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Release: Dec. 15, 1999

UI psychologists show flaws in imposing human qualities on animals

IOWA CITY, Iowa – Do infant rats cry? Scientists discovered 45 years ago that when separated from the nest rats emit an ultrasonic "distress call." But is this the same as a human infant crying for its mother? In a paper to be published in January in Psychological Science, a group of University of Iowa psychologists says the answer is No.

Human infants cry because they are hungry, wet, cold, or otherwise in need of attention from a parent. But rat pups cry involuntarily as a result of a physiological process, the UI team says. Mark Blumberg, a UI associate professor of psychology and primary investigator for this project, says the rat cries are a by-product of a maneuver that increases blood flow to the infant’s heart when that flow is reduced. Although the cries often also result in the rat mother retrieving the pup to the nest, Blumberg says it is important not to assume that the two are directly related.

"We can't infer the intent to communicate based on the response of the receiver," Blumberg says. "For example, although a sneezing child may prompt a parent to hand over a tissue, we don’t infer from this that the child sneezed in order to communicate to the parent that a tissue was needed."

Infant rats emit cries when they are exposed to extreme cold, which causes a significant decrease in cardiac rate. The cries are also heard after rats have been injected with clonidine, a drug that causes withdrawal of central nervous system stimulation to a number of organs, including the heart, resulting ultimately in decreased blood flow back to the heart. Based on these and other factors, Blumberg and his team hypothesized that the cry, produced by strong compressions of the abdominal muscles, might be an acoustic by-product of a physiological process that propels venous blood back to the heart.

In support of their hypothesis, Blumberg and his team were able to measure venous blood pressure after pups were treated with clonidine and show that the vocalizations were indeed associated with large increases in venous return. Based on this evidence, the cries can be understood as involuntary vocalizations that result from a physiological process. Thus, while a rat pup's cry may prompt the mother to retrieve the pup to the nest, the pup has not cried in order to seek maternal care.

"It is natural for people to attribute human thoughts and feelings to animals," Blumberg says. "It is important, however, not to allow these anthropomorphic tendencies to interfere with our actually figuring out why animals do what they do."