Scientific American has an article on migraines that takes a comprehensive look at the science of this painful and hallucinatory disorder.
The piece updates the science on migraines from the traditional but oversimplified ‘constricted blood vessels’ explanation to explore the interplay between nerves, neurotransmitters and lifestyle.
A crucial process seems to be cortical spreading depression that may be responsible, at least in part, for both the intense pain and the aura:
Aura appears to stem from cortical spreading depression‚Äîa kind of ‚Äúbrainstorm‚Äù anticipated as the cause of migraine in the writings of 19th-century physician Edward Lieving. Although biologist Aristides Le√£o first reported the phenomenon in animals in 1944, it was experimentally linked to migraine only recently. In more technical terms, cortical spreading depression is a wave of intense nerve cell activity that spreads through an unusually large swath of the cortex (the furrowed, outer layer of the brain), especially the areas that control vision. This hyperexcitable phase is followed by a wave of widespread, and relatively prolonged, neuronal inhibition. During this inhibitory phase, the neurons are in a state of ‚Äúsuspended animation,‚Äù during which they cannot be excited.
Neuronal activity is controlled by a carefully synchronized flow of sodium, potassium and calcium ions across the nerve cell membrane through channels and pumps. The pumps keep resting cells high in potassium and low in sodium and calcium. A neuron ‚Äúfires,‚Äù releasing neurotransmitters, when the inward flow of sodium and calcium through opened channels depolarizes the membrane‚Äîthat is, when the inside of the cell becomes positively charged relative to the outside. Normally, cells then briefly hyperpolarize: they become strongly negative on the inside relative to the outside by allowing potassium ions to rush out. Hyperpolarization closes the sodium and calcium channels and returns the neurons to their resting state soon after firing. But neurons can remain excessively hyperpolarized, or inhibited, for a long time following intense stimulations.