We all know people who prefer to stay up late and sleep in, and others who naturally wake up early and feel most productive in the morning. This difference is called a “chronotype,” and it’s part of our individual biological rhythm.
Scientists have long been interested in why people have different chronotypes, and what these differences might mean for their health and behavior.
In modern life, it’s easy to stay up late—thanks to phones, streaming services, and other digital distractions. But research has shown that people who are night owls are more likely to experience mental health problems like depression and anxiety, as well as poorer physical health compared to early risers.
Now, a new study by researchers from McGill University and the Mila–Quebec Artificial Intelligence Institute, published in Nature Human Behavior, offers a deeper look at why these differences exist.
The researchers wanted to find out how a person’s brain might be connected to their natural sleep-wake habits. In other words, is there something in the brain that makes someone more likely to be a morning person or a night owl?
To answer this, the researchers used data from the UK Biobank, a large health database that includes information from hundreds of thousands of people in the UK. They focused on nearly 27,000 participants who had provided brain scans, data on their daily activity patterns (through wearable devices), and information on hundreds of physical and mental traits.
Using artificial intelligence and advanced data analysis, the team looked at three major areas of the brain: gray matter volume (which includes the brain’s main cells), white matter integrity (which helps different parts of the brain communicate), and functional connectivity (how active different regions are together).
They compared these brain patterns with people’s chronotypes and their overall health, mood, and behavior.
The results were revealing. People who identified as early birds had brain features that were different from those of night owls. These differences were especially noticeable in parts of the brain related to emotions, memory, reward, and decision-making. These included the basal ganglia, the limbic system, the hippocampus, and the cerebellum.
The researchers also noticed that these brain patterns were linked to certain traits. For example, night owls were more likely to have mood-related problems, less healthy habits, and lower levels of physical activity. Meanwhile, early birds tended to show better emotional control and overall well-being.
This study is one of the most detailed investigations of how brain structure and function relate to chronotype. It provides strong evidence that whether someone is a night owl or an early bird isn’t just about habits or lifestyle—it’s deeply tied to biology.
That said, the environment still plays a role. For instance, a night owl forced to wake up early every day for work may end up feeling tired or emotionally off balance.
In conclusion, this research highlights the importance of understanding individual differences in sleep-wake patterns. It could help explain why some people are more prone to mental health conditions and why certain treatments don’t work the same for everyone.
In the future, doctors might use this knowledge to create more personalized treatment plans or lifestyle advice—taking into account a person’s chronotype to better support their mental and physical health.
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The research findings can be found in Nature Human Behaviour.
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