melbourne, investigated three middle-aged people who had jerking or twitching-type seizures when brushing certain areas of their mouth.

Using head scans, researchers discovered all three patients had a lesion in the somato-sensory part of the brain, which is close to the hand and speech motor areas.

"The rhythmic act of brushing teeth may excite an already overly excitable area of the brain," Dr D'Souza said.

"It sends an electrical signal to a part of the brain which has this lesion and causes these jerking sorts of seizures."

He said this type was extremely rare, with less than a dozen reports worldwide, but had many similarities to the more common photosensitive type, triggered by strobe lights and moving patterns.

Specialists were able to medicate these epileptics with a specific dose, which overrides the tooth-brushing trigger, and were now investigating the significance for other triggers.

About 2 per cent of Australians have the condition -- one half inherited and the other sparked by a mark or lesion somewhere in the brain.