Sleep, Menstrual Cycle & Memory
Sleep plays a vital role in the consolidation of memories. In fact, during NREM stage 2 sleep, there are short bursts of high amplitude electrical activity called sleep spindles, and it’s these spindles that are electrophysiological markers for sleep-dependent memory consolidation. In the scientific literature, sleep spindles are also considered biological characteristics for general cognitive abilities. Research suggests that hormonal changes across the female menstrual cycles alter sleep architecture, with evidence showing NREM2 sleep is higher during the luteal phase than the follicular phase. Furthermore, studies indicate that women taking oral contraceptives have more NREM2 in the active phase when supplementing with exogenous hormones than the non-active placebo phase and in those with naturally occurring menstrual cycles. However, limited studies have investigated the relationship between sleep spindle characteristics, menstrual cycle phase, oral contraceptives, and sleep-dependent memory consolidation.
This study took 62 females in three different groups of women: (1) naturally cycling women in the luteal phase (characterized by a high endogenous progesterone level), (2) cycling women in the follicular phase (characterized by a low endogenous progesterone level, and (3) women using OCs (characterized by a low endogenous progesterone level but with potent synthetic progestins). Sleep spindle density and salivary progesterone were measured during an adaptation and an experimental night. In addition, a word pair association task preceding the experimental night followed by two recalls (pre-sleep and post-sleep) was performed to test declarative memory performance.
Before sleep, there was no significant difference between all three groups regarding intelligence assessed in the cognitive performance tasks. However, there was a positive effect of sleep on memory consolidation after a learning task. It is more pronounced in women using OCs and naturally cycling women during the luteal phase than naturally cycling women during the follicular phase.
Interestingly, these data also aligned with higher sleep spindle density in naturally cycling women during the luteal phase than women during the follicular phase and those using OCs compared to naturally cycling women in the follicular phase. These findings suggest that menstrual cycle oscillations in progesterone and the application of synthetic sex hormones modulate fast sleep spindle density.
Finally, the data revealed a highly significant change in memory performance in those groups (OC’s and Luteal Phase) where fast spindle density was increased overnight compared to the follicular group with significantly lower spindle density and no change in the overnight memory performance. Therefore, menstrual cycle oscillations of the sex hormone progesterone and synthetic sex hormones influence fast sleep spindle density and thus may alter sleep-dependent memory consolidation.
What does this mean for women on OC’s and during their menstrual cycle?
What you do have to remember is that we can’t compare apples to oranges here. This study was a tight-knit group of women who went through vigorous inclusion criteria. Therefore, it does not reflect the general population of a female who may be taking OC’s that are not progestin dominant. Nor does it consider other hormones that may vary between individuals, such as estrogen and testosterone, as well as neurochemicals such as dopamine and serotonin, all of which play a role in cognitive performance and memory recall.
However, it suggests that for women with naturally occurring menstrual cycles, it could be of additional benefit to time tasks that involve recalling information such as examinations or presentations during the luteal phase if possible and in their control. Not to say that it’s necessary but from a cognitive performance perspective knowing this information could be helpful.
Plamberger, C. P., Van Wijk, H. E., Kerschbaum, H., Pletzer, B. A., Gruber, G., Oberascher, K., … & Hoedlmoser, K. (2020). Impact of menstrual cycle phase and oral contraceptives on sleep and overnight memory consolidation. Journal of Sleep Research, e13239.