Part 5: The Electrical Storm Behind Migraine Aura
Imagine dropping a pebble into the middle of a calm lake.
The pebble creates a ripple that slowly expands outward in every direction.
Now imagine something similar happening—not in water—but across the surface of the brain.
This is one of the leading theories behind migraine aura.
Researchers call it cortical spreading depression (CSD), and despite its somewhat gloomy name, it has nothing to do with depression in the emotional sense. Instead, it describes a slow-moving wave of electrical activity that travels across the outer layer of the brain, temporarily changing how neurons communicate.
It is one of the most remarkable discoveries in migraine science.
An Electrical Wave Across the Brain
Unlike a seizure, where millions of neurons fire rapidly and continuously, cortical spreading depression is more like a traveling wave.
A brief burst of intense neuronal activity is followed by a temporary period in which those same neurons become much quieter than normal.
This wave moves remarkably slowly—only a few millimeters each minute—as it spreads across the cerebral cortex.
As it passes through different regions of the brain, it temporarily alters their normal function.
And that's where things become clinically interesting.
Why Aura Changes Over Time
Patients often describe their aura as something that gradually grows or moves.
Perhaps a small shimmering spot slowly expands across their vision.
Or tingling begins in the fingertips before gradually spreading into the hand and face.
That gradual progression is one of the clues that migraine aura originates in the brain itself.
As the wave of cortical spreading depression moves through different functional areas of the cortex, patients experience symptoms that reflect the job of that particular brain region.
If the wave travels through the visual cortex, visual symptoms occur.
If it affects sensory cortex, numbness or tingling may develop.
If language areas become involved, temporary word-finding difficulties can appear.
The symptoms aren't random.
They're a map of where the brain is temporarily changing its activity.
More Than Just Aura
One of the reasons researchers became so interested in cortical spreading depression is that it may explain much more than aura alone.
Evidence suggests this electrical wave may also activate deeper brain structures involved in migraine pain, including the trigeminovascular system.
In other words, cortical spreading depression may represent one of the earliest events in a much larger migraine cascade.
Exactly how that transition occurs remains an active area of research, but it reinforces an important concept we've discussed throughout this series:
The headache doesn't appear out of nowhere.
It develops as part of a changing neurologic state.
The Great Paradox: If Brain Activity Decreases, Why Does the Headache Get Worse?
At first glance, cortical spreading depression seems backwards.
After the initial wave of electrical activity, the affected neurons actually become less active, not more.
So why would decreased brain activity lead to more pain?
The answer lies in what happens next.
As cortical spreading depression moves across the cortex, blood flow briefly decreases in the affected region—a phenomenon called hypoperfusion. Fortunately, this reduction in blood flow is temporary and does not represent the dangerous loss of circulation seen in stroke.
Instead, the brain quickly responds.
Blood flow rebounds above normal in a process called reactive hyperemia. This surge helps deliver oxygen and nutrients, clear metabolic byproducts, and restore normal neuronal function.
For many years, researchers believed these blood flow changes were the cause of migraine.
Today, they're viewed differently.
Rather than causing migraine, these vascular changes appear to be the brain's response to changing neuronal activity.
Importantly, this reactive increase in blood flow also appears capable of setting off inflammatory signaling that contributes to the headache phase of migraine.
In other words, the headache may not result directly from cortical spreading depression itself, but from the cascade of events that follows.
Why This Matters for Acupuncturists
You don't need to memorize the molecular details of cortical spreading depression to become a better clinician.
But understanding that migraine begins as a dynamic change in brain activity helps explain why patients experience symptoms before the headache, why aura evolves over time, and why migraine is so much more than a vascular disorder.
It also reinforces one of the central themes of modern migraine science:
Migraine is fundamentally a disorder of altered brain function and sensory processing.
Key Takeaways
Cortical spreading depression is believed to underlie most migraine aura.
It consists of a slow-moving wave of altered electrical activity traveling across the cerebral cortex.
The symptoms of aura often reflect which part of the brain the wave is passing through.
CSD may help initiate the broader cascade of events that ultimately produces migraine pain.
Understanding CSD shifts our perspective from migraine as a headache disorder to migraine as a disorder of dynamic brain activity.
Suggested Reading
- Dodick, D. W. (2018). A Phase-by-Phase Review of Migraine Pathophysiology. Headache, 58 Suppl 1, 4-16. doi:10.1111/head.13300
- Goadsby PJ, Holland PR, Martins-Oliveira M, Hoffmann J, Schankin C, Akerman S. Pathophysiology of Migraine: A Disorder of Sensory Processing. Physiological Reviews. 2017.
Continue Rethinking Migraine
This is Part 5 of the Rethinking Migraine series.
Previous Article → Part 4: Migraine Aura—More Than Just Visual Disturbances
Next Article → Part 6: Why Pain Doesn't Begin Where You Think It Does
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