Important implications for infants who must change formulas or need to ingest medicine
WASHINGTON - Learning when to suckle is one of the most important life skills newborn mammals have to acquire in order to survive. New research published in the June issue of Behavioral Neuroscience, published by the American Psychological Association (APA), has shown a strong link between odor and suckling and that there is a powerful learning mechanism behind a newborn's suckling behavior.
Psychologist Norman E. Spear, Ph.D., and colleagues Evgeniy Petrov, M.D., Ph.D., Lena Varlinskaya, M.D., Ph.D., and Sarah Cheslock at Binghamton University of the State University of New York, found that newborn rat pups who were exposed to the pairing of lemon odor and milk - even just once - suckled on a surrogate nipple 80 percent of a ten minute testing period while pups in three control groups suckled for only 20 percent of the test period. This finding shows that learning as related to suckling behavior is so strong in new born rats that they can be conditioned to suckle on an empty surrogate nipple if the surrogate is associated with a novel scent - a scent the rats were previously exposed to followed by an infusion of a small amount of milk.
In addition, Spear and his research team found that they could wait as long as one minute between the presentation of the lemon scent and the milk infusion and still condition the pups to suckle in response to the lemon scent. According to Dr. Spear, this finding is particularly interesting because other research has shown that older rat pups normally don't tolerate this length of trace interval during conditioning experiments. That is, unless the two stimuli are presented closer together, the pup fails to associate the two.
Dr. Spear hypothesizes that the pups pair the lemon scent and milk even with the one minute intervals because milk is an important source of nutrition for newborns and odor is a significant signal for it in natural circumstances, immediately after birth and later. Or, a second possible explanation - that the pups are so young (just hours old) that there are very few previous sensory learning experiences for the scent/milk pairing to compete with.
"This is an incredibility strong finding," says Spear. "It shows that there is a powerful learning mechanism behind suckling and it may help illuminate basic learning, memory and reinforcement mechanisms in the brain."
This finding joins a growing body of research that shows that infant suckling can be manipulated through conditioning. For example, Dr. Warren G. Hall of Duke University studies the link between odor and suckling in human babies. One of his research projects is building a conditioning paradigm to help human infants transition from one type of formula to another as often has to be done for medical reasons.
In other work Dr. Spear and his team have found that alcohol reinforces suckling in newborns just as strongly as milk - another surprising finding because adult rats usually won't drink alcohol. Dr. Spear believes that because brain development in rats is simpler than in humans and therefore easier to study, this research may lead to a better model for understanding the reinforcement mechanisms of alcohol and therefore the underpinnings of alcohol dependency.
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