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 citation needed 

""usually retain their intellectual abilities""
Not even in the handbook for higher education that I used as a reference for some of what I added to this article, not even in that, could I find anything referring to the impairment of intellectual abilities.
From what evidence I can find, there is nothing indicating such an impairment is at all an aspect of ABI, and therfore I am hereby removing the word ""usually"" from the sentence.   "