The remembered associations surrounding an infant’s first meal — smells, sounds and taste — are so deeply embedded and powerful they can last a lifetime.
For more than 30 years Norman Spear and his colleagues have been attempting to figure out how learning and memory develop for infants and whether early memories of alcohol exposure might contribute to later abuse of alcohol.
The work by Spear, distinguished professor of psychology; colleagues Evgeniy Petrov and Elena Varlinskaya, both physicians and research professors at BU, and Juan Carlos Molina of the Institute Ferreyra in Argentina, may help unlock the secrets of alcohol dependency. The research has been funded for more than 30 years by the National Institute on Alcohol Abuse and Alcoholism and the National Institute of Mental Health. Current NIH grants to Spear exceed $2.5 million.
Working with rat pups, some only hours old, Spear and his colleagues have discovered that even at its first meal, the newborn’s behavior can be influenced by olfactory and taste cues. The next question is how well the rats remember those lessons as they mature.
Spear says that Sigmund Freud had it wrong when he postulated that adults could not remember things learned as infants — he termed it “infantile amnesia” — because those events were associated with socially undesirable events.
“Freud was wrong about it,” Spear says. “It was not a social problem. All altricial mammals (those born with very immature brains) forget the events of their infancy more completely than later events, and with animals it is unlikely that social standards are involved.”
However, Spear is finding that the memory for things learned in conjunction with the infant’s first meal may not be forgotten as rapidly as other events of infancy. “Things learned then seem to be special,” he says.
Spear and colleagues have tested their theory on hours-old rats that were delivered by cesarean section. The rat pups were given a drop or two of milk, preceded by a sniff of lemon oil. “That gives the odor a lot of power,” says Spear.
Later, when presented with a dry nipple after a lemon-scented cotton swab, the rats suckled for about 80 percent of a 10-minute period. Rat pups in control groups not exposed to the lemon-milk pairing suckled only about 20 percent of the time.
Spear’s team repeated the lemon-milk pairing with another group of rat pups, but this time allowed a minute to lapse between the presentation of the lemon scent and the milk. In spite of the time lapse — which in older infants would not result in a conditioned pairing — the rat pups became conditioned to suckle in response to the lemon scent.
Spear concludes that the conditioning in the newborn might be especially robust for at least two reasons. First, in natural circumstances an odor and a nipple are the cues that direct rat pups to their first meal so newborn rats might be predisposed to learn the odor-nipple association. Or, Spear says, it could be that the pups are blank sensory slates — aside from their fetal experience — and the first significant sensory information they encounter,the lemon odor and the milk taste, forms a special bond due to its primacy.
In either event, the experiment demonstrates that even primitive events, such as suckling at a newborn’s first meal, are learned and offer clues as to how the mechanics of memory and reinforcement operate.
Spear is working on a concurrent series of experiments with rat pups and ethanol, the form of alcohol that is the basic ingredient in commercial alcoholic beverages.
“What we’re working on now is the question, ‘Is alcohol rewarding to infant rats and fetuses?’ ” In particular, he is asking how early exposure to alcohol, both prenatally and postnatally, affects later responsiveness to alcohol, including alcohol abuse.
The first challenge in the postnatal-exposure experiments is to get the rat pups to drink alcohol. Spear notes that older rats don’t like alcohol. (“You have to trick them into it,” he said,) Then he charts the physiological and conditioned learning effects under various conditions when alcohol is the reward for learning.
“What we’re finding is that, within the first two weeks after birth, infants readily drink more alcohol,” he says. “They consume two to three times more alcohol than water. What we’re able to show is that alcohol is rewarding, and at some concentrations it’s as rewarding as milk.”
The second form of exposure that rat pups get to alcohol is via the mother during gestation or nursing. The alcohol gets into the amniotic fluid and the fetus is exposed directly to both the flavor of alcohol and alcohol’s pharmacological “buzz.” Nursing rat pups may also be exposed to alcohol-contaminated milk.
While Spear’s work is with rats, the implications extend to humans. For instance, the research involving rat fetuses that absorb alcohol via an intoxicated mother may have implications for understanding Fetal Alcohol Syndrome and the less extreme Fetal Alcohol Effect, two conditions that affect children born to alcoholic mothers. Spear notes that Fetal Alcohol Syndrome was only definitively identified and labeled as such less than 30 years ago, so research into the underlying issues of alcohol and fetus-infant development is still in its infancy.
Scientists have judged that more cases of mental retardation are due to prenatal exposure to alcohol than to any other single cause. Fetal Alcohol Syndrome generally affects one of every 1,000 newborns and two per 1,000 births in some socioeconomic groups. Fetal Alcohol Effect, which has milder symptoms, is far more prevalent. Because of structural and neurochemical changes in the brain caused by the prenatal ingestion of alcohol, these children have learning and behavioral difficulties that hamper them their entire lives. In many instances these children also have a high predisposition toward alcoholism in later life.
Along with the basic research regarding alcohol, Spear is advancing science’s understanding of the role of prenatal learning, the importance of senses in learning and the link between the senses, memory and learning.
Spear, who came to Binghamton in 1974, received a bachelor’s degree in mathematics and another in psychology from Bowling Green State University. He earned his master’s and doctoral degrees in experimental psychology from Northwestern University. Prior to teaching at Binghamton, Spear served on the faculty of Rutgers University, one of the nation’s premier schools for alcohol studies.
“What the newborn rat can tell us about the human condition is very, very important,” says Spear.