The EEG‐indexed impacts of caffeine on auditory novelty processing across phases of the human menstrual cycle

Caffeine, the most used global stimulant, can impact neurocognition. Hormonal fluctuations occurring across the human menstrual cycle affect similar cognitive domains. Research is needed to identify whether the purported cognitive-enhancing effects of caffeine vary across menstrual cycle phase. The objective of this study was to examine the impact of caffeine on EEG-derived markers of auditory change detection and novelty processing (MMN, P3a, P3b and RON) across phases of the menstrual cycle in naturally cycling females. Participants were randomly assigned to complete the experiment while in their menstrual (n = 31), follicular (n = 26) or luteal (n = 29) phase, completing two sessions wherein they were administered either a caffeine pill (200 mg, oral) or a placebo in a counterbalanced order using a randomized, double-blinded procedure. Auditory tone detection was assessed via a novelty oddball task while EEG data were collected. Caffeine significantly enhanced target detection at both the neural (P3b, MMN and RON) and behavioural levels, with effects most prominent in the menstrual phase. Additionally, P3a and P3b amplitudes differed significantly between phase groups under placebo conditions but not under caffeine conditions. Caffeine significantly enhanced target detection at both the electrophysiological and behavioural levels, with these effects mostly limited to the menstrual phase. Additionally, there were significant differences in ERP activity between all menstrual phases under both placebo and caffeine conditions. Our results suggest that caffeine enhances auditory novelty processing, particularly during the menstrual phase, though future research is needed to further explore the intersection of caffeine and the HMC.