Anecdotal evidence that aspartame disrupts memory has been growing since the sugar substitute was approved in the early 1980s, though attempts to prove the claim have so far been equivocal. Previous studies have tested memory by asking aspartame users to remember lists of words or numbers -- tests of short-term memory. But according to Timothy M. Barth, Ph.D., a psychology professor at Texas Christian University, those studies focused on the wrong type of memory.
In his study of 90 students, Barth found that participants who regularly drank diet sodas containing aspartame performed as well as nonusers on laboratory tests. However, aspartame users were more likely to report long-term memory lapses like forgetting details of personal routines or whether or not a task had been completed.