In more than 40% of cases, however, the pain may be bilateral (both sides of the head), and neck pain is commonly associated with it. Bilateral pain is particularly common in those who have migraine without aura. Less commonly pain may occur primarily in the back or top of the head. The pain usually lasts 4 to 72 hours in adults; however, in young children frequently lasts less than 1 hour. The frequency of attacks is variable, from a few in a lifetime to several a week, with the average being about one a month.The pain is frequently accompanied by nausea, vomiting, sensitivity to light, sensitivity to sound, sensitivity to smells, fatigue and irritability. Many thus seek a dark and quiet room. In a basilar migraine, a migraine with neurological symptoms related to the brain stem or with neurological symptoms on both sides of the body, common effects include a sense of the world spinning, light-headedness, and confusion. Nausea occurs in almost 90% of people, and vomiting occurs in about one-third. Other symptoms may include blurred vision, nasal stuffiness, diarrhea, frequent urination, pallor, or sweating. Swelling or tenderness of the scalp may occur as can neck stiffness. Associated symptoms are less common in the elderly. Silent migraine
Sometimes, aura occurs without a subsequent headache. This is known in modern classification as a typical aura without headache, or acephalgic migraine in previous classification, or commonly as a silent migraine.
There are a number of explanations for its occurrence, including activation of NMDA receptors leading to calcium entering the cell. After the burst of activity, the blood flow to the cerebral cortex in the area affected is decreased for two to six hours. It is believed that when depolarization travels down the underside of the brain, nerves that sense pain in the head and neck are triggered. Pain
The exact mechanism of the head pain which occurs during a migraine episode is unknown. Some evidence supports a primary role for central nervous system structures (such as the brainstem and diencephalon), while other data support the role of peripheral activation (such as via the sensory nerves that surround blood vessels of the head and neck). The potential candidate vessels include dural arteries, pial arteries and extracranial arteries such as those of the scalp. The role of vasodilatation of the extracranial arteries, in particular, is believed to be significant. Neuromodulators
Adenosine, a neuromodulator, may be involved. Released after the progressive cleavage of adenosine triphosphate (ATP), adenosine acts on adenosine receptors to put the body and brain in a low activity state by dilating blood vessels and slowing the heart rate, such as before and during the early stages of sleep. Adenosine levels have been found to be high during migraine attacks. Caffeines role as an inhibitor of adenosine may explain its effect in reducing migraine.