Scientists may be a step closer to uncovering the cause of certain types of debilitating migraine headaches.
A French team observed activation in the hypothalamus region of the brain as sufferers had a migraine attack.
The hypothalamus has long been suspected as it regulates physiological responses to factors known to trigger headaches, such as hunger.
It is hoped the discovery, featured in the journal Headache, could lead to new treatments.
The researchers, from Rangueil Hospital, used a technique called Positron Emission Tomography (PET), which contrasts functional activity within the brain, on seven patients with migraine without aura, the most common type of migraine.
Previously, activation in the brain stem and midbrain, and a thickening in some areas of the cortex were seen in migraine sufferers.
The present study may have seen a more detailed pathogenesis of the condition for two reasons.
First, timing was crucial: to capture an attack as it happened, patients rushed to hospital without self-medicating, arriving on average around three hours after the onset of the migraine.
Second, the observed headaches were spontaneous, and not chemically induced as in other laboratory studies.
Lead researcher Dr Marie Denuelle said: "When you induce the attack you miss the hypothalamic activation.
"We suspect the hypothalamus may play a role in the start of the migraine attack.
"But to prove it we would need to do similar study before the start of an attack."
Dr Andrew Dowson, director of headache services at Kings College Hospital, London, said: "It has been suggested for many years that the hypothalamus is involved in the early stages of migraine attacks.
"But there are other factors involved in the early generation of headache."
Activation of the hypothalamus had previously only been seen in cluster headache, a different and altogether more crippling condition.
Cluster headache sufferers experience headaches on a regular basis: for certain months of the year in the episodic form, or every day at regular intervals in the chronic form.
So debilitating can the attacks be that they have been dubbed "suicide headaches" because some sufferers have taken their own lives.
The new evidence for hypothalamic activation in migraine may explain why some migraine drugs, particularly the triptans, can sometimes be effective at aborting a cluster headache attack.
However, Professor Peter Goadsby, of the Insitute of Neurology at University College London, said there were distinct clinical and physiological differences between cluster headache and migraine.
He said: "The area [of the hypothalamus] reported as activated in migraine is about 10mm more anterior than the cluster headache area.
"The hypothalamus is not one thing but a collection of discrete neurons."
Professor Goadsby said a cascade of changes in the brain seemed to cause the migraine problem.
"It's easy to think that migraine is a specific brain disorder, but it is a series of systems that go wrong - a system disorder.
"There is no single holy grail. Multiple structures are involved."