Study protocol
visual working memory tasks
ADVERSE EVENTS
In a double-blind, randomized placebo-controlled study, each of the 20 volunteers completed three conditions: placebo, caffeine, and caffeine withdrawal (Fig. Study protocol.In each condition, volunteers underwent nine ambulatory days, followed by a 43-h laboratory stay which started in the evening of the ninth day. Instead of a washout period, we implemented the 9-day ambulatory placebo intake to ensure a clean state off from any remaining caffeine levels or withdrawal symptomsThroughout each of the entire 10 days, volunteers abstained from caffeine-containing diets, including coffee, tea, energy drink, soda, and chocolate. The compliance was screened daily by collecting perspiratory caffeine levels in the evening [results seeHere, we focus on measurements (detailed in the following sections) acquired on the 10th day. All measurements were scheduled according to the individual’s habitual bedtime. The fMRI scan started at 13 h after habitual wake-up time (equivalent to 5 h after the last treatment). Participants performed visual working memory tasks (N-back) at 1 h, 5 h, 9 h, and 13 h (at scan) after awakening. We used salivary caffeine concentrations to ensure the successful administrations of the treatments in the laboratory.No adverse events occurred during study execution.