The study, conducted in rats, is believed to be the first to show that early life emotional stress initiates a slow deterioration of brain-cell communication in adulthood. These cell-signaling deficits occur in the hippocampus, a brain region involved in learning, storage and recall of learned memories.

"The loss of cognitive function later in life is probably a result of both genetic and environmental factors," says study leader Dr. Tallie Z. Baram, the Danette Shepard Chair in Neurological Sciences. "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."

Faulty Communications

Baram, post-graduate researcher Kristen Brunson and colleagues found that limiting the nesting material in cages where neonatal rats lived with their mothers led to emotional stress for both mothers and pups. All evidence of this stress disappeared by the time the pups reached adulthood.

However, starting in middle age, these "graduates" of early life stress began to exhibit deficits in remembering the location of objects they had seen before, as well as difficulty recognizing objects they had encountered on the previous day.

As the rats grew older, their problems worsened, and they declined much more rapidly than rats raised for their first week of life in a typical nurturing environment.

The researchers teamed up with Gary Lynch, a UCI professor of psychiatry and human behavior and an expert on learning and memory, to understand the effects early life stress had on the brain-cell activity in the rats. They found that the mechanism responsible for a normal increase in brain communication through synapses, considered to be the cellular basis for learning and memory, was faulty in the middle-aged rats who had been exposed to early life stress.

In testing these cellular abnormalities, the researchers recorded the electrical activity of brain cells, which appeared normal in young adult rats exposed to early life stress, but became very disturbed as they reached middle age. These changes in brain-cell activity were consistent with the rats' behavioral changes.

Fifty Percent of the World's Children

More than 50 percent of the world's children are raised under stressful conditions, according to UNESCO. While it has been suspected that early life stress can lead to later cognitive impairment, this suspicion has not been confirmed in human studies because children's genetic background or other confounders make such analyses too complex.

The current study shows that early stress itself is responsible for the cognitive decline. Understanding the cellular basis for how deficits in brain-cell communication occur may permit researchers to pinpoint the molecules involved and to design medicines that target the problem.