Next, we used a multivariate ANOVA (MANOVA) with group (Nap and QW) as the independent variable; performance (proportion correct at PM) in Novel, Primed, and Repeated conditions as dependent variables; and baseline performance as a covariate. Danielle Pacheco. (31) measured HF HRV during retrieval of emotional memories and reported a positive correlation with activity of the medial PFC. They burn the night oil to complete projects, build businesses, study for tests, etc. 2), and neither model accounted for a significant amount of variance in performance (model 1: Adj R2 = −0.02, P = 0.47; model 2: Adj R2 = 0.21, P = 0.18; negative variance indicated by counterclockwise angle meter). These findings present the first evidence, to our knowledge, that ANS activity may be one potential mechanism driving sleep-dependent plasticity. The autonomic nervous system (ANS) shows strong variation across sleep stages. Cai et al. A total of 90 RAT problems were compiled in the current experiment. It is therefore possible that two parallel mechanisms may facilitate performance improvement in the explicit memory condition, one during a quiet wake episode involving rehearsal or rumination on the RAT items, and the other involving memory reactivation processes during sleep. Pearson correlation coefficients (Bonferroni-corrected) were used to examine the bivariate relationship between HF HRV during sleep, minutes in each sleep stage, sleep spindles, and all performance conditions. Next, we used a MANOVA on group (Nap and QW) and performance (proportion correct at PM) in Novel, Primed, and Repeated conditions, again controlling for baseline performance. Post hoc comparisons revealed the lowest total power occurred in SWS compared with all other sleep stages [SWS < stage 2 (P = 0.001), < REM (P = 0.001)]. One theory of sleep as restorative states that the chemicals in the brain, _____, are replenished during REM sleep. For each problem, the subject has to combine or relate the three words drawn from mutually remote associative clusters (e.g., COOKIES, SIXTEEN, HEART: ______). We hypothesize that central nervous system processes that favor peripheral vagal activity during REM sleep may lead to increases in plasticity that promote associative processing. Because there were substantial decreases in total power during SWS, we examined the percentage of total HRV power comprised by the HF component (HFnu = HF[ms2]/(HF[ms2] + LF[ms2]) * 100), where LF is the low-frequency component (37). RVLM, rostral ventrolateral medulla. This session ended at 3:30 PM, and subjects were allowed to leave the laboratory. Thank you for your interest in spreading the word on PNAS. Interestingly, here and in the study by Cai et al. 3], with REM minutes (β = −0.55, P = 0.01) and sleep spindles (β = 0.51, P = 0.02) emerging as significant predictors, whereas time spent in SWS was not a significant predictor (β = −0.06, P = 0.77; Table S4). We believe that the consideration of sleep within this framework of sleep-dependent consolidation of long-term memories via hippocampal-PFC dialogue could be an important addition to this model (Fig. Descending projections from the PFC to autonomic/visceral sites of the hypothalamus and brainstem create a feedback loop allowing for bidirectional communication between central memory areas and peripheral sites (12⇓–14) (Fig. Eighty-one healthy, nonsmoking participants (age = 21.79 ± 3.29 y, 31 females) with no personal history of neurological, psychological, or other chronic illness provided informed consent, which was approved by the University of California, Riverside Human Research Review Board. 31 Some patients also report dreaming the same content throughout the night, despite intervening episodes of wakefulness. We present the first evidence, to our knowledge, that the autonomic nervous system (ANS) plays a role in associative memory consolidation during sleep. Method Data were collected in October, 2013. Further, during REM sleep, there is an increase in overall cardiac autonomic activity (24) accompanied by an increase in central control of cardiac regulatory patterns compared with NREM sleep (67). This method emphasizes consolidated sleep stages and resulted in different percentages of ECG epochs for the HRV analysis. We used a MANOVA to compare performance (proportion correct at test) between Nap and QW groups in all three RAT conditions: Novel, Primed, and Repeated. ↵1L.N.W. For the Novel condition, sleep variables did not significantly predict performance in model 1 [F(3,13) = 0.89, P = 0.47]. In this view, HRV may be a proxy measure of the level of these ongoing plasticity processes. (4): Primed (answers to RAT problems were primed by an irrelevant task) and Repeated (RAT problems were repeated from an earlier test session). 