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An aura is a phase of migraine driven by a wave of electrical activity called cortical spreading depression (CSD) that moves across the surface of the brain at approximately 1 millimeter per minute, meaning it travels across the whole brain in about 30 minutes.
As the wave moves, it touches each neuron in sequence. The occipital lobe, the brain's visual processing center, recognizes this electrical activity but cannot tell whether it is coming from the eyes or from within the brain itself. The result is what you see during an aura: flashes, spots, shimmer, or patterns that correspond to neurons firing as the wave passes through them.
The dark or blind spots that sometimes appear alongside or instead of visual patterns tell the opposite story, they correspond to regions where neurons have gone quiet, their ion channels closed and unable to pass electrical signals. This ionic imbalance is the neurological event itself. For many migraineurs it is followed by the headache phase, but not always, some people experience aura as their primary or only symptom, with no pain following. Whether or not a headache develops, the underlying disorder is migraine, and the aura is one of its symptoms.
Approximately 25-30% of people with migraine experience aura, and of those, around 90% experience the visual type. Most have had it for years before recognizing what it is.
Read Are You Experiencing an Aura? for the foundational explanation.
This blog covers the five most searched aura patterns, what they look like, what they mean, and what to do when they appear.
What it looks like: A blind spot, called a scotoma, typically starts as a small area of missing or blurred vision, often near the center of the visual field. It may appear like a dark patch, a grey smear, or simply a hole in what you can see. The edges of the blind spot are often where the visual activity concentrates, which is why scotomas frequently appear with a shimmering or flickering border rather than a clean edge.
What is happening: The cortical spreading depression wave is moving through the visual cortex, the region at the back of the brain that processes everything you see. As the wave suppresses electrical activity in a region of the visual cortex, the corresponding area of your visual field goes dark or blurry. The brain does not simply see nothing in that spot, it often fills it in with whatever it expects to be there, which is why blind spots can be easy to miss until they are large enough to disrupt reading or driving.
What to watch for: A scotoma that appears suddenly, does not move gradually over 5-20 minutes, lasts more than an hour, or appears in only one eye (rather than affecting the same region in both eyes) warrants medical attention, it can be a sign of something other than migraine aura.
What it looks like: Zigzag or angular shimmering lines, often described as a crescent, a C-shape, or a fortification pattern (like the aerial view of a fortress wall), that typically begin near the center of vision and expand outward toward the periphery over 10–30 minutes. They shimmer, flash, or pulse, and are often described as resembling heat waves, a kaleidoscope, or broken glass catching light. This is called a scintillating scotoma and is the most classic and recognizable aura pattern.
What is happening: As the cortical spreading depression wave moves outward from its origin point, it activates neurons in the visual cortex in sequence. The shimmering zigzag border represents the active edge of the wave, the neurons in the process of firing and then going quiet. The expanding crescent shape reflects the map of visual space in the cortex: neurons that process central vision are in the middle, peripheral vision neurons are toward the edges, so the pattern expands outward as the wave travels.
What to watch for: The scintillating scotoma typically lasts 20-30 minutes and then fades as the wave completes its journey across the visual cortex. It is one of the most reliably benign aura patterns, but if zigzag lines appear with sudden severe headache, weakness on one side of the body, or speech difficulty, seek emergency medical care.
What it looks like: A narrowing of the peripheral visual field, as if the edges of what you can see are closing in, leaving only central vision intact. Some people describe it as looking through a tube or a narrowing window. Others experience it as a graying or darkening at the outer edges of vision rather than a complete loss.
What is happening: Tunnel vision as an aura symptom reflects cortical spreading depression affecting the neurons that process peripheral vision, which are located toward the outer edges of the visual cortex. When the ionic shift of CSD reaches those neurons, their channels close and the corresponding region of the visual field goes dark or narrows. It can also occur in brainstem aura, where the CSD-driven ionic disruption affects regions of the brainstem involved in visual and sensory processing, producing a broader set of symptoms including tunnel vision alongside dizziness, difficulty speaking, or tingling on both sides of the body.
