Early brain development relies heavily on REM sleep.
Alcohol is one of the most powerful suppressors of REM sleep. When a breastfeeding mother consumes alcohol, traces can pass to the infant, disrupting REM sleep. Chronic sleep disruption during early development has been linked to abnormal brain development and may negatively affect social and cognitive outcomes later in life.
The suprachiasmatic nucleus (SCN)—the brain’s master clock—takes time to develop. Not until around age three or four do children begin to show clear signs of being governed by a daily circadian rhythm. This helps explain why newborns don’t naturally follow the sunrise–sunset cycle.
Circadian rhythm and sleep architecture change across different stages of life:
REM sleep plays a key role in early life by helping the brain create new neurons and build neural connectivity. As children grow into adolescence, the brain’s goal shifts—from rapid growth to refinement and efficiency. During this stage, NREM sleep increases, supporting pruning and optimization of neural networks.
Interestingly, changes in NREM sleep often occur weeks or months before major cognitive and developmental milestones. This suggests that deep sleep may actively drive brain maturation, rather than simply reflecting it.
NREM sleep also develops from the back of the brain to the front. The frontal lobe—responsible for rational thinking and impulse control—is the last to mature. This may help explain why teenagers are more prone to risk-taking and less consistent rational decision-making.
As people age, NREM sleep deteriorates, particularly deep sleep. This decline may help explain why older adults often experience memory difficulties. Importantly, the brain regions most responsible for generating deep NREM sleep are among the first to show signs of aging, linking sleep quality directly to cognitive aging.