NEW YORK -- Television and computer screens update images many times a second. While we may not be conscious of this "screen flicker," new research suggests that certain regions of our brains register these tiny image alterations.

The fact that we see the image as steady, and not oscillating, suggests that the brain regions that acknowledge screen flicker do not send that information to the rest of the brain.

"We hypothesize that the brain operates as a kind of filter for this excess of useless visual information," Drs. Pierre Krolak-Salmon and Marie-Anne Henaff of the Institut National de la Sante et de la Recherche Medicale Unite in Lyon, France, told Reuters Health in an E-mail interview.

The researchers noted that these findings offer a reason why some people with epilepsy have seizures while watching television or playing video games. "For this particular population of patients, computer screen flicker may represent a danger," they said. "Our findings emphasize that the brain processes this kind of very rapid unperceived stimulus, which may represent an overload for the nervous system."

And even people without epilepsy may experience problems as a result of screen flicker, Krolak-Salmon and Henaff continued.

"Computer screen flicker, when its frequency is low, may induce headache, eyestrain and glare," they explained, especially in people who are prone to headaches.

Previous research has suggested that people have less discomfort with higher frequencies -- such as 100Hz -- but most televisions in France flicker at around 50Hz, and computer screens at 60Hz to 85Hz, the authors explained.

But the authors cautioned that people should not feel that their screens pose serious health risks. "We do not think that people watching a computer screen all day long have a real health risk," they said. "However, photosensitive epileptic patients and people subject to migraines must be careful."

Experts have shown that seizures can be triggered by lights flashing or flickering at certain frequencies, or the geometric patterns in the video display of computer games. This condition, known as photosensitive epilepsy, is more common in children and adolescents and becomes less frequent with age.

The current study findings, reported in the January issue of ****Annals of Neurology****, are based on results from three patients with epilepsy that did not respond to drugs and were considering surgery to remove the portion of their brain inducing seizures.

Before surgery, doctors implanted electrodes in their brains to home in on the specific area originating the seizures, and monitored the activity in these brain regions for two weeks.

The authors found that patients showed increased brain activity when exposed to screen flicker in regions of the brain involved in processing visual information, indicating that portions of their brains were "seeing" screen flicker.

People can sidestep side effects of screen flicker by watching plasma screens, which have no flicker, Krolak-Salmon and Henaff said. Krolak-Salmon also holds a position at the Hopital Neurologique, also in Lyon. (Reuters)