None of the studies we have read measures this. In "Your Brain on ChatGPT", the number of participants in the ChatGPT group with no exact quotation fell from 18 to 4 as early as session 2, even though they were still using ChatGPT. Session 4, in which 9 former users wrote with no tool, gives a result on this point that the document reports in 2 contradictory ways.
Read the source article: AI impact on the brain: what 3 studies show, and their limits