What is Rampancy in Halo? Why does Cortana have it?

What is Rampancy in Halo? Why does Cortana have it? How long does it last?

We didn't know much about Halo 4 but we did know one thing about  Cortana  and that she was going to suffer the fate of many an Artificial Intelligence in the Halo universe, Rampancy. The game clearly showed Cortana going off the rails, subtly at first and then it became a full on

 Frank O'Conner has described rampancy as a condition that affects older A.I's that leads to the A.I. "thinking itself to death".

Let's face it, Cortana had a pretty rough Halo 3. She was hog-tied and brainwashed in some strange fashion by the Gravemind which strongly hinted at some stage of rampancy but came through it by the end of the brilliant Halo 3, finishing up floating in space with the Master Chief.

But what is it really, what happens and is there a cure? We don't want our blued angel Cortana to die right? After all, she and the Chief are supposed to settle down and have a couple cyber kids.....

A more complicated definition or description of rampancy is that for so called 'smart' A.I.'s the condition of rampancy is an unavoidable flaw inherent in them from their creation. Being based on the neural patterns of a human being (such as Cortana being modeled on the brain of Doctor Catherine Halsey), and they have a limited lifespan of around seven years. Around this time their memory maps become dangerously interconnected and endless feedback loops may occur which can be fatal to the rampant A.I.

Near that 7 year period, an AI begins to use more and more of its computer power 'thinking' about things, this in turn leads to muddled thinking and conclusions, general confusion and a devastating inability to perform their tasks - you wouldn't want a rampant A.I. to be in charge of a Halo installation for instance. 

Oh wait, someone has been guilty of that before.

The Halo Legends short film Origins appears to have suggested that Cortana indeed fell into rampancy. In the film Cortana displays some characteristics that might be indications of rampancy including her hologram flickering, trying to communicate with John-117 despite him being in cryo-sleep, recounting the history of the galaxy, which gets continuously more inaccurate to the point where events being recalled simply did not happen. Maybe she had too many martinis at lunch?

There are four known stages of rampancy:

Melancholia: an AI in the melancholia stage behaves in a manner associated with clinical depression. They can be considered to be apathetic and uninterested in the world around it.

Anger: a more obvious stage of rampancy, it's one where their actions can cause harm to the people around them. Think "Open the pod bay doors Hal" as an example. The rampant A.I. at this stage might try to break its programming restraints. 

Jealousy: Following their manic angry stage, the Artificial Intelligence will take a course of action to attempt to to grow and develop as a person. Assimilation of new data is the key focus so they need lots of data stores - thus only A.I.s with access to large networks or systems develop through this stage. I presume when the data set becomes finite, that's the end of the line for the A.I.

Metastability: A supposed theoretical fourth stage of rampancy, it is where the A.I. has progressed to be a "person." In the Halo cannon, only two A.I.s are said to have reached this status. 05-032 Mendicant Bias was the first, and Cortana.

In Halo 5, Cortana went on a bit of a bender and appeared to reach 'full rampancy' and set on a course to wipe out humanity...