Various studies have described that social isolation in childhood and adolescence has negative effects on brain function and sociability in adulthood, but the mechanisms responsible for this have been little understood until now.
A study1,2 published in autumn 2020 in the journal Nature Neuroscience describes for the first time which specific neuronal pathways are involved for essential sociability later in life, and how their development is significantly influenced by social experiences in childhood and adolescence.
Social isolation is increasingly coming to the fore as a major risk factor for cognitive and mental health problems. Even though we are becoming more digitally networked, young people are experiencing a growing sense of isolation.
As part of a major survey conducted by the Mental Health Foundation in cooperation with the Cochrane Mental Disorders Group, a representative sample of 2,522 young people aged 16 to 25 in the UK was surveyed.3
One quarter (25%) of them said that they often had too little company, 25% often felt excluded and 27% felt isolated. Only one in two (54%) said they were able to talk to others about their feelings. Many try to identify problems in silence by themselves, in solitude. Only one in seven (14%) said yes when asked if they had an adult confidant they could turn to for advice or support. A fifth (21%) felt that the environment in which they lived was a burden on their mental health. Only just over half (55%) of those surveyed were confident about knowing where they could seek help in the event of mental stress, and only a third (34%) were confident that they would get the support they needed there.
This survey took place in August 2019. Once the COVID-19 crisis led to the implementation of social distancing measures and school closures in many countries, it is conceivable that these figures may have changed in the meantime.
In the murine model, scientists have now been able to identify a specific population of neurons that appear to play a central role in normal social interactions in adulthood, and which are particularly vulnerable to social isolation during childhood.2 These are located in the prefrontal cortex, a brain area that plays a key role in the regulation of social behaviour. From the medial prefrontal cortex (mPFC), these neurons project into the posterior paraventricular thalamus (pPVT), a brain region that transmits signals to various components of the reward system.
Two weeks of social isolation in mice freshly weaned from their mothers meant that this circuit did not work in adult social interactions because the excitability of the corresponding neurons in the prefrontal cortex was significantly reduced. At the same time, this circuit received more inhibitory input.
In normal adult animals, the researchers were able to induce social behaviour disorders by drug or optogenetic inhibition of this pathway. In the mice that had experienced isolation at a young age, however, the deficits in social behaviour were reversible by stimulating these neural pathways, and social interactions could be increased.
If these findings are confirmed in humans, the authors see a potential key to therapies for psychiatric disorders in which isolation plays a role. But the most important message is certainly to prevent mental health problems in children and young people. Early life experiences, the environment, the exploration of one's own identity, the stresses and strains young people face when they leave school or enter the world of work all make up a period that is crucial for mental development and health.
"Having supportive families, friends and communities; the ability to understand, talk about and deal with emotional challenges; adults to turn to and who understand how they feel [...]; all of this can promote and protect good mental health from childhood to adolescence and beyond," concludes the Mental Health Foundation report.4
References:
1. Researchers discover a specific brain circuit damaged by social isolation during childhood: Study in mice shows long-lasting effects and points the way to potential treatments. ScienceDaily https://www.sciencedaily.com/releases/2020/08/200831112345.htm.
2. Yamamuro, K. et al. A prefrontal–paraventricular thalamus circuit requires juvenile social experience to regulate adult sociability in mice. Nature Neuroscience 1–13 (2020) doi:10.1038/s41593-020-0695-6.
3. Hundreds of thousands of young people feel isolated, lonely and uncertain about who to turn to when experiencing mental health problems – major new report. Mental Health Foundation https://www.mentalhealth.org.uk/news/hundreds-thousands-young-people-feel-isolated-lonely-and-uncertain (2019).
4. State of a generation: Preventing mental health problems in children and young people. Mental Health Foundation https://www.mentalhealth.org.uk/publications/state-generation-preventing-mental-health-problems-children-and-young-people (2019).