New research shows that disrupting teenagers’ circadian rhythms not only makes them tired, but fundamentally how their brains respond to severe mental health conditions in response to prenatal risk factors.
McGill University scientists have found that when adolescent mice are exposed to constant light, it alters their brains to process the effects of pregnant women during pregnancy, a known risk factor for schizophrenia and autism spectrum disorder. The findings challenge hypotheses about how multiple risk factors combine to influence brain development.
Accidental protection effect
Researchers expect the worst: disruption of circadian rhythms can amplify the negative effects of prenatal infection. Instead, they found something surprising.
“We think the effect will be additive,” said Nicolas Cermakian, professor in McGill’s Department of Psychiatry. “But in some cases, disruption of biological rhythms actually reduces the effects of prenatal infections. This suggests that these factors may interact in unexpected ways.”
Mice expose mice to maternal immune activation during pregnancy and then continue to be exposed during puberty (equal to permanent sunlight). Although each factor can cause problems independently, their combination creates complex, sometimes protective effects on memory, anxiety, and social behavior.
Why puberty is the most important
The timing is not random. When mental illnesses usually occur, adolescence represents a critical window, and teenagers naturally undergo a huge shift in their biological clock.
“Teenagers are vulnerable,” Cermakian explained. “Their internal clocks tend to be later than other populations, but schools still start early. Most importantly, late-night contact with screens and artificial light can further delay their biological rhythms, resulting in what we call social jet lag.”
This biological mismatch affects about 80% of people with neurodevelopmental disorders, whose sleep and circadian rhythm disruption.
Male brains are hard to beat
One of the most compelling findings of the study involved gender differences, which were not highlighted in the preliminary report. The study showed that at the molecular level, the responses between male and female mice were very different.
In the hippocampus, brain infection triggers changes in 1,055 genes in men, while only 83 genes in women under similar conditions. This huge difference helps explain why conditions like schizophrenia and autism have different effects on men and women.
The study also found that certain genetic modules were particularly associated with microglia (the immune cells of the brain), suggesting that these cells play a key role in how environmental factors reshape the developing brain.
Molecular Mystery
The researchers used advanced genetic analysis to identify specific gene networks that responded to these two factors. Many of these genes are involved in synaptic transmission (process conveyed by brain cells) and are associated with sleep disorders and neurodevelopmental status in humans.
Key findings include:
- Constant light exposure affects gene expression in neurons and microglia
- Prenatal infection mainly affects male hippocampus gene activity
- Joint exposure creates unique molecular characteristics
- Many affected genes are linked to human mental illness
The meaning of the real world
These findings are directly related to modern adolescents. Late night screen time, early schedules and artificial lighting create a perfect storm for the circadian rhythm during fragile development.
“Although more research is needed, our findings suggest that people exposed to multiple risk factors may need to pay special attention to their daily rhythm,” said Tara Delorme, his study author, as a doctoral student.
The team is now investigating whether these genetic changes in mice can reveal how the human brain develops and responds to environmental challenges.
Beyond simple addition
This study fundamentally changes scientists’ perceptions of mental health risk factors. Rather than simply increasing individual risks, the study shows that time and interaction are extremely important in determining outcomes.
For families of children with prenatal complications, maintaining a consistent sleep schedule during adolescence may be more important than previously known.
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