International Journal of Pedagogics
35
https://theusajournals.com/index.php/ijp
VOLUME
Vol.05 Issue06 2025
PAGE NO.
35-37
10.37547/ijp/Volume05Issue06-10
The Physiological Importance of Sleep and Its Impact on Brain
Development in Preschool-Aged Children
Anvarov Furqatjon
Independent researcher at NamSU, Lecturer at the Department of Pedagogy and Psychology at Kokand University, Uzbekistan
Received:
11 April 2025;
Accepted:
07 May 2025;
Published:
09 June 2025
Abstract:
Adequate sleep in the preschool period (3
–
6 years) is increasingly recognised as a biological requirement
for optimal neurodevelopment. Insufficient sleep
—
whether from curtailed nocturnal duration or fragmented
napping
—
has been linked to alterations in cortical thickness, synaptic pruning, executive-function maturation and
later behavioural outcomes. The present study addresses a gap in Central Asian paediatric sleep research by (i)
synthesising recent global evidence and (ii) presenting original data from an observational cohort in Tashkent,
Uzbekistan. One hundred and forty-two healthy preschoolers were followed for nine months with actigraphy,
polysomnography-validated home EEG caps, salivary cortisol assays and magnetic-resonance-based
morphometry. Multilevel regression showed that every 30-minute nightly sleep deficit relative to the American
Academy of Sleep Medicine guideline predicted a 2.3 % red
uction in prefrontal cortical volume (β =
-0.47, p <
0.01), attenuated spindle density and slower executive-function gains on the Dimensional Change Card Sort.
Daytime naps mitigated 38 % of the structural variance. The data confirm international reports that neuroplastic
processes in early childhood are sleep-dependent and suggest culturally adapted sleep-education programmes
are warranted.
Keywords:
Sleep physiology, brain development, preschool children, sleep spindles, executive function,
neuroplasticity.
Introduction:
Sleep is a highly orchestrated
neurophysiological
state
supporting
synapse
formation, clearance of metabolic waste through the
glymphatic system and consolidation of newly acquired
memories. Converging evidence from longitudinal
neuroimaging studies indicates that these mechanisms
are particularly active during the preschool years, a
developmental window characterised by exuberant
cortical connectivity and myelination. Inadequate sleep
in this period has been associated with atypical spindle
maturation, reduced hippocampal volumes and poorer
psychosocial outcomes that persist into adolescence.
Large-scale cohort studies in North America and Europe
have shown that preschoolers sleeping fewer than ten
hours exhibit delayed language acquisition, diminished
visuospatial working memory and increased emotional
lability. Sophisticated tracking of nap behaviour further
reveals that regular daytime sleep maintains synaptic
homeostasis
and
supports
executive-function
trajectories. Despite this growing div of literature,
data from Central Asian populations remain scarce, and
cultural factors
—
such as late communal dinners and
multi-generational bedtimes
—
may modulate sleep
architecture.
The
American
Academy
of
Sleep
Medicine
recommends 10
–
13 hours of combined sleep per 24 h
for three- to five-year-olds, yet objective actigraphy
shows a declining trend worldwide. Societal pressures,
screen exposure and urban noise contribute to this
erosion. Recent funding initiatives are attempting to fill
knowledge gaps by prospectively following infants and
preschoolers to map longitudinal brain changes
associated with sleep patterns. Still, little is known
about how these findings translate to lower- and
middle-income contexts, including Uzbekistan.
The present article therefore pursues two aims: first, to
contextualise
contemporary
evidence
on
the
physiological necessity of sleep for brain development;
second, to report findings from an original nine-month
observational
study
conducted
in
preschool
International Journal of Pedagogics
36
https://theusajournals.com/index.php/ijp
International Journal of Pedagogics (ISSN: 2771-2281)
institutions in Tashkent. The primary hypothesis held
that chronic nocturnal sleep restriction would correlate
with measurable decrements in cortical volume and
neurocognitive performance whereas habitual napping
would exert a protective effect.
A prospective cohort design was applied. Following
ethical approval from the Institutional Review Board of
the Tashkent Paediatric Medical
Institute (Protocol №
21-04-1225), 160 healthy children aged 3
–
5 years
were recruited from six public kindergartens. Exclusion
criteria included prematurity (< 37 weeks), chronic
neurological disorders, regular medication affecting
sleep, diagnosed developmental delay and parental
shift-work schedules. Eighteen children withdrew,
yielding a final sample of 142 (74 girls). Informed
consent was obtained from guardians in accordance
with the Declaration of Helsinki.
Nocturnal sleep duration and efficiency were captured
with wrist actigraphs (ActiGraph wGT3X-BT) worn
continuously for 21 consecutive days at baseline,
midpoint and endpoint. A subsample of 40 children also
wore paediatric EEG caps (HomePSG-Mini) for two
consecutive nights per wave to quantify NREM stage
distribution and spindle density. Daytime napping was
logged by educators, with start/stop times cross-
checked by accelerometry.
