Name: measuring neural mechanisms underlying sleep-dependent memory consolidation during naps in early childhood
Uploaded: 2019-10-02T13:00:00
Description: Watch this Scientific Journal Video about Measuring Neural Mechanisms Underlying Sleep-Dependent Memory Consolidation During Naps in Early Childhood at JoVE.com

The authors would like to thank the Neurocognitive Development Lab at the University of Maryland, College Park and the Somneuro Lab at the University of Massachusetts, Amherst for assistance with this project. Funding was provided by NIH (HD094758) and NSF (BCS 1749280) to TR and RS. Representative results were funded by NIH HL111695.

Prior to beginning any research procedures, written consent should be obtained from the parent and verbal consent should be obtained from the child for all study procedures.
NOTE: See Figure 2 for an overview of the procedures.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/60200/60200fig2.jpg" /> 
Figure 2: Overview of protocol. Each square represents one day. <a href="https://www.jove.com/files/ftp_upload/60200/60...

<ol>
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G., Huber, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-density+sleep+electroencephalogram+study.">High-density sleep electroencephalogram study.</a> Journal of Neuroscience. 30 (40), 13211-13219 (2010).</li><li>Backhaus, J., Hoeckesfeld, R., Born, J., Hohagen, F., Junghanns, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immediate+as+well+as+delayed+post+learning+sleep+but+not+wakefulness+enhances+declarative+memory+consolidation+in+children.">Immediate as well as delayed post learning sleep but not wakefulness enhances declarative memory consolidation in children.</a> Neurobiology of Learning and Memory. 89 (1), 76-80 (2008).</li><li>Wilhelm, I., Diekelmann, S., Born, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sleep+in+children+improves+memory+performance+on+declarative+but+not+procedural+tasks+TT+-+Bei+Kindern+verbessert+Schlaf+die+Ged&#228;chtnisleistung+f&#252;r+deklarative+aber+nicht+f&#252;r+prozedurale+Aufgaben.">Sleep in children improves memory performance on declarative but not procedural tasks TT - Bei Kindern verbessert Schlaf die Ged&#228;chtnisleistung f&#252;r deklarative aber nicht f&#252;r prozedurale Aufgaben.</a> Learning and Memory. 15 (5), 373-377 (2008).</li><li>Seehagen, S., Konrad, C., Herbert, J. S., Schneider, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Timely+sleep+facilitates+declarative+memory+consolidation+in+infants.">Timely sleep facilitates declarative memory consolidation in infants.</a> Proceedings of the National Academy of Sciences. 112 (5), 1625-1629 (2015).</li><li>Kurdziel, L., Duclos, K., Spencer, R. M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sleep+spindles+in+midday+naps+enhance+learning+in+preschool+children.">Sleep spindles in midday naps enhance learning in preschool children.</a> Proceedings of the National Academy of the Sciences of the United States of America. 110 (43), 17267-17272 (2013).</li><li>Kurdziel, L. B. F., Kent, J., Spencer, R. M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sleep-dependent+enhancement+of+emotional+memory+in+early+childhood.">Sleep-dependent enhancement of emotional memory in early childhood.</a> Scientific Reports. 8 (12609), 1-10 (2018).</li><li>Desrochers, P. C., Kurdziel, L. B. F., Spencer, R. M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Delayed+benefit+of+naps+on+motor+learning+in+preschool+children.">Delayed benefit of naps on motor learning in preschool children.</a> Experimental Brain Research. 234 (3), 763-772 (2016).</li><li>Maldonado, C. C., Bentley, A. J., Mitchell, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+pictorial+sleepiness+scale+based+on+cartoon+faces.">A pictorial sleepiness scale based on cartoon faces.</a> Sleep. 27 (3), 541-548 (2004).</li><li>Stern, R. A., Arruda, J. E., Hooper, C. R., Wolfner, G. D., Morey, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visual+analogue+mood+scales+to+measure+internal+mood+state+in+neurologically+impaired+patients:+Description+and+initial+validity+evidence.">Visual analogue mood scales to measure internal mood state in neurologically impaired patients: Description and initial validity evidence.</a> Aphasiology. 11 (1), 59-71 (1997).</li><li>Plihal, W., Born, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+early+and+late+nocturnal+sleep+on+indicators+of+procedural+and+declarative+memory.">Effects of early and late nocturnal sleep on indicators of procedural and declarative memory.</a> Journal of Cognitive Neuroscience. 9 (4), 534-547 (1997).</li><li>Donohue, K. C., Spencer, R. M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+re-exposure+to+environmental+sound+cues+during+sleep+does+not+improve+memory+for+semantically+unrelated+word+pairs.">Continuous re-exposure to environmental sound cues during sleep does not improve memory for semantically unrelated word pairs.</a> Journal of Cognitive Education and Psychology. 10 (2), 167-177 (2015).</li><li>Wilson, J. K., Baran, B., Pace-Schott, E. F., Ivry, R. B., Spencer, R. M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sleep+modulates+word-pair+learning+but+not+motor+sequence+learning+in+healthy+older+adults.">Sleep modulates word-pair learning but not motor sequence learning in healthy older adults.</a> Neurobiology of Aging. 33 (5), 991-1000 (2012).</li><li>Wamsley, E. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduced+sleep+spindles+and+spindle+coherence+in+schizophrenia:+Mechanisms+of+impaired+memory+consolidation?.">Reduced sleep spindles and spindle coherence in schizophrenia: Mechanisms of impaired memory consolidation?.</a> Biological Psychiatry. 71 (2), 154-161 (2012).</li><li>M&#246;lle, M., Bergmann, T. O., Marshall, L., Born, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fast+and+slow+spindles+during+the+sleep+slow+oscillation:+Disparate+coalescence+and+engagement+in+memory+processing.">Fast and slow spindles during the sleep slow oscillation: Disparate coalescence and engagement in memory processing.</a> Sleep. 34 (10), 1411-1421 (2011).</li><li>Acebo, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sleep/wake+patterns+derived+from+activity+monitoring+and+maternal+report+for+healthy+1-+to+5-year-old+children.">Sleep/wake patterns derived from activity monitoring and maternal report for healthy 1- to 5-year-old children.</a> Sleep. 28 (12), 1568-1577 (2005).</li><li>Acebo, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimating+sleep+patterns+with+activity+monitoring+in+children+and+adolescents:+How+many+nights+are+necessary+for+reliable+measures?.">Estimating sleep patterns with activity monitoring in children and adolescents: How many nights are necessary for reliable measures?.</a> Sleep. 22 (1), 95-103 (1999).</li><li>Geiger, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+sleep+EEG+as+a+marker+of+intellectual+ability+in+school+age+children.">The sleep EEG as a marker of intellectual ability in school age children.</a> Sleep. 34 (2), 181-189 (2011).</li><li>Wagner, U., Gais, S., Born, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emotional+memory+formation+is+enhanced+across+sleep+intervals+with+high+amounts+of+rapid+eye+movement+sleep.">Emotional memory formation is enhanced across sleep intervals with high amounts of rapid eye movement sleep.</a> Learning and Memory. 8, 112-119 (2001).</li><li>G&#243;mez, R. 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This article describes how to investigate sleep-dependent consolidation of declarative memory during naps in early childhood. Methods include behavioral assessment of memory across nap and awake conditions, actigraphy and parent-report to assess sleep cycles, and PSG to assess sleep architecture. This unique combination is critical for assessing memory, characterizing sleep cycles, and examining the neural mechanisms underlying the benefit of sleep on memory. Representative results indicate that learning and memory were ...

