Researchers are linking stress in early life to developing negative thinking, which may cause major depressive disorder (MDD) in people, according to a new study.

‘This study supports a wider body of literature that suggests that depression may develop from a complex interaction between biological and psychological processes,’ says the study’s lead author Emma Robinson, professor at the University of Bristol in Britain.

[You can beat depression with a daily bath. Here’s how]

The study, published in the journal Neuropsychopharmacology, used a rodent model to show that a dose of corticosterone had no effect on normal rats but caused a negative bias in the early life adversity animals. Its findings indicated that early life adversity rats were less likely to expect positive events and failed to learn about reward value.

These impairments in reward-related cognition are particularly interesting, as one of the main elements of depression is a loss of interest in previously enjoyable activities. The researchers suggest that these neuropsychological effects explain why early life adversity makes people more likely to develop depression.