Alicia,
    When formula was home-made, the cows milk was diluted with water to reduce
the protein and salt content,  which made the carbohydrate and fat content too
low.  So corn syrup or sugar for carbo and vegetable oil for lipids were
added.  I beleive this is still the process, I do not know if the milk is
skimmed first to remove the bovine fats by commercial manufacturers.
        As for brain growth, the issue is linolenic acid, arachidonic acid and
DHA.  There was concern a few years ago about powdered formula having too much
linoleic acid, which actually inhibits formation of linolenic.  Seems the
manufacturers were unable to preserve soy oil in powdered formula, the better
source of linoleic acid; so used corn or other oils high in linoleic. I am
pretty sure this issue was addressed by finding a better preservative and
switching to soybean oil.  This of course is only a tiny piece of the brain
development puzzle.
Catherine Watson Genna, IBCLC