I am researching emotive portraits for an art project I am working on.
I haven't been able to find a lot of information. The major emotions
are: happiness, surprise, anger, sadness, fear, and frustration. I
would like to know how these emotions developed in history through
different artists. what techniques did the use to make those emotions
appear stronger and more realistic? I would also like to know how
these different emotions are portrayed in different cultures: if they
are understood differently in different places. I know this is a
pretty complex question, so an answer to any or all parts of the
question would be great. thank you.

Colors - blue mood  , red with anger

Exaggeration - as in "The Scream"

Look at your own face in a mirror.

So many of the old masters are dark and muddled from age.  Cleaning
wold reveal a different emotion.

How you happen to be feeling the day you visit the gallery.

You have a lot to explore. Good Luck.

You've certainly bitten off a lot - hopefully not too much - to chew.
One artist you might wish to focus on is Rembrandt, who is generally
recognised as a master at expressing human emotions in both his
paintings and etchings. In some of his earlier etchings he used
himself as a model, looking at his own face in a mirror, as he changed
his facial expressions. There's quite a lot of material on the web
about Rembrandt's handling of human emotions, including the following
3 websites:

http://thomonthenet.com/?p=EtchingRembrandt&t=s

http://www.world-science.net/exclusives/051013_rembrandtfrm.htm

http://collegerelations.vassar.edu/2006/2103/

Yes indeed, a very broad subject.  
This site may be of interest:
http://www.sruweb.com/~walsh/intro_unit_five.html

I found it, looking for the source of the four emoting busts pictured.
 They are part of a collection in a museum, I believe, in France. 
Couldn't find it.
But one artist's representation is only a snapshot, and you want the whole movie.

This could also be interesting:
http://www.sruweb.com/~walsh/intro_unit_five.html
http://www.worldwideschool.org/library/books/sci/lifesciences/TheExpressionofEmotioninManandAnimals/Chap0.html

One type of source for representations of different emotions in
Western art is religious works relating to Christ's Passion: carvings,
paintings and frescos showing several/many persons with differing
emotional responses.  Also pictures of The Last Judgement include
persons showing varied emotions: the damned and the saved.  Sites such
as these discuss:
http://www.artcyclopedia.com/featuredarticle-2001-04.html
http://www.lifeinitaly.com/art/early-renaissance-2.asp
http://en.wikipedia.org/wiki/Gothic_art
http://www.hnanews.org/2005/fellowships.html

Rodin's "The Burghers of Calais" is another snapshot.

Just a bit of a start.  Good luck!