By Benedict Carey

New York Times News Service

A generation ago, parents worried about the effects of TV; before that, it was radio. Now, the concern is “screen time,” a catchall term for the amount of time that children spend interacting with TVs, computers, smartphones, digital pads and video games.

This age group draws attention because screen immersion rises sharply during adolescence, and because brain development accelerates then, too.

On Sunday evening, CBS’ “60 Minutes” reported on early results from the ABCD Study (for Adolescent Brain Cognitive Development), a $300 million project financed by the National Institutes of Health.

The study aims to reveal how brain development is affected by a range of experiences, including substance use, concussions and screen time.

As part of an exposé on screen time, “60 Minutes” reported that heavy screen use was associated with lower scores on some aptitude tests, and to accelerated “cortical thinning” — a natural process — in some children.

The data is preliminary and it is unclear if the effects are lasting or meaningful.

Does screen addiction change the brain?

Yes, but so does every activity children engage in. The adolescent brain continually changes, in response to experiences and that adaptation continues into the early to mid-20s.

What scientists want to learn is whether screen time causes measurable differences in adolescent brain structure or function, and whether those differences are meaningful.

Have any such brain differences been found?

Not convincingly. More than 100 scientific reports and surveys have studied screen habits and well-being in young people, looking for emotional and behavioral differences, as well as changes in attitude.

In 2014, scientists from Queen’s University Belfast reviewed 43 of the best designed such studies. The studies found social networking allows people to broaden their circle of social contacts in ways that could be good and bad.

The review’s authors concluded there was “an absence of robust causal research regarding the impact of social media on the mental well-being of young people.”

In short: Results have been mixed and sometimes contradictory.

Psychologists have examined whether playing violent video games is connected to aggressive behavior.

More than 200 such studies have been carried out; some researchers found links, others have not.

One challenge in studying this and other aspects of screen time is identifying the direction of causality: Do children who play a lot of violent video games become more aggressive as a result, or were they drawn to such content because they were more aggressive from the start?

Even if scientists found strong evidence of a single, measurable effect, such a clear association would not necessarily suggest there were any consistent, measurable differences in brain structure.

Individual variation is the rule in brain development. The size of specific brain regions, the rate at which those regions edit and consolidate their networks, and the variations in these parameters from person to person make it difficult to interpret findings.

To address obstacles, scientists need huge numbers of research subjects and a better understanding of the brain.

Isn’t that what the NIH study aims to address?

Yes.

The ongoing ABCD study expects to follow 11,800 children through adolescence, with annual magnetic resonance imaging, to see if changes in the brain are linked to behavior or health.

The study began in 2013, recruiting 21 academic research centers, and initially focused on the effects of drug and alcohol use on the adolescent brain. Since then, the project expanded and includes other targets such as the effects of brain injury, screen time, genetics and an array of “other environmental factors.”

The recently published paper covered by “60 Minutes” provided an early glimpse of the anticipated results.

A research team analyzed brain scans from more than 4,500 preteens and correlated those with the children’s amount of screen time (as reported by the children themselves in questionnaires) and their scores on language and thinking tests.

The findings were mixed. Some heavy screen users showed cortical thinning at younger ages than expected; but this thinning is part of natural brain maturation, and scientists do not know what that difference means. Some heavy users scored below the curve on aptitude tests, others performed well.

Clear conclusions are extremely hard to come by and complicated by the fact that a brain scan is no more than a snapshot in time: a year from now, some of the observed relationships could be reversed.

“This diversity of findings provides an important public health message, that screen media activity is not simply bad for the brain or bad for brain-related functioning,” the authors concluded.

The measured effects may be good, or, more likely, not meaningful, until further research demonstrates otherwise.

Surely screen addiction is somehow bad for brains?

It is probably bad and good for the brain, depending on the individual and viewing habits. Many people who are socially isolated establish social networks through their screens that would be impossible in person.

Disentangling negative consequences to physical brain development from positive ones will be enormously difficult, given the many other factors potentially in play.

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