Given sleep&#39;s prevalence in our daily routine, it is important to understand its function. Studies with this objective require precise measurement of sleep. Polysomnography (PSG) is the gold-standard measure of sleep. PSG allows for objective, quantitative measurement of sleep with high temporal resolution and can be useful for both research and clinical purposes. PSG is a combination of physiological recordings. At minimum, a PSG montage includes the following measures: electroencephalography (EEG), electrooculography (EOG), and electromyography (EMG). These measures assess electrical potentials from the brain, the eyes, and muscles respectively, and allow for classification of sleep stages (see Figure 1). Other measures, such as electrocardiography (ECG), respiration, and pulse oximetry may be included to identify the presence of disordered sleep.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60200/60200fig1b.jpg" /> 
Figure 1: Example electrode placement and description of activity recorded via PSG. <a href="https://www.jove.com/files/ftp_upload/60200/60200fig1blarge.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
PSG allows sleep to be characterized into four distinct sleep stages: non-rapid eye movement (non-REM) stage 1 (nREM1; 4&#8722;7 Hz), non-REM stage 2 (nREM2; 12&#8722;15 Hz), and non-REM stage 3 (more commonly known as slow wave sleep [SWS]; 0.5&#8722;4 Hz), and rapid-eye movement (REM) sleep. nREM1 marks sleep onset, and is identified based on reduced muscle tone in the EMG recoding and mixed amplitude EEG oscillations relative to the alpha observed in resting wake. This is followed by nREM2, which can be distinguished by the presence of sleep spindles (short bursts of sigma frequency activity; 11&#8722;16 Hz) and K-complexes (single slow-waves that stand out from the surrounding activity) in the EEG. SWS is characterized by distinct slow-frequency high-amplitude EEG oscillations. REM sleep is characterized by fast low-amplitude oscillatory brain activity very similar to that observed during wake. However, what distinguishes REM sleep from wake is that it is also characterized by phasic rapid eye movements (hence the moniker REM) and muscle atonia. Over the course of a sleep bout, sleep stages are experienced cyclically, at a rate of about 90 min/cycle.
Sleep also follows the circadian rhythm, with sleep bouts taking place in 24-h cycles. Sleep timing and consistency may influence sleep function and are also important to assess. Although PSG is necessary to characterize sleep stages, it is time-consuming to apply and therefore not ideal for assessing multiple sleep bouts (e.g., multiple nights of sleep, naps and overnight sleep). For this, actigraphy is beneficial. Actigraphy uses a tri-axial accelerometer, typically on the wrist, to estimate sleep based on the absence of movement. Although actigraphy cannot be used to characterize sleep stages, it has been shown to be reliable at detecting sleep onset and wake onset (including sleep fragmentation or wake after sleep onset) in a range of populations from infants1 to older adults2. Both PSG and actigraphy are preferred methods over self/parent-report measures. Self/parent-report measures are easy to administer and relatively inexpensive, however, they are also subject to bias and non-compliance. Finally, it is worth noting that these methods can be used in combination to capitalize on the strengths of each. For example, PSG can be combined with actigraphy and/or self/parent-report to obtain both overnight sleep quality as well as verification of sleep quantities or sleep-wake cycles, especially over long durations (e.g., weeks or months).
One function of sleep that has garnered particular interest is sleep-dependent memory consolidation, the processing of memories that leaves them stronger and less vulnerable to interference3. Although memory consolidation can take place during wake in children4 and adults5, there is substantial evidence that consolidation is enhanced during sleep. Past research has provided behavioral examples of sleep-dependent memory consolidation by comparing changes in memory performance following an interval of sleep (e.g., 8 pm&#8722;8 am) to changes following an equivalent interval spent awake (e.g., 8 am&#8722;8 pm). In adults, memories are protected6 or even enhanced7 following an interval of sleep while memories typically decay over an equivalent interval of wake. Controls have been employed that dissociate performance changes from circadian influences8,9,10. For example, similar benefits of sleep are observed when comparing performance over a mid-day nap to an equivalent mid-day wake period9.
