When brain tissue is damaged, whether through infection or trauma, cells that are still capable of some modicum amount of metabolic function will commit slow suicide. This process is called apoptosis.
Apoptosis is a kind of active neuron death in which the neuron, once damaged, shrinks and packages the debris into vesicles where it can be safely removed and redistributed, thus avoiding inflammation and damage to nearby neurons.
Neurons that are too far gone for apoptosis have no choice but to undergo necrosis instead. Necrosis is a passive process in which the damaged cell swells and disintegrates through fragmentation, leading to inflammation that can spread the damage to other healthy neurons in the vicinity. Necrosis happens rapidly whereas apoptosis takes more time.
Most visions of the end of civilization are necrotic ones, outlooks that envision massive destruction, widespread ecological devastation, and immense pain and suffering. But the very tissues of our brains tell us that we have other options.