Depression is now the leading cause of disability worldwide, affecting more than 300 million people. The condition often first emerges in adolescence, a critical developmental time period when an individual experiences substantial changes in their brain structure and chemistry. A known risk factor of depression is exposure to early life stress, such as illness, parents' separation or death, or adverse family circumstances.
"Mental health disorders that first occur in adolescence are more severe and more likely to recur in later life," says Dr Anne-Laura van Harmelen from the Department of Psychiatry at the University of Cambridge, the study's senior author. "With child and adult mental health services underfunded and overstretched, it is critical that we identify new ways to build resilience, particularly in those adolescents who are most at risk for depression."
People often engage in reminiscing about past events during their everyday lives, sometimes as a strategy for lifting their mood when they feel sad. A team of researchers from the University of Cambridge and University College London set out to examine whether remembering positive experiences could prove an important way of protecting ourselves against stress when it occurs in adolescence.
To test their hypothesis, the researchers analysed data from 427 young people, average age of 14 years, from Cambridge and the surrounding area, all of whom were considered to be at risk of depression. They examined the effect of recalling positive memories on two signs of vulnerability to depression: negative self-related thoughts and high morning levels of the stress hormone cortisol. The results are published today in Nature Human Behaviour.
At the start of the experiment, all participants took part in a 'cued recall Autobiographical Memory Test'. This involved giving the participants a word - either positive or negative - and asking them to recall a specific memory related to the word. Previous studies have shown that people who are depressed find it difficult to recall specific memories, relying instead on more general recollections.
In a semi-structured interview, the participants reported on the frequency of moderate to severe negative life events in the past 12 months. In addition, they self-reported any symptoms of depression during the previous two weeks and negative self-related thoughts. The interviews were then repeated 12 months later. The researchers also took saliva samples across four days at both the start of the study and after a year to examine levels of morning cortisol.
The team found that recalling specific positive memories was associated with fewer negative self-related thoughts and with lower levels of cortisol 12 months later. In other words, remembering more specific positive events reduced their vulnerability to depression over the course of one year. Further investigation showed that recalling positive events only reduced negative self-related thoughts and depressive symptoms in response to stressful life events, but not if the adolescents had experienced no stressful life events.
"Our work suggests that 'remembering the good times' may help build resilience to stress and reduce vulnerability to depression in young people," says Adrian Dahl Askelund, the study's lead author. "This is important as we already know that it is possible to train people to come up with specific positive memories. This could be a beneficial way of helping support those young people at risk of depression."