Psychological stress early in life may lead to memory loss and mental decline in middle age, research suggests.
Stress may have a long-term effect
A study on rats suggests infant stress has a negative impact on the way brain cells communicate with each other.
The researchers believe parental loss, abuse or neglect may contribute to a type of memory loss in middle age more normally seen in the elderly.
The study, by the University of California, Irvine, features in the Journal of Neuroscience.
The California team highlighted problems in the signalling mechanism between cells in an area of the brain called the hippocampus, which is known to play a key role in learning and memory.
Lead researcher Dr Tallie Baram said: "The loss of cognitive function later in life is probably a result of both genetic and environmental factors.
"While it is not yet possible to change a person's genetic background, it may be feasible to block the environmental effects, particularly of early life stress, on learning and memory later in life.
"These studies point to the development of new, more effective ways to prevent cognitive impairment later in life."
The researchers induced stress in rats by limiting the nesting material in cages containing females and their new-born young.
The young rats appeared to overcome their initial feelings of stress but during middle age started to show signs of memory lapses.
The difficulties worsened as the rats grew older and developed much more rapidly than similar problems in rats raised for the first week of their lives in a nurturing environment.
Analysis showed faults in the communication mechanism between hippocampal cells in the stressed rats as they entered middle age.
Similarly, electrical activity in the cells, while normal in youth, became increasingly disturbed as the rats grew older.
A report by the UN-body UNESCO released last year estimated that more than 50% of the world's children are raised under stressful conditions.
Early life stress has previously been linked to later cognitive impairment - but it has not yet proved possible to test the association in human studies.
Rebecca Wood, of the Alzheimer's Research Trust, said previous research had shown chronic stress and recurrent depression damaged both the immune system and brain structures that are important for memory and learning.
"This new study provides the first evidence that moderate stress in young rats causes problems when they are older in the parts of the brain that are responsible for learning and memory.
"Further research will be needed in humans but these results suggest that a period of early-life psychological stress could cause decline in memory later in life."
Mrs Wood said the same parts of the brain were affected in the early stages of Alzheimer's disease.
The Alzheimer's Research Trust is funding research to investigate whether stress contributes to the development of Alzheimer's.