Feasibility of event-related potential (ERP) biomarker use to study effects of mother's voice exposure on speech sound differentiation of preterm infants

Investigation of mothers' elicited infant-directed speech and singing for preterm infants

BACKGROUND

Mother's voice is a salient auditory stimulus commonly experienced during early development; after birth, characteristic acoustic modulations of mothers' infant-directed speech (IDSpeech) and singing (IDSinging) contribute to neurodevelopment. For preterm infants, early separation leads to decreased exposure to mother's voice; the impact on maternal ability to produce IDSpeech/IDSinging and infant perception of mother's voice is unknown.

METHODS

Fifty mother/preterm-infant dyads were enrolled in this prospective cohort study. Forty-four mothers recorded Twinkle, Twinkle Little Star in coached adult-directed speech (ADSpeech), IDSpeech, and IDSinging. Between 34.0-36.9w CGA, infants underwent high-density EEG during exposure to their mother's voice recordings. Acoustic features of mothers' voice and infant cortical response were analyzed and correlated.

RESULTS

Acoustic features of recorded maternal ADSpeech, IDSpeech, and IDSinging were significantly different. In 33 infants with EEG, mean fundamental frequency and speech production rate (SPR) variability correlated with infant responses to ADSpeech; SPR and SPR variability correlated with IDSpeech; SPR correlated with IDSinging. Correlations were found at differing scalp locations for speech versus singing.

CONCLUSION

Mothers of hospitalized preterm infants differentially modulate their voice during coached recorded language; features can then be differentiated by their preterm infants thus presenting opportunities for targeted interventions when parents cannot be present.

IMPACT

Mothers of preterm infants can record their voice with acoustically quantifiable characteristics of infant-directed singing and speech, even when not at their infant's bedside. Recorded adult- and infant-directed speech stimuli are differentially processed in the brains of hospitalized preterm infants. The ability for mothers to create acoustically-distinct infant-directed speech in the absence of their infant may be driven by coaching to achieve an approximated sense of connection with their infant.

Eligible Infants Included in Neonatal Clinical Trials and Reasons for Noninclusion: A Systematic Review

Importance

Results of clinical trials can only represent included participants, and many neonatal trials fail due to insufficient participation. Infants not included in research may differ from those included in meaningful ways, biasing the sample and limiting the generalizability of findings.

Objective

To describe the proportion of eligible infants included in neonatal clinical trials and the reasons for noninclusion.

Evidence Review

A systematic search of Cochrane CENTRAL was performed by retrieving articles meeting the following inclusion criteria: full-length, peer-reviewed articles describing clinical trial results in at least 20 human infants from US neonatal intensive care units, published in English, and added to Cochrane CENTRAL between 2017 and 2022. Retrieved articles were screened for inclusion by 2 independent researchers.

Findings

In total 120 articles met inclusion criteria and 91 of these (75.8%) reported the number of infants eligible for participation, which totaled 26 854 in aggregate. Drawing from these, an aggregate of 11 924 eligible infants (44.4%) were included in reported results. Among all eligible infants, most reasons for noninclusion in results were classified as modifiable or potentially modifiable by the research team. Parents declining to participate (8004 infants [29.8%]) or never being approached (2507 infants [9.3%]) were the 2 predominant reasons for noninclusion. Other modifiable reasons included factors related to study logistics, such as failure to appropriately collect data on enrolled infants (859 of 26 854 infants [3.2%]) and other reasons (1907 of 26 854 infants [7.1%]), such as loss to follow-up or eligible participants that were unaccounted for. Nonmodifiable reasons, including clinical change or death, accounted for a small proportion of eligible infants who were not included (858 of 26 854 infants [3.2%]).

Conclusions and Relevance

This systematic review of reporting on eligible infants included and not included in neonatal clinical trials highlights the need for improved documentation on the flow of eligible infants through neonatal clinical trials and may also inform recruitment expectations for trialists designing future protocols. Improved adherence to standardized reporting may clarify which potential participants are being missed, improving understanding of the generalizability of research findings. Furthermore, these findings suggest that future work to understand why parents decline to participate in neonatal research trials and why some are never approached about research may help increase overall participation.

Sensitivity to vocal emotions emerges in newborns at 37 weeks gestational age

Emotional responsiveness in neonates, particularly their ability to discern vocal emotions, plays an evolutionarily adaptive role in human communication and adaptive behaviors. The developmental trajectory of emotional sensitivity in neonates is crucial for understanding the foundations of early social-emotional functioning. However, the precise onset of this sensitivity and its relationship with gestational age (GA) remain subjects of investigation. In a study involving 120 healthy neonates categorized into six groups based on their GA (ranging from 35 and 40 weeks), we explored their emotional responses to vocal stimuli. These stimuli encompassed disyllables with happy and neutral prosodies, alongside acoustically matched nonvocal control sounds. The assessments occurred during natural sleep states using the odd-ball paradigm and event-related potentials. The results reveal a distinct developmental change at 37 weeks GA, marking the point at which neonates exhibit heightened perceptual acuity for emotional vocal expressions. This newfound ability is substantiated by the presence of the mismatch response, akin to an initial form of adult mismatch negativity, elicited in response to positive emotional vocal prosody. Notably, this perceptual shift's specificity becomes evident when no such discrimination is observed in acoustically matched control sounds. Neonates born before 37 weeks GA do not display this level of discrimination ability. This developmental change has important implications for our understanding of early social-emotional development, highlighting the role of gestational age in shaping early perceptual abilities. Moreover, while these findings introduce the potential for a valuable screening tool for conditions like autism, characterized by atypical social-emotional functions, it is important to note that the current data are not yet robust enough to fully support this application. This study makes a substantial contribution to the broader field of developmental neuroscience and holds promise for future research on early intervention in neurodevelopmental disorders.