12. Descending projections from the PFC to the hypothalamus and brainstem create a feedback loop facilitating the modulation of peripheral activity by the central nervous system, including HRV. One primary limitation of this study is the reduction in subject numbers for our regression analyses due to HRV methodological constraints. In fact, HF HRV during REM was the only consistent predictor across both models. Heart rate increases and breathing becomes more irregular. PSG monitors many body functions including brain (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG) and heart rhythm (ECG) during sleep. In the Repeated condition, model 1 (sleep variables) accounted for a marginally significant amount (26%) of the variance in performance [Adj R2 = 0.26, F(3, 13) = 2.89, P = 0.08], with sleep spindles as the only significant contributor to this model (β = 0.47, P = 0.05). This allows us to dream quietly and safely throughout the night. Prior studies have established that parasympathetic/vagal activity is associated with the high-frequency component of HRV [HF HRV; 0.15–0.40 Hz (23)]. This elevated performance in nappers was likely due to random error, because the mean performance scores at baseline in the Quiet Wake (QW) group and the Novel condition for both nappers and QW subjects were similar (mean scores ∼ 0.35) (Fig. During SWS sleep, studies have reported a reduced heart rate (i.e., a lengthening of RR intervals) coupled with a reduction in overall cardiac ANS activity and a dominance of parasympathetic/vagal activity (HF HRV) compared with wake and REM (24). Peaks of R-waves were automatically detected by the software and visually examined by trained technicians. Here, we examined whether changes in cardiac ANS activity (HRV) during a daytime nap were related to performance on two memory conditions (Primed and Repeated) and a nonmemory control condition on the Remote Associates Test. Making lasting memories: Remembering the significant, Enhancement and impairment of memory processes with post-trial injections of adrenocorticotrophic hormone, Naloxone and β-endorphin alter the effects of post-training epinephrine on memory. We analyzed HRV of the R-waves series across the whole sleep/wake period using Kubios HRV Analysis Software 2.0 (MATLAB), according to the Task Force of the European Society of Cardiology and North American Society of Pacing and Electrophysiology guidelines (66). Such blood flow changes indicate the brain is healthy, according to Drew. Sleep spindles in NREM sleep were detected with an automated spindle detector that used both MATLAB routines and BrainVision Analyzer software (70). In contrast, some nondeclarative information, such as our Primed condition here, mainly rely on sleep processes (5, 44, 45). Participants had a regular sleep-wake schedule (reporting a habitual time in bed of 7–9 h per night as assessed by actigraphy), and no presence or history of sleep, psychiatric, cardiovascular, or neurological disorder determined during an in-person, online, or telephone interview. We used a hierarchical regression approach and entered the sleep variables (SWS minutes, REM minutes, and number of sleep spindles; mean-centered) into the regression first, allowing these three variables to account for variance in performance change before entering in the HRV variables (HF HRV during SWS and REM; mean-centered). Performance in all groups did not change in the Novel condition compared with baseline, whereas it improved in the Repeated condition. Interestingly, we noted that compared with baseline performance, the QW group showed a decrease in performance in the Primed condition [t(20) = −2.63, P = 0.02], an increase in performance in the Repeated condition [t(20) = 2.06, P = 0.05], and no difference in the Novel condition [t(20) = −0.09, P = 0.93]. However, after the addition of HF HRV in model 2, the contribution of sleep spindles was reduced in both Repeated and Primed models. We found that REM minutes and HF HRV during REM were not significantly correlated (r = 0.01, P = 0.99), which suggests independence between these two variables. Ten of the analogy answers served as primes for the answers to the RAT items administered in the primed condition during the PM session. Bivariate relationships between each predictor and the outcomes are reported in Table S3. Each RAT problem contains a triplet of words presented horizontally along with a blank space. Creativity and associative thinking have been thought to require the formation of “associative elements into new combinations, which either meet specified requirements or are in some way useful” (32). Instead, HF HRV during REM was a predictor (β = 0.54, P = 