facto government of Seattle. The series ended with a cliffhanger, with Collier pledging to build the future he had promised, while the government watches uneasily as Collier's militia remains in control of Seattle, now known as Promise City. Promicin In the series, promicin is a fictional neurotransmitter the human body produces that controls and regulates bodily functions. In the 4400, it enables every member to use parts of the cerebellum no human has previously used. This is the cause of the new abilities in each returnee. Promicin's behavior and effects are unpredictable, potentially giving any ability. However, as part of a government conspiracy, every 4400 is regularly injected with a promicin-inhibitor, suppressing their potential new abilities. Since the government ceases injecting promicin inhibitor, every 4400 develops an ability. Dr. Kevin Burkhoff devises a way to artificially create 4400 abilities through a series of promicin injections, using himself as a test subject, giving him regenerative abilities. However, the government finds out about this breakthrough and builds up its own stockpile of a much purer promicin (extracted from Isabelle Tyler), which they in turn use to create at least one group of soldiers with 4400 abilities, as demonstrated by the government's attack on Promise City. Jordan Collier steals the government's supply, and begins distributing it via human couriers to anyone who wants the shot. An injection of promicin has a 50% chance of either killing the person taking the injection (by way of an aneurysm) or giving them a 4400 ability. In the fourth season, Dr. Burkhoff claims to have discovered how promicin interacts with the body, thus being able to predict whether a person will survive the shot or not. It is explained that nine out of ten left-handed people who take the shot survive. In the brain there is a small part called the corpus callosum. It is essentially a bundle of neural fibres that connects the two hemispheres and it is usually slightly larger in left-handed people than it is in right-handed people. That is why left-handed people survive; the size of that part of the brain helps determine whether or not a person will be able to integrate a new neurotransmitter. With further research, Dr. Burkhoff believes a simple CAT scan will be able to tell how anyone's body will react to a promicin shot. There exists a substance that can eliminate all traces of promicin in the