But that domestication also has forged a deep bond with humans that makes dogs particularly helpful in therapy. Interaction with dogs, Kueser said, has been found to lower blood pressure, steady rapid breathing, reduce levels of stress hormones and increase levels of calming hormones.
"There's something very primal about the companionship of a dog," Ruchman said.
The Delta Society offers a list of books, articles and research on animal-assisted therapy.
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