This is not a subject I know much about, but a few years ago I did a small
project on the effects of aspartame on learning and I came across a few
references you might find useful:
Ferguson, J.M. (1985) Interaction of aspartame and carbohydrates in an
eating-disordered patient. Am. J. Psychiatry 142:271.
Walton, R.G. (1986) Seizure and mania after high intake of aspartame.
Wurtman, R.J. (1983) Biochemical changes following high-dose aspartame with
dietary carbohydrates. New England J. Med. 309:429-430.
Sorry these are all older papers. I seem to recall that Wurtman was doing
a lot of work on aspartame and there may be some more recent publications.