Motor memory consolidation potentiated by exposition to a conditioned stimulus in stage 2 sleep

Abstract

Introduction Motor sequence learning refers to the process by which simple, stereotyped movement elements come to be performed effortlessly as a unitary sequence through multiple sessions of practice. Numerous studies have convincingly demonstrated that sleep (at night and daytime) plays a critical role in the consolidation of motor sequence learning. Yet there is no consensus regarding the sleep stages implicated in the consolidation of various motor skills. Mounting evidence indicates that stage 2 sleep and spindle activity in particular, are critical for motor memory consolidation to occur, but most of those studies are only correlational in nature. In this study, we probed a possible causal role of stage 2 sleep in motor memory consolidation using an olfactory stimulation/motor sequence learning (MSL) conditioning protocol. Materials and methods We conditioned a first group of participants ( n = 26) with a rose-like odor during learning of a sequence of finger movements, and re-exposed them to the odor during stage 2 sleep (ST2). A second group ( n = 26) was conditioned with the same odor while doing the MSL task and was re-exposed during REM sleep (REM). Finally, a third group ( n = 22) was not conditioned with the odor during the MSL task, but was exposed to it during stage 2 sleep (CTL). All subjects were re-tested in the morning 2 h after waking up. Performance was assessed by comparing the mean time to complete the four first blocs of retest to the four last blocs of training. Results Analysis of gains in performance revealed a significant interaction between the experimental manipulation and participant’s gender ((F(2,68) = 5.10, p = .01). Gains were significantly higher for men than women in the ST2 group ( p = .01). Also, results demonstrated that men in the ST2 group showed greater gains in performance than those in the CTL ( p = .01), but not the REM group ( p = .73). Men’s performance in REM group showed no significant difference to CTL group ( p = .20). Conclusion These findings not only show that it is possible to potentiate the consolidation of a motor memory trace during sleep but also strongly support the proposal that the association between stage 2 sleep and motor memory consolidation is critical. However, in regards to our results we can’t designate that effect to be specific to stage 2 sleep. Gender differences could be cause by several factors as (1) familiarity to the odor, (2) hormonal fluctuations (Genzel, 2012) or (3) differences in sleep and its characteristics during cuing. Acknowledgements Ovidiu Lungu, Bradley King, Arnaud Bore.