A US study has found that the cortex area of the brain is thicker in people who have migraines compared to those who do not. The researchers do not know whether the difference causes the migraine or having migraine over the years has led to the difference in brain structure.

The study is published in the 20th November online issue of the journal Neurology and is the work of Dr Nouchine Hadjikhani, of The Martinos Center for Biomedical Imaging at Massachusetts General Hospital in Charlestown, Massachusetts, and colleagues.

Dr Hadjikhani and colleagues compared 24 people who suffered from migraine with 12 people who did not, and found that the somatosensory cortex (SSC) area of the brain of those with migraine was on average 21 percent thicker.

"Repeated migraine attacks may lead to, or be the result of, these structural changes in the brain," said Hadjikhani in a prepared statement.

"Most of these people had been suffering from migraines since childhood, so the long-term overstimulation of the sensory fields in the cortex could explain these changes," she added.

Alternatively, the researchers suggested it could be that people who develop migraines are naturally more sensitive to stimulation.

Using magnetic resonance imaging (MRI), the researchers had already discovered there were structural differences between the brains of people with migraine and people without. In this new research they measured group and individual differences in cortical thickness in migraine patients who were matched for age and sex with healthy subjects.

The results showed that the people who suffered from migraine had on average 21 per cent thicker SSCs than those who did not, and the most significant differences in cortical thickness were in what is known as the caudal (tail) SSC, where sensations from the trigeminal area, the head and face, are processed.

Most of the migraine patients had been getting migraines since they were children. This might suggest that long term stimulation of the cortex over such a long period could lead to structural changes, said Hadjikhani.

On the other hand, it could also be that their brain's structure changed progressively for some other reason and this led to the headaches.

However, regardless of the cause and effect question, the results show that the sensory areas of the brain are important components in migraine.

"This may explain why people with migraines often also have other pain disorders such as back pain, jaw pain, and other sensory problems such as allodynia, where the skin becomes so sensitive that even a gentle breeze can be painful," added Hadjikhani.

The researchers concluded that the SSC plays a key role in the processing of "noxious and nonnoxious" somatosensory signals, and that:

"Thickening in the SSC is in line with diffusional abnormalities observed in the subcortical trigeminal somatosensory pathway of the same migraine cohort in a previous study. Repetitive migraine attacks may lead to, or be the result of, neuroplastic changes in cortical and subcortical structures of the trigeminal somatosensory system."

Their next step is to perform a larger study to find out whether the migraines cause the structural changes or vice versa, by studying MRIs of children who are at high risk of developing migraines because one of their biological parents had them.

Other studies have also revealed the cortex of people who have certain conditions is different. For instance, people with multiple sclerosis and Alzheimer's disease have a thinner cortex. The area becomes thicker with extensive learning and motor training.

"Thickening in the somatosensory cortex of patients with migraine."
Alexandre F.M. DaSilva, Cristina Granziera, Josh Snyder, and Nouchine Hadjikhani.
Neurology, Nov 2007; 69: 1990 - 1995.
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Written by: Catharine Paddock