the lever-rat: pressing until it dies — "even if the pleasure-electrode was removed…"

The book's core emblem of addiction rendered in laboratory form — addiction with the substance stripped away, reduced to pure circuitry. The rat pressing its pleasure-lever "thousands of times an hour... ignoring food and female rats in heat" until it dies of dehydration is the substance-cage at its most literal: reward decoupled from survival, pleasure that outcompetes every other drive including staying alive. And the detail that removing the electrode doesn't stop the behavior — the animal still "run around pressing anything that could be pressed" — is the theme's whole thesis about the Disease outliving the drug: the compulsion is in the wiring, not the chemical, and persists after its object is gone.