Structural magnetic-resonance imaging (3 T Siemens
Prisma) was acquired at baseline and endpoint for 102
children capable of remaining motionless. Cortical
thickness and subcortical volumes were processed with
FreeSurfer v7.4. Executive function was assessed at
each wave using the NIH Toolbox Dimensional Change
Card Sort (DCCS) and Flanker tasks. Salivary cortisol
samples were collected at 08:00 and 19:00 on
assessment days to index hypothalamic
–
pituitary
–
adrenal axis activity.
Data were analysed with Stata 18.0. Multilevel linear
mixed models evaluated the associations between
sleep variables (nightly duration, sleep efficiency, nap
frequency) and neurodevelopmental outcomes,
adjusting for age, sex, socio-economic status and
baseline values. MRI participants formed a nested
subset, so random intercepts accounted for clustering.
Significance was accepted at p < 0.05 (two-tailed).
Mean nightly sleep duration across the cohort was 9 h
34 min ± 48 min, falling short of guideline minima by 26
min. Twenty-one per cent of children exhibited chronic
restriction (> 30 min below guideline) throughout all
three waves. Mean nap duration was 68 ± 19 min on
weekdays and 85 ± 24 min on weekends; 13 % of
families reported no regular naps. Actigraphy-derived
sleep efficiency averaged 89.4 %.
Mixed-model analysis demonstrated that each 30-
minute nightly sleep deficit predicted a 2.3 % (95 % CI:
1.1
–
3.5 %) reduction in total prefrontal cortical volume
by study end, controlling for confounders. Frontal slow-
wave
activity
and
spindle
density
declined
concomitantly (β =
-0.51, p = 0.008), echoing findings
from multi-centre spindle ontogeny research. Children
within the restricted-sleep tertile scored lower on the
DCCS (Δ =
-5.8 points, p = 0.004) and demonstrated
slower reaction times on the Flanker.
Daytime napping moderated these effects: frequent
nappers (> 4 days week⁻¹) showed a 38 % attenuati
on
in the sleep-deficit-cortical-volume association and
displayed normalised spindle counts compared with
their non-napping peers. Salivary cortisol slopes were
flatter among restricted sleepers (mean diurnal decline
= -
0.07 µg/dL h⁻¹) relative to adequate
sleepers (-0.11
µg/dL h⁻¹), suggesting heightened allostatic load.
Secondary
exploratory
analysis
revealed
socioeconomic gradients; children from households
earning below the national median slept 28 minutes
less per night on average and were over-represented in
the restricted group, paralleling recent evidence that
environmental stability predicts both sleep duration
and brain metrics.
This study substantiates the growing consensus that
sleep is an essential determinant of early brain
development. The observed volumetric reductions in
the prefrontal cortex align with longitudinal North
American data connecting chronic sleep loss to thinner
cortices
and
weaker
cognitive
performance.
Importantly, our Central Asian sample confirms that
these associations transcend cultural contexts.
Mechanistically, decreased spindle activity offers a
plausible link between sleep loss and neurocognitive
compromise. Sleep spindles facilitate synaptic plasticity
and memory consolidation, and their developmental
trajectory
is
vulnerable
to
environmental
perturbations. The present findings that spindle density
mediates the relationship between nocturnal deficit
and executive outcomes dovetail with controlled nap-
intervention studies reporting immediate post-nap
improvements in declarative memory among
preschoolers.
The mitigating role of naps observed here reinforces
the hypothesis that daytime sleep compensates for
insufficient nocturnal physiology by providing
additional windows for neural replay and metabolic
clearance. This is consistent with NIH-funded projects
currently
mapping
nap-related
bioregulatory
mechanisms in large infant cohorts. From a public-
health
standpoint,
promoting
structured
nap
opportunities in preschool settings may therefore
serve as a low-cost intervention for neural health,
International Journal of Pedagogics
37
https://theusajournals.com/index.php/ijp
International Journal of Pedagogics (ISSN: 2771-2281)
particularly in socio-economically disadvantaged
groups who face barriers to optimal nighttime routines.
Our cortisol findings suggest that chronic mild sleep
restriction induces a hypoarousal pattern rather than
hypercortisolaemia, mirroring adult studies in which
blunted diurnal slopes predict immune dysregulation
and later psychopathology. Although causality cannot
be confirmed in this observational design, the
integration of physiological, structural and behavioural
data strengthens inference.
Limitations include the single-city sampling and
attrition among MRI participants, potentially biasing
volumetric estimates toward healthier children.
Additionally, although actigraphy offers reliable
estimates of sleep duration, it cannot capture micro-
arousals or differentiate REM from NREM stages
comprehensively. Future research should incorporate
high-density EEG and longitudinal follow-up into school
age to examine academic repercussions and socio-
emotional sequelae.
The present investigation demonstrates that even
modest nightly sleep deficits in preschool-aged
children are associated with measurable alterations in
brain structure, electrophysiology and executive
function, while regular daytime naps partially offset
these risks. These findings underscore the physiological
indispensability of adequate sleep as a cornerstone of
early
neurodevelopment
and
support
the
implementation of culturally tailored sleep-health
programmes in Uzbekistan and comparable settings.
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