By Pat Hagan

Migraines affect one in 10 people

The blinding headaches can be caused by a wide range of triggers, from tiredness or stress to certain foods and drinks - such as cheese and alcohol.

But one of the least understood aspects of the disorder is why some sufferers develop an attack after seeing certain patterns - such as stripes.

Now a team of psychologists at Birkbeck College in London are beginning a two-year study to explore exactly what happens within the brain and the visual system when the eyes focus on these patterns and, crucially, how that culminates in an agonising headache.

They hope their research will lead to new guidelines that may minimise the risk of exposure to these patterns in the workplace and at home.

"It is thought that around 40% to 50% of migraine sufferers have visual triggers," says Dr Alex Shepherd, who is leading the study funded by Action Medical Research and the Migraine Action Association.

"Some are very aware that they have a visual trigger but others are not. This can be because the effects are not always instantaneous - an attack can be triggered several hours later."

Common condition

It is estimated that migraine afflicts around six million people in the UK, or about 10% of the entire population.

If we can find out more about these visual triggers, then we can write guidelines for sufferers to try and minimise their exposure to them. Dr Alex Shepherd

Women tend to suffer most, with one in four affected, compared to one in 12 men.

The majority of sufferers have what's called common migraine - or migraine without aura.

This is a severe, throbbing headache, usually on one side, accompanied by loss of appetite, nausea, vomiting and constipation or diarrhoea.

The more serious form is classical migraine - or migraine with aura - and involves visual disturbances such as flashing lights, zigzag lines, blind spots and tingling limbs.

The average length of a migraine attack is 22 hours and sufferers can be left washed out for days afterwards.

For years, the condition has been regarded as a trivial problem with no lasting damage.

Stroke risk

But a recent Dutch study found evidence that migraine damaged part of the brain called the cerebellum and increased the risk of a stroke.

Regular sufferers know to avoid the foods or stress that could set off another painful attack.

But pinpointing what the visual trigger is can be much more difficult.

Dr Shepherd believes certain types of patterns, which are known to make nerve cells within the visual system highly excitable, are probably to be blame.

"There are some very potent patterns for nerve cells in the visual system. For example, there are cells in the visual cortex - a part of the brain that processes vision - that like stripes.

"Different cells like different widths of stripes, some cells like different orientations and others like motion."

In migraine sufferers, Dr Shepherd says, the stimulation of these cells somehow upsets the balance.

"If you look at a certain pattern - such as vertical stripes - you'll be giving those cells that respond to vertical stripes exactly what they like.

"They will respond to the pattern and your visual cortex will 'light up' with activity as the neurons do their job.

"But this intense activity is unnatural - it upsets the normal balance and tends to result in vivid visual illusions."

New guidelines

Dr Shepherd has devised a series of experiments designed to unravel the process by which looking at patterns leads to blinding pain.

Her hope is that the project will result in guidelines for migraine sufferers to help them reduce the number of attacks they experience.

"These may spell out potential triggers - whether they be TV displays or computer monitors.

"If we can find out more about these visual triggers, then we can write guidelines for sufferers to try and minimise their exposure to them," she says.

"It's also possible that new treatments will come out of this research."

Professor Peter Goadsby, from the headache and migraine group at the Institute of Neurology in London, said it was feasible that reducing exposure to visual triggers may lead to fewer attacks.

"Triggers are very individual and it is possible that the frequency (of exposure) may be important.

"I think many people not even know they have a visual trigger. I am not sure there are any data but it is reasonable to say it is not uncommon."