Objective Further understanding of memory development in newborn infants is important because brain structures critical for memory are vulnerable to perinatal injury. Although newborns can recognize their mothers' voices, there is a high degree of prenatal and postnatal experience, and it is not clear whether lesser degrees of experience will result in memory formation. Our purpose was to further evaluate the role of experience in neonatal auditory recognition memory by comparing how newborns respond to the mother's voice (high degree of experience) or the father's voice (less experience) versus a stranger's voice using event-related potentials (ERPs), a technique commonly used in cognitive neuroscience.
Methods Subjects (N = 30) were healthy, term newborns ≤ 4 days of age. ERPs were recorded from 16 standard scalp electrodes during active sleep while listening to recordings of the word “baby” in the mother's voice alternating with a female stranger's voice or father's voice alternating with a male stranger's voice.
Results Of the 15 mothers, 80% spoke specifically to the fetus in utero on a daily basis and all spoke frequently to the infant after birth. Of the 15 fathers, 66% reported talking specifically to the fetus daily (33%) or weekly (33%). Postnatally, 73% of the fathers spent 12 to 24 hours per day rooming-in and 93% spoke frequently to the baby. Infants' ERPs demonstrated recognition of both mothers' and fathers' voices, evidenced by increased negativity to the stranger's voice from 400 to 1200 msec over the midline frontal electrode (Fz) (mean amplitude for parent's voice: 2.2 ± 1.8 μv; stranger's voice: −2.0 ± 1.3 μv; p = .0216), with similar amplitudes for fathers' and mothers' voices. There was a significant difference between male and female voices over the right hemisphere, most notable over the posterior right temporal area (T6) from 1,200 to 2,000 msec, with amplitudes for male voices (father and stranger, 1.4 ± 1.4 μv) significantly greater than those elicited by female voices (mother and stranger, −2.0 ± 1.1 μv; p = .045).
Conclusion Although pre- and postnatal exposure to the fathers' voices was less than to the mothers' voices, the exposures to the fathers' voices reported in this study were sufficient to elicit ERP patterns associated with recognition memory. Differences in responses between male and female voices over the right hemisphere may indicate the development of specialization within the auditory cortex. Further investigation to quantify the amount of experience required for auditory encoding will be useful in developing assessments for infants at risk of perinatal brain injury.
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