Although sleep was once thought to reflect a passive process, simply protecting memories from decay or interference, modern theories suggest sleep plays a more active role and actually promotes memory through reactivations11,12,13. Support for this comes from observed correlations between behavioral measures of memory consolidation over sleep (change in memory recall after sleep compared to before sleep) and specific aspects of sleep physiology. For many declarative memory tasks, memory consolidation is associated with aspects of non-REM sleep, specifically measures of SWS or sleep spindles found in nREM2 and SWS. If sleep&#39;s role was passive protection from interference, such a correlation would not be expected; rather a correlation between time asleep (regardless of sleep stage) and performance would be expected, as more time asleep would provide more protection from interference14.
Additional support for the active role of SWS in memory consolidation is evident in studies of targeted memory reactivation. In these studies, a memory is learned in the context of a perceptual cue, for instance an odor, and recall of the memory is greater following sleep if the cue is re-presented during sleep, SWS in particular15. Although the underlying mechanism is debated16,17, one prominent theory, systems consolidation theory, contends that memories encoded in the hippocampus are stabilized in the cortex though hippocampal-neocortical dialogue. Specifically, cortical slow waves and sleep spindles, occurring in conjunction with hippocampal ripples associated with memory reactivation, support the memory transfer3.
The role of sleep in memory consolidation during development is less clear. Early childhood is a period of particular interest as children begin to transition from a biphasic (consisting of a mid-day nap and an overnight sleep bout) to a monophasic sleep pattern. Recent research suggests that this transition may reflect brain maturation18. This argument is consistent with empirical data showing developmental changes in overnight sleep (i.e., topography of slow wave activity) mirrors that of cortical maturation19.
Although there are several behavioral demonstrations of overnight sleep-dependent consolidation in children20,21 and infants22, research on the neural underpinnings of memory consolidation with mid-day sleep are just beginning to be investigated. In ground-breaking work examining the role of mid-day naps on memory in preschool children, naps were shown to protect memories of recently learned information, whereas memory was reduced (by ~12%) when children stayed awake during the nap interval23. This &#34;nap benefit&#34; was greatest in children who napped habitually (i.e., 5 or more times per week as measured with actigraphy) regardless of their age. By recording PSG during the nap, the change in memory performance across the nap period was found to be specifically associated with sleep spindle density (the number of sleep spindles per minute of nREM), suggesting nap quality (not quantity) was a critical factor in promoting memory retention (see the representative results section).
This study highlights the significance of PSG in exploring relations between sleep and memory during development. It points to the importance of characterizing sleep macro- (sleep stages) and micro- (qualities of those stages such as frequencies and the presence of spindles) structures during naps for memory consolidation. It also highlights the importance of assessing sleep rhythms (characterizing children as habitual or non-habitual nappers). Although our work has characterized the function of naps in visuospatial learning (and more recently emotional24 and procedural25 learning), many questions remain. For instance, it will be important to examine other declarative memory tasks to assess the generalizability of these findings and to assess tasks used in preschool classrooms to understand specific parameters (e.g., amount of nap benefit relative to learning) for ecologically valid tasks. Additional work will also be necessary to understand when wake is sufficient for memory consolidation. Thus, our objective is to demystify the process of measuring sleep and sleep-dependent memory consolidation in children. We provide practical tips for examining the benefit of an afternoon nap on declarative memory in typically developing preschoolers (approximately 3 to 4 years of age) using a computerized visuospatial memory task as well as methods for assessing nap habituality using actigraphy, parent-report, and nap physiology using PSG. Although these methods were developed for preschool age children who nap with varying frequency, these methods could be adapted to any age group.

