Is the ‘default mode network’ responsible for the mental health crisis in youth?

(Note: I now also wrote up this blog post as a commentary that I submitted to the editor of the journal.)

The very short answer is: no, youth mental health problems are not generally due to the default mode network (DMN). But the editorial in Current Psychiatry that claims it may be is so remarkable that it warrants a rebuttal (here the PDF).

The piece is entitled “Is the contemporary mental health crisis among youth due to DMN disruption?”. The editor, Henry A. Nasrallah, makes the point that, yes, “DMN deactivation by excessive use of social media may explain the mental health decline in youth.”

Let’s look at the theory the editor proposes about the role of the DMN in youth mental health.

1. Daydreaming vs. attention tasks

Tasks that require dedicated attention are different from tasks like daydreaming. Not susprisingly, it has been shown that different brain networks are active for these sort of tasks, and that some of the tasks (or brain regions) are negatively correlated. Specifically, DMN activity is negatively correlated with the attention network, or, as the editor puts it: “When another brain network, the attention network [..] is activated [..], DMN activity declines”. Let’s summarize the editor’s proposed causal theory so far:

(focused attention) → (reduces DMN)

This is widely supported by evidence. Next, the editor argues that “text messaging, playing video games, or continuously interacting with social media sites” are attention tasks rather than daydreaming tasks, which extends his theory to:

(social media) → (focused attention) → (reduces DMN)

He doesn’t mention math homework here, but I do want to note that school and educational activities also require focused attention rather than daydreaming. Also, a lot of the computer games I play are more day-dreamy kind of games than focused attention kind of games, but lets ignore that complication for now.

2. Underactivity of the default mode network

The editor then claims that “the DMN is enhanced by exercise, daydreaming, and sleep, activities that are common in childhood but have declined drastically with the widespread use of smartphones, video games, and social media, which for many youth occupy the bulk of their waking hours”.

No references are given for these claims, and it is not true that e.g. sleep in youth has “drastically declined” in the last 2 decades. The editor goes on to claim that “most children and adolescents can be regarded as essentially addicted to social media, text messaging, and video games.” Again, no evidence is presented to support that, and I would expect a higher scientific standard and more rigor from an editorial written by a Professor Emeritus in Psychiatry & Behavioral Neuroscience at the College of Medicine at University of Cincinnati.

Next, the editor argues that reduced DMN activation is bad, and DMN disruption is linked to all sorts of psychiatric conditions. This leads to the full theory the editor proposes:

(social media) → (focused attention) → (reduces DMN) → (causes mental health problems)

Going back to maths homework and other tasks that require focused attention, would the editor’s theory then predict that kids who play a lot of chess or read more have more mental health problems, because their focused attention tasks would disrupt their DMN?

More importantly, the core claim here is that “When another brain network, the attention network [..] is activated [..], DMN activity declines”, and that this decline is due to social media, computer games, and other attention-demanding tasks. In a surprising turn, this notion is directly contradicted by the reference the editor provides himself in the same sentence, which explains that “In schizophrenia and depression, the DMN is often found to be hyperactivated and hyperconnected.”

So I guess that then means more rather than less social media and computer games for kids, as depression treatment? I’m starting to become really confused.

The editor also then suggests that such DMN disruption resulting from social media isn’t permanent, and can be remediated via meditation and .. psychedelics (yep). Again, a brief look at the reference the editor links to reveals that there is at best shaky evidence for this: the authors conclude in the abtract that “publication bias and methodological limitations are strong concerns”, and that “further research using rigorous methods is required to definitively link meditation practice to altered brain morphology.” Oh well.

3. Biological reductionism

I’ll keep this last part shot, because I’ve written about biological reductionism previously, in a longer blog post on mental disorders as “brain disorders”, and in a recent piece on studying mental health problems as systems, not syndromes. But the argument is so wild it really warrants a brief response.

The editor suggests DMN activation as the core, causal construct for mental health problems, in both the title and the text: “DMN deactivation by excessive use of social media may explain the mental health decline in youth”. That is, if excessive social media would not lead to DMN activation, it would no longer be a problem for mental health, because it is just one way “by” which DMN is deactivated, which in turn is the cause for mental health problems. Formally, the editor suggests something like:

(social media) → (focused attention) → (reduces DMN) → (causes mental health problems)

The first step here is of course interchangeable, but the real proposed mechanism is DMN deactivation. This is a pretty wild claim, given the multifactorial nature of mental health in kids, including parents and parenting style, family dynamics, attachment style, personality traits, early traumatic experiences, stressful and adverse events like bullying, identity issues, socioeconomic status, peer support, genetic predispositions, and so on. This may come as a surprise to the editor, but … the amount of money a kid’s parents earn, and if the family can afford for the kid to eat lunch at school, which in turn can impact a kid’s mental health, has nothing to do with the DMN. In fact, most predictors of mental health problems in youth are unrelated to the DMN. And, again, trusting the work cited by the editor, there is evidence that the DMN is hyper- rather than hypo-active during episodes of mental health problems.

