Migraines are a complex neurological condition involving more than just a severe headache. Many individuals report temporary visual disturbances, which are sometimes confusingly categorized as hallucinations. These visual events are a recognized symptom of a migraine attack, typically preceding or accompanying the onset of head pain.
Migraine Visual Phenomena: Aura vs. Hallucination
The visual changes experienced during a migraine are most often a phenomenon called an aura, which is a neurological event that differs significantly from a true hallucination. A migraine aura is characterized by “positive” visual symptoms, meaning the appearance of something that is not actually there, followed by “negative” symptoms, which are areas of vision loss. These events usually affect both eyes and are temporary, resolving within five to sixty minutes.
The most common visual aura is the scintillating scotoma, which typically begins as a small, shimmering or sparkling area near the center of vision. This area then slowly expands, often taking on a classic zigzag pattern with brightly colored or black-and-white edges, sometimes referred to as a fortification spectrum. As the scintillating edge expands outward, it leaves behind a blind spot, or scotoma, in its wake, before the visual field returns to normal.
True visual hallucinations, in contrast to auras, are much rarer in the context of a typical migraine. Hallucinations involve seeing fully formed objects, such as animals, people, or complex scenes that do not exist. These complex, formed hallucinations are usually associated only with specific, uncommon migraine variants, such as familial hemiplegic migraine. The vast majority of people experiencing visual phenomena during a migraine are experiencing an aura, which is a disturbance of vision.
The Neurological Basis of Migraine Visual Disturbances
The underlying biological process that causes the visual disturbances of a migraine aura is known as Cortical Spreading Depression, or CSD. CSD is characterized as a slow-moving wave of intense neuroelectric activity that sweeps across the brain’s outer layer, the cortex. This wave involves a depolarization of both neurons and glial cells, which is essentially a massive, temporary change in their electrical charge.
The visual aura manifests because this wave of CSD most commonly begins and propagates through the occipital lobe, the region of the brain dedicated to processing visual information. The initial phase of the CSD wave causes a brief period of neuronal hyperactivity, which generates the “positive” symptoms, such as the flashing lights and zigzag patterns seen in the aura. This hyperactivity then gives way to a prolonged period of suppressed neural activity, or depression, as the wave passes.
This wave of suppressed activity causes the “negative” symptoms, resulting in the temporary blind spot that follows the scintillating edge. The CSD wave travels across the cortex at a uniquely slow rate, typically between 2 to 5 millimeters per minute. This slow speed of propagation directly correlates with the gradual expansion and movement of the visual aura that patients perceive.
When Visual Changes Signal Something Else
While most migraine-related visual changes are benign auras, certain characteristics require immediate medical attention as they may indicate a more serious condition. A key distinction is whether the visual change is a loss of vision in only one eye, which suggests an eye or vascular issue, not a typical migraine aura. Migraine auras, being a brain event, affect the visual field of both eyes simultaneously.
Visual symptoms that last significantly longer than the typical 60-minute window for an aura should also be evaluated promptly. Additionally, any sudden, complete loss of vision in one eye, known as amaurosis fugax, suggests a potential problem with blood flow to the eye or brain, such as a transient ischemic attack (TIA) or a stroke.
Visual changes accompanied by new neurological symptoms, such as sudden weakness, difficulty speaking, or severe balance problems, are concerning. When any visual disturbance occurs for the first time, especially if it is sudden, painful, or completely unlike previous auras, consultation with a healthcare provider is necessary to rule out other potential causes.