From the 100's of pages of literature ive read, mdma has been shown to cause some cognitive defects in HEAVY polydrug users, so? Not entirely unexpected hey! And they are fine 1 year after use has stopped.

Show any data on light recreational use i.e. using upto 200mgs upto 4 times per year. You will not find anything because at that dose/frequency, it is not damaging.

That is what i'd suggest anyone new to the drug to do, and no more.