The causal effect of screen uses versus reading on the brain development in early adolescents

Abstract The rise of new media has greatly changed our lifestyles, leading to increased time spent on these digital platforms and less time spent reading. This shift has a particularly profound impact on children and adolescents, who are in a critical stage of brain development. Previous studies have found associations between screen use and mental health in children. However, it remains unclear whether these effects are mediated by other variables or if they directly cause the observed outcomes. Here, we utilized the ABCD dataset to examine the causal relationships between screen use and brain development (cognitive, behavioral, or neuroimaging outcomes), and tested the potential displacement effect of screen use on reading habits, based on Mendelian Randomization analysis. Our results revealed adverse causal effects of screen use on language ability and behavior (e.g. withdrawn/depressed symptoms and social problems) in early adolescents between 9 - 13 years old while reading had positive causal effects on their language ability and brain volume in the bilateral frontal and temporal regions. Interestingly, increased screen use was identified as a result, rather than a cause, of behavioral issues such as rule-breaking and aggressive behaviors. Furthermore, our analysis uncovered an indirect influence of screen use, mediated by changes in reading habits, on brain development, e.g., screen indirectly reduced brain volume by reducing reading time although no direct causal effect was found. These findings provide new evidence for a causal influence of screen use and reading habits on brain development and highlight the importance of monitoring media use and related habits change in children.