Saito et al.1 showed, by means of a two channel NIRS, a differential response of the neonatal brain to maternal Infant Directed Speech (IDS), in comparison to Adult Directed Speech (ADS). Their study is very interesting. They hypothesize that a newborn is able to distinguish between different emotional communications in the first days of life. These results reignite the discussion on early predisposition for newborns’ recognition of their mothers, and on how early relational skills in newborns correlate with fetal learning abilities in the intrauterine environment.

There seem to be a few points that deserve further clarification. First, the operative definitions (or the acoustic characteristics that differentiated mothers’ voices) of IDS and ADS are not clear. IDS has been characterized by parameters such as emphasized pitch, longer breaks, increase in fundamental frequency, stressing of accented syllables and slower rhythm2. In fact, most of these shortfalls are mentioned in a previous paper by the same authors (Saito et al. 3). In our opinion, an unequivocal control of acoustic parameters present in verbal stimulation heard by newborns is highly desirable.

Second, the depiction of the possible roles played by frontal and prefrontal cortex appears to be incompletely explained, especially considering their functional subdivisions and their complex and reciprocal antagonistic actions4. Furthermore, the maturational process of these cortical areas in the neonate may deserve a more extensive discussion.

Third: the statistical analyses performed do not demonstrate any significant effect and do not seem to support the authors’main claim (i.e., the right cerebral hemisphere is more activated than the left in IDS vs. ADS). There was only a trend toward a significant difference in the cortical activation evoked by IDS vs ADS (p = .07). This data was obtained in a post-hoc test done without interaction between factors, and standard deviations appeared to be excessively wide. Although this is a fascinating research, we would obviously agree with statements such as “IDS functions as a positive stimulation for the emotional development of infants” but at the same time consider rather premature on the scarce data available, and even more so about the suggested functional lateralization for IDS (emotional) processing in the neonatal brain. A multichannel NIRS system, such as the Optical Topography, is needed to detect the distribution of cortical activation. Improved spatial resolution is required in mapping cerebral regions involved in complex functions such as emotional expression.

References

1 Saito Y, Aoyama S, Kondo T, et al. Frontal cerebral blood flow change associated with infant-directed speech. Arch Dis Child Fetal Neonatal Ed 2007; 92: 113-6.

2 Fernald A, Kuhl PK. Acoustic determinants of infant preference for motherese speech. Inf Behav Dev 1987; 10: 864-81.

3 Saito Y, Kondo T, Aoyama S, et al. The function of the frontal lobe in neonates for response to a prosodic voice. Early Hum Dev 2007; 83: 225- 230.

4 Goldman-Rakic PS, Cools AR, Srivastava K. The Prefrontal Landscape: Implications of Functional Architecture for Understanding Human Mentation and the Central Executive Philos Trans R Soc Lond B Biol Sci 1996; 351 (1346): 1445-1453.