Adolescent Sleep Changes and Physiology

• This review examines sleep changes and sleep physiology during adolescence
• It focuses specifically on the sleeping brain.
• Brain activity during sleep offers a unique view into adolescent cortical maturation
• Sleep actively bolsters waking cognitive abilities in adolescents.
• Sleep disruption comorbidity exists with nearly all psychiatric and developmental disorders
• Understanding adolescent sleep determinants and consequences is crucial for the developing brain.

Adolescent Sleep Behavior

• Adolescence brings new social roles and increased independence, which affect sleep patterns.
• Newly acquired autonomy, circadian timing system delays, and homeostatic sleep regulating system changes that increase tolerance for sleep pressure contribute to later bedtimes during adolescence.
• School start times mainly dictate rise times, which stay the same or get earlier.
• Using self-report or objective sleep recordings, bedtime becomes later each year during adolescence.
• Among US teens, roughly 90 minutes of sleep are lost between grades 6 (ages 11-12) and 12 (ages 17-18) on school nights
• The youngest adolescents average 8.4 hours of sleep on school nights, whereas high school seniors average about 6.9 hours.
• Data from the Youth Behavior Risk Surveillance in 2007, 2009, 2011, and 2014, two-thirds of students in grades 9–12 reported 7 hours or less of sleep on school nights.
• Teens in Southeast Asia report progressively later school-night bedtimes
• Nightly total sleep time for school nights is about 3 hours less in older adolescents compared to younger ones.
• Over a 10-12 to 15-18 year span, adolescents average approximately 9.25 hours of sleep when given ten hours of sleep opportunity, irrespective of age or maturational stage
• Sleep duration declines on school days but remains constant on weekends
• Sleep deprivation, induced by the school day, stems from environmental factors rather than biological ones.
• Understanding the consequences of chronic sleep deprivation is crucial due to a discrepancy between sleep need and acquired sleep.
• Tenth graders on a self-selected school night schedule, fell asleep in about 5 minutes, nearly half the time compared to later in the day
• Roughly 50% fell asleep and entered directly into REM sleep in under 2 minutes
• Circadian rhythm delays and reduced sleep due to earlier school start times may cause pathological sleepiness in 10th graders.
• Starting the school day tired and unprepared for social and cognitive challenges is commonplace for many teens.

Measurement and Key Principles of Adolescent Sleep

• Methods for measuring sleep include self-reports, actigraphy, and polysomnography (PSG).
• Self-reports help assess perceived sleep difficulties and daytime functioning and help inform diagnostic criteria for psychiatric conditions
• Actigraphy uses a wrist-worn, watch-like device to track sleep and waking based on motion.
• Actigraphy devices measure sleep broadly and assess it over extended durations, like weeks or months.
• Research-grade activity monitors use validated, open-source algorithms to gauge sleep, while newer commercial devices rely on proprietary software.
• Validation studies of activity monitors show mixed results regarding specificity and sensitivity.
• Though actigraphy and self-reports are valuable, polysomnography (PSG) is the main method for measuring sleep.
• Polysomnography (PSG) requires constant tracking of electroencephalogram (EEG), electrooculogram (EOG), and electromyogram (EMG).
• Physiological signals divide sleep into non-rapid eye movement (NREM) sleep, subdivided into 3-4 stages, and REM sleep.
• The EEG signal gives insights into cortical oscillations in the sleeping brain, such as slow waves and sleep spindles during NREM sleep.
• Slow waves, which occur at a low frequency (0.4 to 4.6 Hz) and have a high amplitude, mostly occur in the cortex
• Slow waves are plentiful at the start of the night, have an exponential drop during sleep, and show a rise in frequency and amplitude following sleep deprivation .
• The thalamus may help modulate slow waves and their preferential occurrence at the beginning of sleep shows their role as sleep homeostatic system markers.
• Unlike slow waves, which dominate sleep EEG activity, sleep spindles are transient oscillations that last for 1-2 seconds and have a frequency of 11-16 Hz.
• Sleep spindles are generated through thalamocortical loops and aid sleep consolidation and declarative memory systems.
• The Fourier transform computes the strength of EEG's constituent frequencies; it calculates EEG oscillations from EEG signals.
• EEG slow-wave activity (SWA) is defined as total power (µV2) in the 0.4–4.6 Hz range; spindles are summarized via total EEG power in the 11–16 Hz range.
• The spectral frequency of spindles shifts between people and throughout development.
• The frequency of the peak power measures spindle activity sensitivity to inter-individual variance.