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	<tbody>
		<tr>
			<td>Actiwatch Spectrum Plus Starter Kit</td>
			<td>Philips Respironics</td>
			<td>1109516</td>
			<td>Includes: Actiwatch Spectrum Plus Device, Actiware Software License, and manual</td>
		</tr>
		<tr>
			<td>Actiware software&#160;</td>
			<td>Philips Respironics&#160;</td>
			<td>1114828</td>
			<td>Alternatives may be available.&#160;</td>
		</tr>
		<tr>
			<td>Brain Analyzer</td>
			<td>Brain Products</td>
			<td>BV-BP-170-1000</td>
			<td>Alternatives may be available.&#160;</td>
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			<td>Dell Latitude 5580 Laptop</td>
			<td>Dell</td>
			<td>X5580T [210-AKJR]</td>
			<td>Laptop for running MatLab, Actiware, and RemLogic as well as storing/uploading data</td>
		</tr>
		<tr>
			<td>EC2 cream</td>
			<td>Grass</td>
			<td>12643</td>
			<td>Possible alternatives include Ten20 paste and Lic2 electride cream</td>
		</tr>
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			<td>Embla REMLogic software&#160;</td>
			<td>Natus Medical Inc.</td>
			<td>21475</td>
			<td>Alternatives may be available.&#160;</td>
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			<td>Embletta MPR PG Sys - XR - US</td>
			<td>Natus Medical Inc.</td>
			<td>12077</td>
			<td>Embletta system for PSG recordings</td>
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			<td>Embletta MPR ST + Proxy Kit</td>
			<td>Natus Medical Inc.</td>
			<td>12696</td>
			<td>Attachment to Embletta to record PSG sensors</td>
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			<td>Nuprep cleaning solution</td>
			<td>Natus Medical Inc.</td>
			<td>12643</td>
			<td>Possible alternatives may be available.</td>
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			<td>Sleep Supplies Starter Kit for Embletta MPR ST/ST + Proxy</td>
			<td>Natus Medical Inc.</td>
			<td>12643</td>
			<td>Started kit for sleeping including guaze, EC2 cream, NuPrep cleaning solution, cotton swabs and more.&#160;</td>
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measuring neural mechanisms underlying sleep-dependent memory consolidation during naps in early childhood

