What is a migraine aura?

A migraine aura is caused by something we call cortical spreading depression. It's an electrical wave that spreads over the lining of the brain, the part of the brain that we call the cortex, and it usually manifests itself as a visual disturbance. The kind of symptoms patients will describe are flashing lights, zigzag lines, dark holes in their vision, tunnelling of vision, and, very rarely, even transient loss of vision. It can also manifest itself as a sensory disturbance, by which I mean patients can get numbness or tingling, usually down one side of the body, the arm or the leg. It can also involve the face. The other types of aura are speech aura symptoms where patients will say they have difficulty either comprehending what is being said to them or they understand what is being said to them but they have difficulty speaking. In other words, they have difficulty thinking in terms of what word they want to say, or when they've thought of the word they want to say, they can have difficulty actually saying it. Some will say that they get slurring of speech as well there. So those are the kind of speech aura symptoms you can get. Very rarely, you can get what is called a motor aura where you get weakness on one side of the body, which is obviously very frightening because some people think that they're having a stroke. So those are kind of examples of what we call aura symptoms. They generally last from between five minutes to half an hour, though occasionally they can be longer.