Early stress tied to mental decline later

A short period of psychological stress in infancy can lead to impaired learning and memory and a decline in cognitive abilities in middle-age, according to research conducted in rats.

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

In their study, Dr. Tallie Z. Baram of the University of California, Irvine, and colleagues found that limiting the nesting material in cages where newborn 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, the researchers report in the Journal of Neuroscience.

The stress response of the body is somewhat like an airplane readying for take-off. Virtually all systems (eg, the heart and blood vessels, the immune system, the lungs, the digestive system, the sensory organs, and brain) are modified to meet the perceived danger.

External and Internal Stressors

People can experience either external or internal stressors.

However, starting in middle age, the rats that endured early-life stress began to exhibit deficits in their ability to remember the location of objects they had seen before. They also had trouble recognizing objects that they had encountered on the previous day. These difficulties worsened as the rats grew older, and developed much more rapidly than in rats that were raised from the first week of life in a typical nurturing environment.

"The cellular bases for the cognitive difficulties were a result of change in the fine structure of brain cells, which impaired their ability to enhance their communication, as normally happens during the process of learning," Baram said in an interview with Reuters Health.

Baram noted that over 50 percent of the world's children are raised under stressful conditions. "While it has been suspected that early life stresses can lead to later cognitive impairment, it is not possible to affirm this suspicion in human studies, because the genetic background of children or other confounders make these analyses too complex," the researcher said.

"Over the last decade we have learned a tremendous amount how our genes shape our brain," Baram explained. "Now we need to also enhance our understanding of how experience and environmental signals, particularly early in life, influence our cognitive function and our behavior for life."

SOURCE: Journal of Neuroscience October 12, 2005.