Personally, I think the editor has the causal system wrong. Social media may, for some, be associated with mental health problems — weight stigma, sexism, racism, and other factors may well contribute to problems. On the other hand, I’ve seen more than one advocate from the LGBTQIA+ community argue that proposed TikTok bans under 18 in conservative, rural US states would have detrimental consequences for youth mental health because social media are the place to find peers and make destigmatizing and normalizing experiences. As always for mental health, things are complicated, and simple causal mechanisms or solutions are not going to push the field forward. We’ve done that for 50 years, and very little has come of it in terms of new treatments that work for most people. And the idea to target core mechanisms in the brain is ignoring the overwhelming evidence that the strongest predictors of mental health are psychological (personality, stress, trauma) or environmental (SES, homelessness, poverty). All experiences are correlated with brain states, but the idea that therefore, targeting brain states (e.g. via medication or brain stimulation) fixes mental health problems is a non sequitur.

Overall, this editorial would not have passed peer-review of experts in youth mental health or neuroimaging. And I sort of suspect it didn’t.

PS: I wrote this up as a commentary now — a bit more formal. PDF can be found here, and I’ll paste the commentary I sent to the editor as well for your convenience.

No evidence that mental health problems in youth are due to disruption of the default mode network

In a recent editorial, entitled “Is the contemporary mental health crisis among youth due to DMN disruption?” (Nasrallah, 2023), the editor argues that “DMN deactivation by excessive use of social media may explain the mental health decline in youth”. The editor proposes that focused attention tasks such as such as “smartphones, video games, and social media” disrupt the activation of the default mode network (DMN): “When another brain network, the attention network [..] is activated [..], DMN activity declines”. The editorial then suggests that reduced DMN activity—resulting from focused attention tasks like social media—is associated with mental health problems. Increased DMN activity, on the other hand, is positive, and results from “exercise, daydreaming, and sleep”, activities that, according to the editor, “have declined drastically with the widespread use of smartphones, video games, and social media”. Finally, the editor suggests that DMN activity can be increased via interventions such as meditation and psychedelics. The proposed causal model can therefore be summarized as: focused attention tasks like social media → increased attention network → reduced DMN → mental health problems in youth. This theory is implausible, for five reasons.

First, the editor refers to the well-cited review by Whitfield-Gabrieli & Ford (2012) regarding the relationship between DMN activation and mental health problems. However, this review shows that in mental health problems like “schizophrenia and depression, the DMN is often found to be hyperactivated and hyperconnected.” This stands in contradiction with the editor’s theory of decreased DMN activity in youth with mental health problems, and would, according to the editor’s theory, call for more, not less social media use.

Second, the editor’s theory implies a substantial relationship between social media use and mental health problems. The latest umbrella review on the topic included 25 reviews, of which the majority found either ‘inconsistent’ results or only ‘weak evidence’ for a relationship (Valkenburg et al., 2022). And a study of 355358 adolescents found that digital technology use explains only 0.4% of the variance of well-being (Orben & Przybylski, 2019).

Third, there are many focused attention tasks other than videogames and social media such as reading, doing math’s homework, and playing chess. The editor’s theory suggests that the World Health Organization should refrain from global efforts to get more kids into schools, given that this would increase the amount of focused attention tasks, reduce DMN activation, and increase the amount of mental health problems.

Fourth, youth mental health problems are multifactorial, and identified predictors include “female gender, low socioeconomic status, higher stress reactivity, conduct issues, substance misuse, and problems in peer and parental relationships” (Shore et al., 2018). Given that these factors are unrelated to the DMN, under-activation of the DMN cannot “explain” the youth mental health crisis, as the editorial suggests.

To conclude, there is no evidence to support the editorial’s proposal that “DMN deactivation by excessive use of social media may explain mental health decline in youth” (Nasrallah, 2023). To answer the question in the title of the editorial, “Is the contemporary mental health crisis among youth due to DMN disruption?” No, it is not.
 
Bibliography
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