Impact of Screen Time on Kids' Brains: Diverse Results

Screen time activity — watching television or videos, playing video games, or using social media — affects structural changes in the adolescent brain, compelling early findings from new research shows.

The Adolescent Brain Cognitive Development (ABCD) study is by far the largest of its kind, as it aims to recruit 11,500 9- and 10-year-olds and follow them for up to 10 years. It will include detailed information on screen media use and data from magnetic resonance imaging (MRI) brain scans every 2 years. A multivariate tool will be used to try to disentangle the effects of other environmental factors from that of screen media use.

The current report, published in the January issue of NeuroImage, focuses on baseline data from the first 4500 individuals recruited.

Vulnerable Subgroup?

In the initial cross-sectional baseline analysis, no adverse effects associated with high levels of screen activity were observed in most participants, lead author Martin P. Paulus, MD, Laureate Institute for Brain Research, Tulsa, Oklahoma, told Medscape Medical News .

But a possible adverse effect of high screen media use was observed in one subgroup: those individuals in whom the frontal brain was more immature than the posterior brain.

In this group, children who had high levels of screen media activity showed higher rates of aggressive behavior and lower levels of knowledge-based intelligence.

"The frontal brain applies an inhibitory filter to urges generated in the posterior brain. An immature frontal brain is associated with higher levels of externalizing behavior, such as aggression/bullying," Paulus said. "In this group, high levels of screen use seem to be associated with an exacerbation of this effect."

However, he noted a major caveat with the current results.

"This is just cross-sectional data and we are just reporting an association. We don't know that it is causal. It could be a reverse association — that is, those individuals who have behavioral issues engage in more screen use," he noted.

"But I would say that these are the kids to watch out for — those children who are already showing some issues with impulsivity and aggression problems. If a child is showing these issues, it might be a good idea to limit screen activity," he added.

Differences by Media Type

The investigators also found different associations for different forms of screen activity.

"This diversity of findings provides an important public health message, ie, screen media activity is not simply 'bad for the brain' or 'bad for brain-related functioning,' " the investigators write.

"Instead, future investigations will need to examine how various forms of screen media activity influence specific psychopathology and cognitive functions, and how this influences changes throughout development."

Paulus noted that the general aim of the study is to investigate whether there are any brain patterns associated with screen usage and to look at various brain factors that put children at risk of psychiatric problems and if these are associated with screen use.

The authors note that previous studies have suggested structural brain changes can be affected by environmental characteristics, such as childhood abuse and urban upbringing. These characteristics can have direct implications for brain functions, such as general cognitive ability, behavioral inhibition, and subjective ratings of empathy. In addition, these changes seem to be triggered by regional variation of gene expression having a direct impact on cortical thickness.

The investigators point out that screen media activity is among the most common recreational activity engaged in by children and adolescents but few studies have examined its effect on brain structure or function; and the studies that have been conducted have mainly been small and cross-sectional.

The ABCD study is, therefore, innovative in both its design and size.

Three Measures of Brain Structure

The study focuses on three main measures of brain structure: cortical thickness, sulcal depth (the depth of the grooves on the surface of the cortex), and gray matter volume (cortical volume).

Paulus noted that results from a cross-sectional analysis of the baseline data so far available show that more screen media use is associated with reductions in volume and thickness of the cortex, which he said reflects increased pruning of gray matter cells.

"Pruning of gray matter cells in adolescents is a sign of brain maturation and these initial cross-sectional results suggest that increased screen media use is associated with more efficient brain activity," he explained.

In the paper, the researchers report that the greatest effects were seen in the visual areas including the occipital cortex, calcarine areas, and other primary visual cortices.

"Thus, those individuals with significant exposure to activities that engage the visual system (TV or video watching, gaming, and social network activities) show structural patterns suggestive of greater maturation in the visual system (i.e., thinner cortex, reduced volume, and a more complex pattern of changes in sulcal depth)," they write.

These initial results also show little evidence that screen media activity–related brain structure differences were associated with internalizing pathology, such as increased anxiety, depression, or other avoidance or withdrawal behaviors, the investigators note.

In contrast, they did find a strong relationship to aggressive behavior.

They report that youth who had engaged in higher levels of general and social media–related screen activity, which was linked to thinner occipital cortices and smaller volume in orbitofrontal areas as well as thinner hippocampi and smaller inferior-temporal cortical volumes, showed greater levels of externalizing psychopathology.

"Crystalized Intelligence"

In terms of cognition, the researchers note the screen media activity–associated structural brain characteristics were most strongly related to crystalized intelligence, which is more dependent on experience, represents an accumulated store of verbal knowledge and skills, and is influenced by education and cultural exposure.

Higher levels of general and social media–related screen activity, which were loaded strongly on occipital and orbitofrontal areas, showed the strongest negative relationship to crystallized intelligence.

In contrast, high gaming activity, which was associated with thinner prefrontal cortices but greater orbitofrontal cortical volume, had a positive relationship to crystallized intelligence.

"These results support the general conclusion that screen media activity-associated brain characteristics are not uniformly related to better or poorer cognitive performance. Instead, specific components that affect particular brain areas contribute differentially to cognition," the investigators conclude.

The ABCD Study is supported by the US National Institutes of Health and additional federal partners. The study authors have disclosed no relevant financial relationships.

NeuroImage. 2019;185:140-153. Abstract

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