Normal Cortical Activity
Neurons across the visual cortex fire in healthy balance.
- -70 mV: Resting Potential (stable neuronal state)
- Normal: Cortical Blood Flow (no perfusion change)
- Regular: Firing Pattern (baseline activity)
- None: Aura Symptoms (no disturbance yet)
Healthy cortical excitability
Neurons hold a stable resting membrane potential.
Ion homeostasis
Sodium-potassium pumps keep gradients tightly balanced.
Vascular tone
Cerebral blood flow stays steady and unremarkable.
Roughly one in three migraine sufferers experience aura before headache.
Depolarization Trigger
A localized wave of depolarization suddenly ignites.
- Occipital: Trigger Zone (visual cortex origin)
- Elevated: Extracellular K+ (sharp surge)
- Spike: Glutamate Release (excitatory surge)
- <1 min: Onset Window (rapid initiation)
Ionic trigger cascade
Extracellular potassium and glutamate rise sharply.
Neuronal-glial coupling
Astrocytes amplify depolarization between neighboring cells.
Threshold crossing
A critical mass of cells depolarizes together.
This trigger point marks the true start of cortical spreading depression.
Spreading Depolarization Wave
The wave crawls outward across cortical tissue slowly.
- 2-6 mm/min: Propagation Speed (typical CSD range)
- Ring: Wavefront Shape (expands outward)
- Growing: Cortical Reach (expands across surface)
- 1944: First Described (by Aristides Leão)
Slow radial expansion
The wavefront advances steadily across cortical tissue.
Cell-to-cell propagation
Depolarization spreads through extracellular ion diffusion.
Leão's discovery
Aristides Leão first recorded this wave in 1944.
CSD speed of 2-6 mm/min matches the slow march of visual aura.
Trailing Neuronal Suppression
Activity falls silent for minutes behind the passing wave.
- 5-15 min: Suppression Duration (per cortical region)
- Silenced: Firing Activity (transient depression)
- Reduced: Blood Flow (oligemia follows wave)
- Gradual: Recovery (activity slowly returns)
Spreading depression proper
Neurons fall silent just behind the wavefront.
Metabolic recovery cost
Restoring ion gradients demands high energy use.
Oligemic aftermath
Blood flow briefly dips behind the passing wave.
This silent zone explains why aura symptoms fade slowly, region by region.
Aura Symptoms & Headache Onset
Visual disturbance unfolds as trigeminal pain pathways ignite.
- 20-30 min: Aura Duration (typical episode length)
- Scintillating scotoma: Visual Symptom (zigzag fortification pattern)
- Triggered: Trigeminal Activation (meningeal nociceptors fire)
- 10-60 min: Headache Delay (after aura begins)
Visual cortex mapping
Cortical position determines the scotoma shape seen.
Trigeminovascular activation
CSD activates trigeminal nerve endings on meninges.
Pain cascade begins
Released neuropeptides trigger meningeal inflammation and pain.
About 90% of migraine pain follows trigeminovascular activation from the wave.