Why is synchrony, rather than just more firing, the signature of a seizure? · Grey Matter

A healthy cortex is busy but loosely coordinated: inhibition keeps each neuron's firing to brief, scattered windows, so neighbours rarely fire in lockstep.

Why is synchrony, rather than just more firing, the signature of a seizure?

A healthy cortex is busy but loosely coordinated: inhibition keeps each neuron's firing to brief, scattered windows, so neighbours rarely fire in lockstep. When inhibition falls behind excitation, a recruited group excites its neighbours faster than they can be held back, and the activity locks into a shared fast rhythm that pulls in more and more tissue. The international definition of a seizure names exactly this (abnormal excessive or synchronous neuronal activity), and synchrony is also what makes a seizure large on the EEG, because aligned currents add up while scattered ones cancel.