Tabula Rasa? A History of Fetal Learning and Neonatal Perception.

Abstract

Background: Sensory capacities of the fetus and newborn are still incompletely known. This paper delineates the history of understanding and evidence.

Summary: In the 2nd century, Galen propagated the tabula rasa theory comparing newborns to a blank writing tablet, without senses of sight, hearing, taste, or smell. Somatosensory: once the microscope was available, tactile receptors were identified in mid-17th century. But the tabula rasa theory persisted, and physicians maintained until the 1980s that neonates feel no pain. Auditory: the inner ear's development begins at 10 weeks of gestation at the cochlear basis and ends at its apex at 24 weeks. Researchers believed still into the 19th century that the fetus lacked auditory sensitivity. The uterus is not a quiet place, as the fetus hears uterine vessels, maternal voice, peristalsis, diaphragmatic movement, and heartbeat. In 1980, DeCasper proved that newborns preferred hearing their mothers' voice when compared to that of another mother. The evidence is weaker for sounds originating outside the maternal body. Despite little in-utero stimulation, the newborn's visual apparatus functions from birth. Infants enter the world with innate perceptual knowledge of the human face. Olfactory: human infants are attracted by the smell of their mother's breast. It took 1500 years to discard the tabula rasa theory and to grant the newborn full personhood in the 20th century.

Key messages: Fetal sensory organs are developed by mid-gestation. Neonates know their mother's voice and smell, which encourages maternal contact, prudent disinfectant use, and reduced noise in the nursery.