0.02). The subject is required to find a fourth word that serves as an associative link between these three words. Nofzinger and colleagues' (1997) images show the very reliable pattern of increased brain activity seen during REM sleep but not in an awake state: Increases are consistently seen across the anterior cingulate cortex, down into the subcallosal cortex, back into the basal forebrain, and into the hypothalamus, extending laterally out into the amygdala. Peripheral activity has been purported to affect memory consolidation via vagal afferent nerve fibers, which communicate information about ANS excitation and arousal via projections to the brainstem, which then project to memory-related areas, including the amygdala complex, hippocampus, and prefrontal cortex (PFC) (11). It is thought that excessive EMG activity in RBD reflects dysfunction of the brainstem structures responsible for muscle atonia during REM sleep.1In animals, experimental lesions in the brainstem produce increased tonic and phasic EMG activity and abnormal behaviors during REM sleep.2–5In humans, RBD can be idiopathic or associated with neurodegenerative diseases.6Follow … Copyright © 2021 National Academy of Sciences. We also analyzed 5 min of prenap wakefulness (Wake). Error bars represent ±1 SEM. Advancement in HRV measurement techniques could allow for more data retention. Ten problems were exactly the same as the AM baseline RAT problems (Repeated condition), 10 problems had the same answers as 10 (out of 30) of the AM analogies (Primed condition), and 10 problems were completely novel (Novel condition). Interplay between spontaneous and induced brain activity during human non-rapid eye movement sleep. Asterisks represent significance at P < 0.05. Norepinephrine and orexin (also called hypocretin) keep some parts of the brain active while we are awake. REM sleep showed the highest total power, which was significantly greater than SWS (P < 0.001). Due to the large amount of sleep transitions present in a daytime nap, this approach limits the total amount of data available for the regression analyses. Throughout history, psychologists and philosophers have proposed that good sleep benefits memory, yet current studies focusing on the relationship between traditionally reported sleep features (e.g., minutes in sleep stages) and changes in memory performance show contradictory findings. Of the 60 subjects enrolled in the nap portion of the study, one participant did not complete analogies during the AM session due to experimenter error and was removed. Accordingly, vagus nerve lesions have been shown to impair memory (15, 16). In the current dataset, associations initiated during the analogy task may have instantiated weaker memories that were downscaled during REM sleep (52), resulting in the inverse relationship between REM sleep and performance indicated in the current study. Proportion of variance in associative memory improvement accounted for by sleep and autonomic activity during sleep. Another drawback of the current study is the lack of NREM-only naps available for analysis (n = 8). However, the role of ANS in sleep-dependent memory consolidation has never been examined. Thus, when the arousal threshold is highest (i.e., sleep is “deepest”), the EEG shows slow-wave sleep … At 1:30 PM, nap subjects (n = 60) took a polysomnographically recorded nap for ∼90 min. No significant correlations were revealed between HF HRV in the Quiet Wake condition and performance [Novel: Pearson correlation coefficient (r) = −0.17, P = 0.48; Primed: r = −0.28, P = 0.23; Repeated: r = 0.006, P = 0.98]. Fast Fourier transform quantified the absolute spectral power in the HF (0.15–0.40 Hz) and LF (0.004–0.15 Hz) bands, and total power (a summation of HF power, LF power, and all other spectral components comprising the RR interval; measured in square milliseconds). This period of high plasticity and low sensory input (sleep) may situate REM sleep as a brain state optimized for making connections between disparate ideas, which is a principal definition of creativity (32). Together, these findings highlight vagal activity as a possible factor influencing plasticity during waking memory consolidation, yet the role of autonomic activity for sleep-dependent memory consolidation has not been examined. Sleep boosts performance in the Primed condition on the RAT. Missing and ectopic beats were corrected via cubic spline interpolation. 1). Furthermore, distinct memory manipulations of the RAT have been shown to rely on REM sleep (4). In addition, REM sleep shows both greater total ANS activity and higher parasympathetic/vagal activity compared with wake and SWS sleep (25). 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