Why learning gets tougher with age: U.S. study

Tue May 24, 2011 6:07pm EDT
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By Julie Steenhuysen

CHICAGO (Reuters) - The middle-aged brain is not as nimble as it used to be because of all the stress it has endured, a study released on Tuesday showed.

U.S. researchers said stress causes nerve cells in a part of the brain needed for learning to shrink and lose plasticity -- the ability to quickly form connections called synapses.

Younger animals can recover from this but older animals start losing this ability beginning in middle age.

The findings add new understanding to the process of aging, and may help explain why some people decline more quickly than others.

"We suspected that these nerve cells would be altered by age but the loss of synaptic plasticity in the context of life experience has profound implications for age-related cognitive decline," John Morrison of the Mount Sinai School of Medicine, whose study appears in the Journal of Neuroscience, said in a statement.

For the study, Morrison and colleagues studied young, middle-aged and elderly rats who were placed in a confined area for several hours, causing the release of stress hormones that bring about nerve cell changes in the prefrontal cortex -- a part of the brain used in learning.

The team then studied changes in a part of the nerve cells called spines that are used to form synapses. When they looked under a microscope, they saw changes in the spines of the young rats, showing they were able to adapt to the stressful experience. There were few changes in the spines in middle-aged rats and none in the oldest rats.