Some preteens have no trouble getting a full night's rest. Those experiencing anxiety often lie awake. The reason for both may be related to a pea-sized gland in the middle of their brains.
Researchers at FIU revealed a surprising biological link between brain structure, sleep quality and anxiety in 10-to-13-year-olds in a new study published in Scientific Reports. It reveals that while a larger pineal gland typically signals better sleep, it can actually predict worse sleep quality for preteens with high anxiety.
The study was led by FIU professor of psychology Aaron Mattfeld, a cognitive neuroscientist who studies learning and memory, alongside FIU alumnus Franco Fuertes. They used high-resolution MRI scans and overnight sleep lab monitoring to examine preteen brains.
The team determined that 50 to 60% of the preteens had pineal cysts: fluid-filled structures containing cerebrospinal fluid that do not produce hormones. Researchers separated these non-functional cysts from the parenchyma, the melatonin-producing tissue, to isolate the active gland.
While the presence of cysts had no effect on the preteen's anxiety levels, the volume of the melatonin-producing parenchyma showed a surprising contradiction. Researchers initially predicted that a larger pineal gland meant more melatonin and better sleep outcomes. However, this only proved to be true for the preteens with low anxiety. For highly anxious preteens, the larger pineal gland meant it took them longer to fall asleep and their sleep was less efficient. This contradiction was the most surprising finding for Mattfeld.
"If your anxiety is elevated and you have a larger pineal gland, you're going to have worse sleep outcomes than if you are high anxiety with a small pineal gland," Mattfeld said.
While the exact reason for this change in anxious preteens remains under investigation, the team hypothesizes that chronic stress might either change the pineal gland's cellular architecture or disrupt how the brain receives sleep signals.
Researchers specifically targeted 10-to-13-year-olds because this age marks a critical window just before internalizing disorders, such as social phobia and generalized anxiety, typically spike. During these years, the brain undergoes massive structural rewiring, strengthening critical white matter pathways and reorganizing neural connections. Simultaneously, surging sex hormones interact with receptors throughout the brain and pineal gland — the tiny structure in the brain that regulates the natural sleep-wake cycle — altering melatonin release. In addition, preteens experience a natural biological shift in their internal clock that pushes them to stay up later and sleep in. While scientists and health advocates have pushed for later school start times to align with this natural shift, policy has not been implemented. Mattfeld noted that allowing kids to follow their biological clock would likely improve their mental, physical and educational outcomes and warns that disrupting sleep impacts immune, digestive and neural health.
This discovery originated when Fuertes, then an undergraduate chemistry major volunteering in Mattfeld's lab, expressed an interest in the brain's melatonin system. Encouraged by Mattfeld to formulate his own research, Fuertes began manually segmenting anatomical brain scans of preteen participants and noticed something unexpected: dark, fluid-filled pockets inside the pineal gland.
Working in specialized sleep labs at Nicklaus Children's Hospital, researchers also monitored brain waves overnight, finding that anxious kids experience shorter, more disrupted Rapid Eye Movement (REM) sleep. During normal REM sleep, the brain acts as a night shift, clearing out metabolic waste and processing emotional memories. When REM sleep is broken up, that crucial emotional reset gets cut short.
Mattfeld warned that sleep problems are often early warning signs that appear long before a mental health condition is diagnosed. Over time, chronic sleep disruptions prevent the brain from flushing out daily waste, potentially contributing to conditions like Alzheimer's disease, Parkinson's disease or frontotemporal dementia later in life.
Supported by federal grant funding, the FIU team is currently following 200 children as they transition from middle school into late adolescence to determine whether early sleep disruptions drive psychiatric conditions. The team aims to secure additional funding to follow the group into their 20s while developing intervention strategies for kids struggling with sleep health.
Moving forward, both researchers hope their findings encourage pediatricians to routinely ask young patients about sleep and prompt families to think of sleep as vital for optimal health.
While an occasional bad night of sleep is normal, when it becomes a pattern — like consistently staying up late gaming or scrolling social media — it can have long-term consequences for mental, cardiovascular and cognitive health.
Mattfeld added, "My hope is that this data establishes sleep not just as something we need to do, but holding it to the exact same standard as cardiovascular health or obesity. When you don't treat sleep with that gravity, it messes up your biology and sets patterns that are hard to break."
For parents navigating preteen sleep struggles, Mattfeld emphasizes that consistency is key. Keep regular sleep schedules, maintain a cool and screen-free bedroom and seek behavioral therapy rather than over-the-counter supplements if issues persist.
"We need to help kids find that 'Goldilocks' amount of sleep," Mattfeld said, "because the brain is doing remarkable, necessary work while they rest."