Sleep Physiology in Adolescence

• Clear maturational changes are present in oscillatory physiology alongside sleep and circadian rhythm development.
• These trajectories are likely determined by brain anatomy maturation
• The striking change in sleep EEG is reduced EEG amplitude and power in the sleep EEG signal, starting earlier in girls and linked to pubertal maturation.
• EEG power is reduced by up to 40% from before to after puberty across EEG frequencies in waking and sleep states.
• Reduced cortical gray matter throughout adolescence can significantly drive reductions in EEG power.
• Correlations exist across an age range of cortical regions between sleep EEG power and gray matter (structural MRI)
• The age-dependent decline was seen in both measures, further supporting the reduction in sleep EEG power is caused by reductions in gray matter volume.
• The developmental progress of maximal sleep slow wave activity (spectral sleep EEG power between 0.6 and 4.6 Hz; SWA), from posterior to anterior cortical regions, was a study that measured cortical activity at a large number of cortical regions using high-density EEG
• This progression closely resembles observations from longitudinal MRI studies on regional maximal cortical gray matter volume.
• White matter volume increases as another aspect of adolescent brain development.
• Resting EEG coherence, an EEG measure of connectivity, linearly rises among adolescents similar to changes in white matter volume.
• Like the decline in sleep EEG power, this coherence increase appears across frequencies and sleep states, suggesting an anatomical component affecting coherence.
• Peak spectral spindles' frequency exhibited a rising trend over adolescence and is hypothesized to reflects cortical myelination; there is no clear data to support this.
• The rate of sleep EEG power and coherence change are not correlated, indicating two separate processes.

Sleep: An Active Role in Brain Development?

• Sleep helps sculpt the adolescent brain.
• Synaptic spine elimination occurred more often during sleep than wakefulness in adolescent mice which indicates sleep has a distinct role in adolescent brains
• Self-reported sleep duration positively correlated with bilateral hippocampal gray matter volume in structural MRI scans of 290 children and adolescents ages 5–18.
• There is an association between variability in sleep duration across 14 days and white matter integrity as measured with diffusion tensor MRI in adolescents
• Evidence is emerging on the role of sleep in brain development.

Sleep Traits and Associations with Cognition

• Sleep EEG can identify associations with metrics of cognitive aptitude
• Sleep EEG provides a target as its spectrum is stable across consecutive nights of recording yet unique to an individual.
• The form of the sleep EEG spectrum remains largely the same in adolescents for many years, in spite of cortical restructuring and maturational changes to sleep EEG strength
• Recent data suggest high heritability among sleep EEG spectrum, which makes it trait-like.
• Positive correlations exist between an intelligence quotient (IQ) and sleep spindles magnitude (power, amplitude, and density) in both children and adolescents
• Associations are uncovered between spindles and cognitive performance on tasks of executive function and response inhibition through a two-year study measuring sleep coherence and waking performance
• Increases in intra-hemispheric spindle coherence is shown for those who improved the most on tasks measuring executive function and response inhibition.
• Sleep spindles are thalamocortical loops, so their action gives key insight into cortical operation and circuit unity supporting cognitive function.

