Those of you who do not want to know about Van der Hart's et al's 2006 research should avoid this thread please! Do not read further and then complain please! Also, I am not a therapist. This is a discussion of public material found in books, etc..
First of all

No one has a truly single, or unified, personality.

All humans have ego states, so its confusing when this term is used for DID/DDNOS.
An ego state is simply those different parts that do different tasks in one person: The Mom, The driven employee, the carefree dancer, etc.... An Ego States IS NOT a Dissociative part! ...even though the acts it performs may be unconscious.
So what is a personality?

All People are made up of "many diverse, fragmentary—and generally illusory—images of “self.” Psychologists named these normal parts "Ego states."
An Ego State is NOT unique to DID/DDNOS. It is unique to all HUMANS! At least I don't think other animals have it, it they do they are the higher evolved ones.

------------------------------------------------------
DID/DDNOS Brain
This is an abnormal brain. Those ego states have become compartmentalized so that communication between them is difficult. In DID we often call these parts Alters because they are so compartmentalized they have taken on characteristics and have been divided from communication with the other parts of themselves so they continue to become more unique into themselves. (just as you would if you were not around a group of friends or family. You would become isolated and unique. When around others, they influence who you are by communication)
------------------------------------------------------------------------------
This information is summarized on this subject from E. Howells wonderful book!

Understanding and Treating DID - A Relational Approach
By E. Howell
Note: Self State is often used for either Ego or Alter
page 7-8 intro
"Non-DDNOS/DID People

WE all have multiple self states. For all of us, our mental life is characterized by constant changes in self-state to match the current context. Much of the time, most of us are aware (although less often than we think) of the matches of self-state to context, and we remember both (or we think we do). For example, we may wear a therapists hat while in the office, have a care-giving orientation when in contact with our children and respond in a different way involving early attachment system internal working models, when speaking to our parents.




****What is important for psychological health is the degree of dissociation between self-states or, to put it more positively, the degree to which we experience our multiple self-states as contextually interrelated and part of what comprises the sum of who we are.
...the idea of unitary, continuous 'self' is actually an illusion our minds attempt to create... We have multiple and varied 'selves,' which are needed to carry out the many and diverse activities of our lives." (Siegel pg 231)
So that is pretty much saying what I said in the first part of the post.

-------------------------------------------------------------------------------
Contextualization - Making of DDNOS/DID












In infancy, behavior is organized as a set of discrete behavioral states, such as states of sleep and waking, eating,elimination, and so on. these behavior states become linked over time and grouped together in sequences. Psychological trauma impedes this linkage: as a result, individuals who have been severely neglected or highly traumatized in childhood have not had the interpersonal attention, support and encouragement necessary to interconnect their self-states and the varying contexts of their lives.
This paragraph above is very important to understand.



Early childhood trauma by a trusted caretaker results in at least:
Change of Brain Structure
Increases Stress Hormones
Affects the Endocrine System
Numbs the sociation of certain areas of experience from consciousness

Questions?