November 4, 2019

expert reaction to study on screen use and white brain matter in children

A study, published in JAMA Pediatrics, reports a possible connection between screen use and brain development in young children.  

Prof Dorothy Bishop, Professor of Developmental Neuropsychology, University of Oxford, said:

“My evaluation of this paper is based on my expertise in developmental neuropsychology, child language development and research methods. I am not an expert in paediatric brain imaging.

“The researchers have conducted a correlational study, including a measure of screen time exposure, three measures of language/literacy skills, and two measures of white matter integrity in the left and right side of the brain on a group of 47 children in the USA, aged 3 to 5 years. Brain imaging is very challenging to do with preschool children, and so this is an impressive achievement.

“Unfortunately, the study has a number of features that reduce confidence in the robustness of the findings.

1. The review of prior literature is unbalanced to emphasise adverse effects of screen time and ignore conflicting studies. For instance, two articles are cited to support the claim that overuse of screen-based media carries a risk of language delay. As an expert on language delay, I had never heard of this claim. I checked the references. The first was a conference abstract. The second was a review paper, that cited mixed evidence of benefits and risks for language development – depending on the age of the child and the nature of the screen time.

2. Although this is an impressive sample for a pediatric brain-imaging study, it is too small to give reliable estimates of effects of screen time; it is also unrepresentative of the general population, with 78% of mothers being college graduates.

3.The measure of screen time use, ScreenQ, was devised by the first author, but the items were not made available in the paper. The authors kindly provided me with a copy and explained that scores of 1-4 reflect fairly good adherence to guidelines issues by the American Association of Pediatrics for screen use. From the plots, it would seem that only 10 children met the guidelines.  This is perhaps unsurprising, as the scale does not distinguish between TV and other types of screen use. 

4. One language measure had norms for this age range (Expressive Vocabulary), and the average score was nearly one SD above average; no child had a vocabulary score in the impaired range.  A sceptic might conclude from the plots that even high levels of screen time are consistent with above average language development.

5. The abstract reports the study found significant associations between language scores and the ScreenQ, giving the impression that these are robust, whereas the main text notes that these associations are no longer significant when household income was included as a covariate. Since many readers only read the abstract, this is misleading.

6. The study was not pre-registered, making it hard to know how many analyses were conducted but not reported. The authors report significant associations between the ScreenQ and lower connectivity in some white matter tracts, but nothing is said about predicted associations between the brain measures and the language measures. These would be highly relevant to the interpretation of results; failure to report them suggests no association was found, which makes it hard to accept that the brain measures are relevant for language development.

“Overall, this is a small study on a sample of preschool children from advantaged backgrounds who show no signs of language or educational difficulties. It seems likely that the association with brain white matter connectivity reported here would not replicate if the study were repeated. Before spending large sums of money putting pre-schoolers into brain scanners, it would seem sensible to establish whether there is the postulated association between screen media use and language outcomes – especially as a robust association was not found in the current study. The study does not provide credible evidence of an adverse effect of screen time on child development, but could serve to stoke anxiety in parents who may worry that they have damaged their child’s brain by allowing access to TV, phones or tablets.”

Prof Derek Hill, Professor of Medical Imaging, University College London (UCL), said:

“This research investigates whether heavy use of digital media – “screen time” among young  children is associated with any changes in the way the  brain is “wired”. They studied brain wiring – or “connectivity” – using an advanced type of brain scanning called Diffusion Tensor Imaging.

“Their results suggest that longer screen time is associated with differences in the children’s brains detectable in the scans.  These brain differences are similar to those associated with delayed brain development for the parts of the brains involved in language and speech.

“This work is intriguing but great care must be taken interpreting the results given the emotive topic. Firstly, an association between screen time and brain wiring says nothing about causation: you can speculate that an apparent delay in brain development might be caused by high screen time but it is equally possible that lower brain developmental status increases screen time.

“These results are preliminary.  It is a small study of fewer than 50 children who are not representative of children as a whole. And the type of brain scanning used is challenging to use in young children. Finally, the researchers measured screen time from a recently developed questionnaire answered by parents. This questionnaire may not be very objective or accurate – it might pick up parental worry more than actual time using screens.

“This research is a useful contribution to the debate and should encourage further research. In particular it highlights the need for objective and accurate measurements of “screen time” and it emphasises that we need larger and longer studies to determine whether high screen time is healthy or unhealthy for our children.”

‘Associations Between Screen-Based Media Use and Brain White Matter Integrity in Preschool-Aged Children’ by John S. Hutton et al. was published in JAMA Pediatrics at 16:00 UK time on Monday 4th November. 

DOI: 10.1001/jamapediatrics.2019.3869

Declared interests

Prof Dorothy Bishop: I have no conflict of interest to declare.

Prof Derek Hill: No conflicts of interest with the research in this paper.