How does aspartame affect our bodies?

I have read about aspartame's daunting history, and it indeed has one. Since its discovery in the 1960's, aspartame has had years of experimentation. The data received has shown that a considerable amount of animals died from being injected with aspartame: with holes developing in the animals brain.

How exactly is our brain affected by aspartame?
and does aspartame lead to any symptoms?

Any information on aspartame would be helpful!