What to watch for: Tunnel vision that comes on suddenly without the gradual build of typical aura, lasts longer than an hour, or is accompanied by other neurological symptoms should be evaluated promptly to rule out causes other than migraine aura.
The clinical definition of aura includes symptoms that develop gradually over at least 5 minutes and typically last between 5 and 60 minutes. Most visual auras resolve within 20-30 minutes. The International Headache Society's diagnostic criteria specify that aura symptoms should not persist beyond one hour, aura lasting longer than 60 minutes is classified as prolonged aura and warrants investigation.¹
Headache typically follows within 60 minutes of aura onset, though it can begin during the aura or, in some cases, not come at all.
What it is: Aura that occurs without the headache phase is called acephalgic migraine, silent migraine, or migraine equivalent. It is more common than most people realize and is frequently misdiagnosed as a visual disturbance, anxiety, or, particularly in older adults experiencing it for the first time, a transient ischemic attack.
Why it happens: Cortical spreading depression is not simply a precursor to migraine pain, it is the brain's own mechanism for resolving an electrolyte imbalance. The ionic shift of CSD redistributes sodium, potassium, calcium, and other ions across the brain in a large-scale depolarization wave specifically generated to correct the electrolyte disruption that is causing instability. When CSD successfully restores sufficient electrolyte balance, the pain phase never develops. When it does not fully resolve the imbalance, the headache follows. Aura without headache is not a different condition, it is the same channelopathy expressing itself in a brain that was able to correct the ionic disruption on its own, or in one that received enough electrolyte support in time to allow CSD to complete its work without tipping into the pain phase.
This is also why acting on aura immediately, taking salt and water at the first sign of visual disturbance, can sometimes prevent the headache phase entirely. The intervention supports the ionic environment CSD is attempting to restore, giving the brain a better chance of completing that resolution before pain signaling begins.
What to watch for: Sudden onset without gradual build, symptoms lasting longer than an hour, or accompanying weakness or speech difficulty warrant prompt medical evaluation to rule out causes other than migraine.
Every aura pattern described above represents the same underlying event: a wave of electrical activity moving across the brain, depleting ions as it goes. Sodium, potassium, calcium, and magnesium all shift dramatically during cortical spreading depression. By the time aura is visible, the ionic disruption is already underway.
This is also why acting on aura immediately, taking salt and water at the first sign of visual disturbance, can sometimes prevent the headache phase entirely. The intervention supports the ionic environment CSD is attempting to restore, giving the brain a better chance of completing that resolution before pain signaling begins. Health By Principle's Complete Electrolytes support consistent sodium balance throughout the day,so the extracellular environment the migraine brain depends on is already maintained before aura appears, not just in response to it.
Visual disturbances are the most recognized aura patterns, but they are far from the only ones. Research into migraine physiology documents 34 distinct aura signals that migraineurs may experience, many of which are never recognized as aura at all. These include:
Many migraineurs have been experiencing aura for years, in these subtler forms, without ever connecting it to migraine. If any of these patterns feel familiar, they are worth tracking. Recognizing an aura in its earliest form is the most valuable window you have to intervene before the headache phase begins.
Related Reading on Health By Principle
Sources
1. Stanton AA - Fighting the Migraine Epidemic: A Complete Guide: How to Treat and Prevent Migraines Without Medicines. 2nd ed. Angela Stanton Publishing, 2020. (Primary protocol reference - full documentation of aura signals and migraine physiology)
2. International Headache Society - ICHD-3: Migraine with Aura. ichd-3.org
3. Petrusic I, Zidverc-Trajkovic J - Migraine Aura: Features, Pathophysiology, Assessment and Perspectives for Future Treatments. Expert Review of Neurotherapeutics, 2019. PMC6134860
4. Goadsby PJ, Holland PR, Martins-Oliveira M, et al. - Pathophysiology of Migraine: A Disorder of Sensory Processing. Physiological Reviews, 2017;97(2):553–622. DOI: 10.1152/physrev.00034.2015
5. American Migraine Foundation - Visual Disturbances: Related to Migraine or Not? americanmigrainefoundation.org
6. Healthline - Types of Migraine Aura. (Secondary source) healthline.com