Sleep is critical for daily functioning. One important function of sleep is the consolidation of memories, a process that makes them stronger and less vulnerable to interference. The neural mechanisms underlying the benefit of sleep for memory can be investigated using polysomnography (PSG). PSG is a combination of physiological recordings including signals from the brain (EEG), eyes (EOG), and muscles (EMG) that are used to classify sleep stages. In this protocol, we describe how PSG can be used in conjunction with behavioral memory assessments, actigraphy, and parent-report to examine sleep-dependent memory consolidation. The focus of this protocol is on early childhood, a period of significance as children transition from biphasic sleep (consisting of a nap and overnight sleep) to monophasic sleep (overnight sleep only). The effects of sleep on memory performance are measured using a visuospatial memory assessment across periods of sleep and wakeful-rest. A combination of actigraphy and parent report is used to assess sleep rhythms (i.e., characterizing children as habitual or non-habitual nappers). Finally, PSG is used to characterize sleep stages and qualities of those stages (such as frequencies and the presence of spindles) during naps. The advantage of using PSG is that it is the only tool currently available to assess sleep quality and sleep architecture, pointing to the relevant brain state that supports memory consolidation. The main limitations of PSG are the length of time it takes to prepare the recording montage and that recordings are typically taken over one sleep bought. These limitations can be overcome by engaging young participants in distracting tasks during application and combining PSG with actigraphy and self/parent-report measures to characterize sleep cycles. Together, this unique combination of methods allows for investigations into how naps support learning in preschool children.

Using the procedures described here, Kurdziel and colleagues23 examined sleep-dependent memory consolidation during naps in preschool children. Results showed children&#39;s recall accuracy on the visuospatial memory task after a nap was better than their recall accuracy after a similar period during which they remained awake (i.e., signifying a &#34;nap benefit&#34;, Figure 4). Moreover, those who spent the prior day in the wake condition did not ...

Watch this Scientific Journal Video about Measuring Neural Mechanisms Underlying Sleep-Dependent Memory Consolidation During Naps in Early Childhood at JoVE.com

Measuring Neural Mechanisms Underlying Sleep-Dependent Memory Consolidation During Naps in Early Childhood

This protocol describes methods used to examine neural mechanisms underlying sleep-dependent memory consolidation during naps in early childhood. It includes procedures for examining the effect of sleep on behavioral memory performance, as well as the application and recording of both polysomnography and actigraphy.

Sleep is critical for daily functioning. One important function of sleep is the consolidation of memories, a process that makes them stronger and less ...

