Scientific Study Randomized Controlled Trial: Regular Caffeine intake impairs working memory & prolongs reaction time in young, healthy non-smokers  (self.Nootropics)
Brain activity during a working memory task after daily caffeine intake and caffeine withdrawal: a randomized double-blind placebo-controlled trial
In this study, 20 healthy non-smoker volunteers were recruited. Their average caffeine intake before the study was 474mg / day, therefore, a dose of 450mg / day (split into 3 doses of 150mg) was decided for the caffeine group in this study. The caffeine group received 150mg 3 times a day for 10 days. There were also 2 other groups: the withdrawal group and placebo group. The withdrawal group received 150mg 3 times a day for 9 days, then 1 day of placebo - and the placebo group received a placebo 3 times a day for 10 days (making them go through 10 days of withdrawal from their pre-study caffeine intake).
In a working memory (WM) task (N-Back), it was found the caffeine group had significantly worse performance than placebo, with the withdrawal group having similarly bad performance. The caffeine group also had a longer reaction time than the placebo group. It's worth reminding the placebo group was 10 days off caffeine, while the withdrawal group was just 1 day off caffeine - so the negative effects of caffeine on working memory seem to normalize 10 days, but not 1 day, after cessation of daily intake.