All About Auras
Auras are associated with changes in blood flow and nerve activity in the brain. They typically last more than five but less than 60 minutes and signal the approach of the migraine headache. Only about one-fifth of the migraine population experiences aura. Bright visual disturbances that spread across the field of vision are the most frequent type of aura reported. Hippocrates described the “shining light” of visual aura as early as 400 B.C.
Visual Auras
Visual disturbance is often the first sign of migraine in many people, and it is the most common type of aura symptom. It may be gradual, building until the sufferer has trouble focusing on a book or computer screen. Or it may be sudden and hit without warning.
In many migraineurs, visual aura appears in the form of flashing lights (photopsia). It can also cause visual distortion, blurring, and blind spots (scotoma).
A curved, zigzagged band of flashing light that is known clinically as teichopsia or a fortification spectrum because of its resemblance to the design of a fort wall, may be seen in classic migraine. It often sits on the margin of a crescent-shaped blind spot and grows and moves across the visual field as the aura progresses.
These auras can be as brief as five minutes or as long as an hour, but usually peak around 20 minutes after the first visual sign. On average, visual auras last 15 to 20 minutes.
Alert
Visual disturbances that last three to ten minutes, involve a darkening or dimming of vision, and rapidly move across the visual field from the bottom up or from top to bottom, like a shade, may be signs of a transient ischemic attack (TIA), or ministroke, and require immediate medical attention.
Blood flow and magnetic resonance imaging (MRI) have shown that during a visual aura, changes take place in the cerebral cortex — the part of the brain that is responsible for thought, memory, and cognition. Blood flow to this part of the brain is reduced, while the activity of the neurons — the nerve cells that transmit and receive electrical and chemical signals across the brain — are suppressed. That suppression spreads across the cortex at a rate of three to six millimeters a minute, which correlates with the rate at which the aura travels across the visual field. This phenomenon is known clinically as spreading cortical depression.
Nonvisual Characteristics of Auras
Spreading cortical depression can be associated with the mild speech problems (called dysphasia) and one-sided tingling or numbing sensation in an arm or leg (called paresthesia) during an aura. Other nonvisual characteristics of aura include dizziness, weakness, and occasionally, nausea.
