In Fear of Breakdown (1974), Winnicott considered the health and pathological aspects as related to the integration-disintegration dynamics, that depend on the facilitating environment:
The individual inherits a maturational
process. This carries the individual along in so far as there exists a facilitating environment, andonly in so far as this exists. The facilitating environment is itself a complex phenomenon and needs special study in its own right; the essential feature is that it has a kind of growth of its own, being adapted to the changing needs of the growing individual. The individual proceeds from absolute dependence to relative independence and towards independence. In health the development takes place at a pace that does not outstrip the development of complexity in the mental mechanisms, this being linked to neurophysiological development. The facilitating environment can be described as holding, developing into handling, to which is added object-presenting. In such a facilitating environment the individual undergoes development which can be classified as integrating, to which is added indwelling (or psychosomatic collusion) and then object-relating. This is a gross over-simplification but it must suffice in this context. It will be observed that in such a description forward movement in development corresponds closely with the threat of retrograde movement (and defences against this threat) in schizophrenic illness.
He use the term „integration” in several (but complementary) ways. In „Ego integration in child development” (1962) even recognize:
The main trend in the maturational process can be condensed into the different meanings of the word „integration”
and until the end of the article only talks about these meanings (it would be nice to be back with a comment to summarize them).
I think that is possible as „unintegration” to have several meanings, as you well have quoted from the „Capacity to be alone”, but I do not think that this term substitutes „disintegration”; In From pediatrics to psychoanalysis, in the quote that you gave to be more precise, I am not sure that „unintegration” has the same meaning as „disintegration”, or perhaps Winnicott refers to mental unintegration areas (islands) that exist in psychosis, that is also an idea of Andre Green.
That remembers me another question, addressed by one of the Cafe Gradiva readers, concerning the „emergence” of psychosis at a certain age to which an individual has functioned normally. Here’s the answer in Winnicott’s words, and I give a broader quote:
Splitting occurs in a person and organize because of the environment failure. There was for everybody an expected failure of the environment. As I often say, a baby is usually cared by a good enough mother. Well, being a good enough mother failed (maybe she was sick), or she has not been good enough. I will not make accusations, but just looking etiology. These issues are more easily applicable in childhood or early childhood schizophrenia, but we must find a way to apply them on adult and adolescent schizophrenia, even when it seems that things are going well in early childhood and disorder is manifested clinically only later. The fact is that early addiction continues to have meaning, especially in adolescence and, perhaps, in a disguised form, the whole life.