The which-comes-first question remains, but the BYU team found "children's hippocampi were intact after the onset of abuse, but somehow there was shrinkage in the group that had reached adulthood."

The pool of subjects for further study won't be shrinking. The U.S. Department of Health and Human Services said that nationwide in 2006, some 905,000 children were victims of abuse or neglect.

"The prevalence of abuse in this country is staggering," Hedges said. "With what we have found, the effects of childhood abuse may have neurological ramifications well into adult life. Boiling it down, people should be nice to their children."

Hedges plans to examine whether PTSD relates to learning and memory deficits in a follow-up study.

Study shows potential for doing more to prevent abuse and for early identification perhaps lessening the consequences of PTSD, Hedges said.

The military spent $300 million this summer — the most it has ever spent in a single year on medical research — to do just that. It will fund 171 research projects.

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E-mail: jthalman@desnews.com