Sleep and Learning and Memory

• Manipulating sleep, specifically manipulating sleep duration can affect cognitive function.
• The restorative benefit of sleep and the detrimental impact of sleep loss were documented in adults
• Both benefits and detriments were identified using experimental protocols that targeted attention, executive function, reward sensitivity, emotional regulation, and learning and memory
• Perturbations in sleep include a daytime nap, complete sleep deprivation for one night, or sleep restriction for several days.
• Short perturbations in sleep do not gauge how shortened sleep affects long-term cognition, but offer a prime opening for experimentally examining impact of sleep loss during crucial developmental windows.
• A majority of studies on sleep-dependent cognition have targeted adults

Sleep-dependent Emotion Regulation

• Sleep impacts emotion, learning and memory
• Sleep loss increases negative mood and heightened emotional reactivity to visual scenes and faces, as well as alters emotional memory processing.
• Preliminary data imply that sleep loss negatively impact mood and emotional regulation in adolescents, following acute and chronic doses of sleep restriction
• Studies outlined used experimental manipulation of sleep over a night or two rather than actual conditions where sleep loss occurs over a long interval in adolescence and childhood
• Adolescent obstructive sleep apnea impairs learning, memory, affective and reward processing
• Chronic sleeping issues early in childhood correlate with elevated risk-taking in adolescence by a sleep-mediated deficit in working memory
• A practical question is how chronic, widespread sleep deprivation seen in teens impact essential cognitive - and emotion-regulating functions.
• High comorbidity of sleep problems exists within adolescent psychopathology, such as depression, ADHD, impulse control disorders, anxiety, and bipolar disorder.

Insufficient Sleep and Behavioral Problems in Teens

• Many studies show that insufficient sleep is linked to poor emotional functioning in teens without diagnosed psychiatric disorders.
• Insufficient sleep has been linked to depressive symptoms, hopelessness, anxiety
• Reported drunk driving, weapon carrying, fighting, contemplating suicide, attempted suicide, smoking, alcohol use, binge drinking, marijuana use, sexual risk taking, and texting while driving are significantly increased risks in high school teens reporting 7, 6, 5, or less than 5 hours a night
• There is a high relative risk of obesity with less sleep.
• Early morning school schedules make sleep more difficult for kids
• When school start times are later, sleep is enhanced, enrollment rates and attendance improve, students sleep less, symptoms of mood depression are reduced, and car accidents in teen drivers are lower.

Summary: Sleep Matters

• Research has indicated sleep has a key role in adolescent brain function and behavior.
• There is no data on unique functions in adolescent sleep compared to adults.
• Concurrent studies are needed to compare adolescents with adults and children for any overlapping neuronal benefits.
• Adolescents have distinct social, cognitive and behavioral demands, prompting a higher need for sleep during the stage.
• Synaptic homeostasis is a major theory about what sleep carries out, where slow wave activity during sleep functions to reset synapses following being awake.
• The youth's high rate of slow wave activity might come from the more synapses in children and teens.
• Assuring good sleep that is restorative and on time is critical.
• A basic level of sleep hygiene protects sleep.
• Teens whose parents set bedtimes around 10pm showed fewer depressive symptoms and thoughts of suicide
• Behavioral therapy and cognitive methods are effective, particularly for more pronounced sleep problems.
• In adolescence, treating this is important for behavioral, emotional and cognitive issues.

Conclusion

• Sleep helps with cognition.
• Public health initiatives could promote later school start times for lengthened weeknight-sleep, along with less lateness, attendance, and better grades.
• Public health measures can affect sleep, such as middle schools not beginning until 8:30 am.

Tips for Teens to Improve Sleep

• Make a sleep plan for enough time to sleep and stick to sleep plan
• Each morning, seek light to advance internal clock and help ensure earlier bedtimes
• Avoid light at evening to keep the internal clock from migrating
• Avoid activities that raise stress before you are going to relax
• Minimize devices such as cellphones at night
• Keep the weekend and weekday sleep close to the same
• Avoid caffeine after afternoon and only take short naps before 4
• Ensure time for enjoyment during the day