Irregular sleep schedules are associated with altered brain structure in youth

When teenagers shift their sleep schedules between school days and weekends, the resulting mismatch can alter the physical structure and internal communication of their developing brains. A recent study published in the journal Sleep reveals that this schedule inconsistency is linked to weaker connections and reduced volume in brain areas responsible for attention, emotional regulation, and reward processing. These brain alterations suggest that irregular sleep habits might hinder normal cognitive development and mental health in adolescents.

During adolescence, human sleep patterns undergo massive biological and social shifts. Teenagers naturally tend to stay up later due to changing hormones, but early school start times force them to wake up before they have gotten enough rest.

To catch up on lost rest, many adolescents sleep in on weekends. This creates a timing mismatch between their internal biological clock and their external social schedule.

Researchers call this phenomenon social jet lag. It is essentially the biological equivalent of traveling across multiple time zones every weekend without ever leaving home.

Previous research has linked this sleep mismatch to weight gain, poor academic performance, and mental health issues like anxiety and depression. However, few researchers have examined exactly how social jet lag physically alters the developing brain.

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Adolescence is a sensitive period for brain maturation. During this time, the brain is rewiring itself, strengthening important connections and pruning away unused ones to improve cognitive functions like decision making and emotional control.

Matthew Risner, a researcher at Boston Children’s Hospital, led a team to investigate how irregular sleep schedules might interfere with this rewiring process. Working with colleagues Eliot S. Katz and Catherine Stamoulis, Risner wanted to see if social jet lag alters the physical shape and internal communication of adolescent brains.

The research team analyzed data from more than 3,500 children who were around 12 years old. This information came from a large national project that tracks child development over time.

The adolescents answered detailed questionnaires about their sleep habits on both school days and free days. The researchers used these answers to calculate each child’s social jet lag in two different ways.

The first calculation looked simply at the shift in sleep timing. The second calculation accounted for the extra hours the adolescents slept on weekends to recover from the sleep they lost during the week.

Alongside the sleep data, the researchers examined magnetic resonance imaging scans for every participant. They looked at structural scans, which show the physical size, volume, and thickness of specific brain regions.

They also looked at resting state functional scans, which measure blood flow in the brain while a person is lying still. These functional scans allow researchers to map out brain networks.

Brain networks are groups of anatomically separated brain regions that communicate and work together to perform specific tasks. By tracking which areas of the brain activate at the same time, scientists can measure the strength of the connections between them.

The team looked at time independent connectivity, which measures the overall strength of these networks. They also looked at dynamic connectivity, which tracks how these brain networks fluctuate and coordinate their activity from moment to moment.

The researchers found that over 35 percent of the adolescents experienced social jet lag of two hours or more. They also noted that boys, Hispanic youth, Black youth, and older adolescents tended to have larger shifts in their sleep schedules.

When looking at the brain scans, the team discovered extensive associations between irregular sleep and brain organization. One major finding involved the thalamus, a deep brain structure that helps regulate the sleep and wake cycle.

Adolescents with longer social jet lag had weaker functional connections between the thalamus and the rest of the brain. This suggests that shifting sleep schedules might disrupt the brain’s ability to regulate its own biological clock.

The team also observed changes in the salience network, a collection of brain regions that helps people decide which external information deserves their attention. In teenagers with high social jet lag, this network showed weaker internal connections and lower overall resilience to disruption.

A similar pattern appeared in the dorsal attention network, which governs focused, goal directed tasks. Adolescents who shifted their sleep heavily on weekends exhibited less efficient information processing within this network.

Beyond brain communication, the researchers identified differences in physical brain structure. They measured the thickness of the cerebral cortex, the wrinkled outer layer of the brain where high level thinking occurs.

Youth with more social jet lag had a thinner cortex in several areas, including regions of the temporal lobe involved in processing sights and sounds. They also had less physical volume in deep brain structures responsible for processing emotions and rewards, such as the amygdala and the nucleus accumbens.

The team also examined the spontaneous, resting activity of these brain networks. Normally, as a child grows, the spontaneous electrical activity in their brain becomes more consistent and organized.

Social jet lag was associated with abnormal fluctuations in this resting activity. Some brain areas, like the somatomotor network which controls movement, showed unusually high variability in their activity levels.

Other areas, including the default mode network which is active during daydreaming and memory recall, showed abnormally low variability. This spatial imbalance indicates that inconsistent sleep might alter the natural trajectory of brain maturation.

Finally, the researchers tracked how information flowed from one brain region to another. They measured phase transfer entropy, a mathematical concept used to determine if activity in one brain area is driving activity in another.

They found that adolescents with irregular sleep schedules had a harder time transferring information out of the amygdala and other regions related to sensory processing. This reduced information flow could make it harder for the brain to integrate sensory input with emotional responses.

While the results are highly informative, the researchers acknowledged a few limitations to their work. First, the study only looked at the participants at a single point in time.

Because they did not track the children as they grew older, the researchers cannot definitively prove that social jet lag caused these brain changes. They can only establish that an association exists between the two factors.

Additionally, the sleep data relied on self reported questionnaires, which are generally less accurate than objective measurements from wearable sleep trackers. Future studies could use physical tracking devices to gather more precise sleep data.

Moving forward, researchers hope to observe these adolescents over a longer span of years. This would help them determine if these brain alterations persist into adulthood or if they can be reversed by adopting a more consistent sleep schedule.

Future investigations might also explore how these specific brain differences directly impact a teenager’s daily life. Connecting the brain scan data to academic test scores or psychological evaluations could reveal exactly how sleep misalignment affects real world cognitive performance.

Understanding these relationships is essential for supporting adolescent health. By identifying how irregular sleep shapes the brain, health professionals can better advocate for policies and habits that promote consistent rest.

The study, “Social jet lag has detrimental effects on hallmark characteristics of adolescent brain structure, circuit organization, and intrinsic dynamics,” was authored by Matthew Risner, Eliot S. Katz and Catherine Stamoulis.