Diminished Nap Effects on Memory Consolidation Are Seen Under Oral Contraceptive Use

Many young females take exogenous hormones as oral contraceptive (OC), a condition rarely controlled for in studies on sleep and memory consolidation even though sex hormones influence consolidation. This study investigated the effects of OCs on sleep-related consolidation of a motor and declarative task, utilizing a daytime nap protocol. Fifteen healthy, young females taking OCs came to the sleep lab for three different conditions: nap with previous learning, wake with previous learning and nap without learning. They underwent each condition twice, once during the 'pill-active' weeks and once during the 'pill-free' week, resulting in 6 visits. In all conditions, participants showed a significant off-line consolidation effect, independent of pill week or nap/wake condition. There were no significant differences in sleep stage duration, spindle activity or spectral EEG frequency bands between naps with or without the learning condition. The present data showed a significant off-line enhancement in memory irrespective of potential beneficial effects of a nap. In comparison to previous studies, this may suggest that the use of OCs may enhance off-line memory consolidation in motor and verbal tasks per se. These results stress the importance to control for the use of OCs in studies focusing on memory performance. (C) 2015 S. Karger AG, Basel