What decides whether a perturbation in the cortex fades, becomes spreading depression or becomes a seizure? · Grey Matter

Most perturbations fade, because inhibition and ion clearance absorb them.

What decides whether a perturbation in the cortex fades, becomes spreading depression or becomes a seizure?

Most perturbations fade, because inhibition and ion clearance absorb them. In a seizure, neurons keep their gradients and fire too much and too synchronously, since inhibition no longer contains the excitation; in spreading depression the gradients themselves collapse and the tissue goes silent. The two are often described as different distances from a resting state, a seizure closer to normal physiology and spreading depression closer to a full loss of the gradients, and which one occurs depends on local conditions such as extracellular potassium, energy supply and the state of inhibition. They can also follow each other: seizures can trigger spreading depression, which in some models ends the seizure and stops it from spreading.