The Killzone is the part of the brain affected by the Flare. This name was adopted after the Flare started infecting people. The disease slowly eats away at the Killzone, turning the infected (known as Cranks) into madmen. WICKED maps the patterns and reactions in the Killzone of those immune to the Flare in order to develop a cure, so they send a number of immune "subjects" into the Trials to obtain these patterns.
The drug known as the Bliss can limit the Killzone's activity. Since the Flare eats away at the brain faster when the brain works harder, the Bliss slows the disease down. If a person, for example, has a lot of stress, the Flare will eat away at the Killzone much faster.