This protocol allows for the measurement of sleep-dependent memory consolidation in children and provides a practical approach for examining the benefit of napping on declarative memory in typically developing children. Results from this technique will have implications for early childhood education, as they will provide empirically based recommendations for nap lengths in preschool classrooms. The main advantage of this method is that it can be used to assess both sleep distribution and sleep architecture, which provide data regarding brain states that support memory consolidation.Although these methods were developed for examining memory consolidation during naps in preschool-age children, they can be adapted for use with any age group and for overnight sleep bouts. Proper electrode site measurement and preparation are critical for achieving low impedances and high-quality data, which can be difficult in preschool children. Demonstrating the procedure with Tamara Allard will be Arcadia Ewell and Benjamin Weinberg, research assistants in the laboratory.After explaining the procedure to the child and parent using age-appropriate materials, have the child engage in a quiet activity. Using a flexible tape measure and china marker, measure the distance from the inion to nasion, and place a mark at the halfway point. Measure the distance from the preauricular notch on one ear to the preauricular notch on the other ear, and place a mark at the halfway point.The intersection of these two marks is the reference point, or CZ.Measure 10%of the inion to nasion distance up from the inion and 10%of the preauricular notch to preauricular notch measurement from this point on either side. Then make the O three marks on one side and the O four mark on the other. Measure out 20%of the preauricular notch to preauricular notch measurement from the reference point on either side of the head, and make the C three and C four marks on each side.Measure 20%of the inion to nasion distance up from the reference point, and measure out 20%of the preauricular notch to preauricular notch measurement from this point on either side. Then make the F three and F four marks on each side of this point. When all of the marks have been placed, use an alcohol swab to clean the first electrode location before using a slightly abrasive gel to exfoliate the skin.Remove any residual cleaning material, and fill an electrode with electrode cream. For electrodes being placed where hair is present, apply an additional drop of electrode cream to a gauze square, and place the gauze on the back of the electrode. Place the electroencephalography electrodes on each marked location on the scalp, on each mastoid, and in the center of the forehead.Place the right electrooculography electrode adjacent and slightly superior to the outside of the right eye, and place the left electrooculography electrode to the outside and slightly inferior to the left eye. Place one electromyography electrode on the right cheek, just above the smile line, and have the child say the word milk out loud while feeling for the location at which the muscle contractions in the neck and chin are maximal, to place a second electromyograph electrode on the left side, just above where the chin meets the neck, adjacent to the esophagus. When all of the electrodes have been placed, attach the electrodes to the recording device, and initiate the recording to ensure that all of the electrodes pass the impedance test.To administer the encoding phase of the visuospatial memory task, set out an age-appropriate number of to-be-remembered stimuli, and direct the child to identify each image by name. Instruct the child to remember the location of each image within the grid, and replace the cards with blank images. Then present the images one at a time, and ask the child to identify the previous location of the image within the grid, informing the child whether or not the correct location was indicated.After the child has reached a threshold of 75%correct image identification, administer the immediate recall phase. Present the images again one at a time, and ask the child to recall the corresponding location without providing visual or verbal feedback and probing each item only one time. At the conclusion of the immediate recall phase, have the child use the restroom before initiating the child's typical pre-nap routine.Allow the child to nap in their typical nap location. Then conduct the delayed recall phase for the visuospatial memory task as previously demonstrated for the immediate recall phase approximately 15 to 30 minutes after the child wakes to avoid sleep inertia. At the end of the delayed recall assessment, use water-based spray to remove the electrodes.For electrodes applied with tape, use a cotton pad soaked with baby oil to saturate the tape before gently pulling the tape up from the corners. In this representative experiment, children's recall accuracy on the visuospatial memory task after a nap was better than their recall accuracy after a similar period during which they remained awake, signifying a nap benefit. Moreover, those who spent the prior day in the wake condition did not recover memories during overnight sleep.Of interest, the nap benefit was only significant in children who napped habitually. Moreover, performance on the visuospatial memory task was related to the data obtained from the PSG recordings during the nap. Specifically, the fewer sleep spindles recorded during the non-rapid eye movement stage two sleep was related to a better immediate recall accuracy.Importantly, there was a positive correlation between the change in recall after nap and sleep spindle density during non-rapid eye movement stage two sleep. No other measure of sleep physiology was determined to be related to memory performance. Although this paper focuses on PSG, a complete understanding of sleep-dependent memory consolidation will rely on proper administration of complementary techniques, such as actigraphy and parent report, to determine sleep cycles.To compare data obtained from the nap and wake promotion conditions, it is important to keep the conditions as similar as possible in terms of their duration and interfering, distracting content. This technique can enhance our understanding of the relationship between sleep and memory during early childhood, a period of developmental significance as children transition from biphasic to monophasic sleep patterns.

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