Facing adversities in early life may put people at the risk of developing negative thinking, which could lead to major depressive disorder, a study has found. The findings, published in the journal Neuropsychopharmacology, provide biological and psychological evidence to support work first proposed in the 1960s.
Researchers from the University of Bristol in the UK used a rodent model of early life adversity to show that offspring are much more sensitive to negative biases in their cognition when treated with the stress hormone, corticosterone.
The research has shown a dose of corticosterone had no effect in normal rats but caused a negative bias in the early life adversity animals. The study also found that the early life adversity rats were less likely to anticipate positive events and failed to properly learn about reward value.
These impairments in reward-related cognition are particularly interesting as one of the main features of depression is a loss of interest in previously enjoyable activities. The findings support the idea that those at risk of developing mood disorders may have impairments in the way they learn about and use their memories about how rewarding an experience has been to then guide and motivate them to repeat the activity.
The researchers suggest that these neuropsychological effects might explain why early life adversity can make people more likely to develop depression. "This study supports a wider body of literature which suggests that depression may develop from an interesting yet complex interaction between biological and psychological processes," said Emma Robinson, professor at University of Bristol.
"As we start to understand these better, we hope that the knowledge we generate can be used to better guide current and future treatments," Robinson said in a statement.
"Our larger body of work suggests that the effectiveness of current antidepressant treatments might be linked to how much a person is able to re-engage with their environment and their level of social support," she said.
"The findings also add further evidence to support the validity of this relatively new area of research into mood disorders, particularly studies using animals to understand the neurobiology of affective biases and how they contribute to normal and pathological behaviour," she added.
Studies in patients have shown that depression is linked to changes in how the person processes information particularly emotional information. People with depression have a negative view of the world which can be measured by looking at how they process information such as emotional faces and words. However, whether this causes the illness or are a consequence is not known.
The researchers developed a method to use in rodents where similar neuropsychological processes were measured. One of the tasks, the affective bias test, looked at how simple associations between a specific cue, a bowl with a specific digging substrate in it, and a reward, a food pellet, could be biased by the animal's affective state when they learn about it.
When animals learn the association in a negative affective state they remember it in a more pessimistic way whilst memories formed in a positive affective state are remembered in a more positive way.
The biases the study was able to measure in rodents correlated exactly with how these same treatments affect peoples' mood in the long-term, something which no other animal test in psychiatry has been able to achieve.