There is no one experience of “aura.” For some, it starts with white glitter at the edge of their vision like half-seen falling stars; others find faces distorted or words suddenly difficult to form. Science journals collect unusual cases, like Oliver Sacks’ account of waking to find his nurse had “become inorganic” and was drifting apart like a set of mosaic tiles. In rare cases, an individual can feel they are suddenly growing to an enormous size or shrinking entirely out of view—known as Alice in Wonderland Syndrome.
For most, these auras appear as if from nowhere, most commonly as a set of scintillating zigzags that grow for about 20 minutes across the edge of the field of vision. Intriguing in themselves, these phenomena are dire omens. They forewarn of the arrival, in less than an hour, of the sustained pain of a migraine.
Migraines are the world’s third most prevalent cause of disability, affecting a billion people each year by some estimates. About a third experience some form of aura beforehand, often accompanied by debilitating symptoms from vomiting to vertigo, or, in worse cases, temporary blindness or hemiplegia, a paralysis down one side of the body. But recent discoveries about mechanisms that link auras and migraines could lead to potential new treatments. Martin Kaag Rasmussen, a neuroscientist at the University of Copenhagen, says research on auras may reveal new answers to the greatest riddle of migraines: How do painful headaches arise from the brain if it has no pain receptors?
The brain, like other internal organs, is insensate, its lack of sensory receptors attested by videos of virtuoso violinists who play on unfazed as neurosurgeons go to work inside their skulls. The central nervous system, the brain and the spinal cord, is usually considered sealed off behind the so-called blood–brain barrier, explains Rasmussen. But auras—which fMRI scans have indicated originate as a sort of rolling blackout within the brain—suggest information is getting through from the brain to the pain sensors in the peripheral nervous system, the nerves outside of the central nervous system that extend across the rest of the body. “But how and where does it communicate?” asks Rasmussen. “Migraine with aura is sort of the perfect model to use to answer this question.”
Rasmussen is a coauthor of a study in mice published in July that found a tiny opening between the cerebrospinal fluid, a clear soup of nutrients that bathes the brain and spinal cord, and pain receptors in the jaw—a previously undetected point of contact where substances released in response to brain activity could activate the peripheral nervous system. This discovery sets a new direction for migraine research that could help identify new drug targets. Some neurologists think it could change how we think about headaches.
Nouchine Hadjikhani, a Harvard neuroscientist who has been researching auras for three decades, says the research is “probably the biggest advance” in 10 to 20 years about how migraines happen. Around the turn of the millennium, we learned that auras occur during a temporary shutdown of neuron activity, known as a cortical spreading depression (CSD). Hadjikhani’s team was the first to show this in humans on fMRI scans, as a slow-moving wave of cells activating anomalously, rippling across the cerebral cortex. “Imagine you throw a stone in water and you see the waves going out,” she says. Most aura symptoms are visual because more than a third of the brain is dedicated to visual processing.