Longstanding Auditory Sensory and Semantic Differences in Preterm Born Children

More than 10% of births are preterm, and the long-term consequences on sensory and semantic processing of non-linguistic information remain poorly understood. 17 very preterm-born children (born at < 33 weeks gestational age) and 15 full-term controls were tested at 10 years old with an auditory object recognition task, while 64-channel auditory evoked potentials (AEPs) were recorded. Sounds consisted of living (animal and human vocalizations) and manmade objects (e.g. household objects, instruments, and tools). Despite similar recognition behavior, AEPs strikingly differed between full-term and preterm children. Starting at 50ms post-stimulus onset, AEPs from preterm children differed topographically from their full-term counterparts. Over the 108-224ms post-stimulus period, full-term children showed stronger AEPs in response to living objects, whereas preterm born children showed the reverse pattern; i.e. stronger AEPs in response to manmade objects. Differential brain activity between semantic categories could reliably classify children according to their preterm status. Moreover, this opposing pattern of differential responses to semantic categories of sounds was also observed in source estimations within a network of occipital, temporal and frontal regions. This study highlights how early life experience in terms of preterm birth shapes sensory and object processing later on in life.

Race and Ethnicity of Infants Enrolled in Neonatal Clinical Trials: A Systematic Review

Importance

Representativeness of populations within neonatal clinical trials is crucial to moving the field forward. Although racial and ethnic disparities in research inclusion are well documented in other fields, they are poorly described within neonatology.

Objective

To describe the race and ethnicity of infants included in a sample of recent US neonatal clinical trials and the variability in this reporting.

Evidence Review

A systematic search of US neonatal clinical trials entered into Cochrane CENTRAL 2017 to 2021 was conducted. Two individuals performed inclusion determination, data extraction, and quality assessment independently with discrepancies adjudicated by consensus.

Findings

Of 120 studies with 14 479 participants that met the inclusion criteria, 75 (62.5%) included any participant race or ethnicity data. In the studies that reported race and ethnicity, the median (IQR) percentage of participants of each background were 0% (0%-1%) Asian, 26% (9%-42%) Black, 3% (0%-12%) Hispanic, 0% (0%-0%) Indigenous (eg, Alaska Native, American Indian, and Native Hawaiian), 0% (0%-0%) multiple races, 57% (30%-68%) White, and 7% (1%-21%) other race or ethnicity. Asian, Black, Hispanic, and Indigenous participants were underrepresented, while White participants were overrepresented compared with a reference sample of the US clinical neonatal intensive care unit (NICU) population from the Vermont Oxford Network. Many participants were labeled as other race or ethnicity without adequate description. There was substantial variability in terms and methods of reporting race and ethnicity data. Geographic representation was heavily skewed toward the Northeast, with nearly one-quarter of states unrepresented.

Conclusions and Relevance

These findings suggest that neonatal research may perpetuate inequities by underrepresenting Asian, Black, Hispanic, and Indigenous neonates in clinical trials. Studies varied in documentation of race and ethnicity, and there was regional variation in the sites included. Based on these findings, funders and clinical trialists are advised to consider a 3-point targeted approach to address these issues: prioritize identifying ways to increase diversity in neonatal clinical trial participation, agree on a standardized method to report race and ethnicity among neonatal clinical trial participants, and prioritize the inclusion of participants from all regions of the US in neonatal clinical trials.

Behavioral and neural measures of infant responsivity increase with maternal multisensory input in non-irritable infants

INTRODUCTION

Parents often use sensory stimulation during early-life interactions with infants. These interactions, including gazing, rocking, or singing, scaffold child development. Previous studies have examined infant neural processing during highly controlled sensory stimulus presentation paradigms.

OBJECTIVE

In this study, we investigated infant behavioral and neural responsiveness during a mother-child social interaction during which the mother provided infant stimulation with a progressive increase in the number of sensory modalities.

METHODS

We prospectively collected and analyzed video-coded behavioral interactions and electroencephalogram (EEG) frontal asymmetry (FAS) from infants (n = 60) at 2-4 months born at ≥ 34 weeks gestation. As the number of sensory modalities progressively increased during the interaction, infant behaviors of emotional connection in facial expressiveness, sensitivity to mother, and vocal communication increased significantly. Conversely, infant FAS for the entire cohort did not change significantly. However, when we accounted for infant irritability, both video-coded behaviors and EEG FAS markers of infant responsiveness increased across the interaction in the non-irritable infants. The non-irritable infants (49%) demonstrated positive FAS, indicating readiness to engage with, rather than to withdraw from, multisensory but not unisensory interactions with their mothers.

RESULTS

These results suggest that multisensory input from mothers is associated with greater infant neural approach state and highlight the importance of infant behavioral state during neural measures of infant responsiveness.

Contingent Mother's Voice Intervention Targeting Feeding in Hospitalized Infants with Critical Congenital Heart Defects

Infants with critical congenital heart defects (CCHD) are at high risk for feeding challenges and neurodevelopmental delays; however, few interventions promoting the neurodevelopmental progression of feeding have been studied with this population. Contingent mother's voice has been successfully used as positive reinforcement for non-nutritive suck (NNS) in studies with preterm infants, leading to improved weight gain and more rapid cessation of tube feedings; however, this type of intervention has not been studied in infants with CCHD. This study aimed to determine whether an NNS-training protocol using the mother's voice as positive reinforcement and validated in preterm infants could improve oral feeding outcomes in hospitalized infants with CCHD undergoing cardiac surgical procedures. Infants were randomized to receive the contingent mother's voice intervention before or after cardiac surgery, with a control comparison group receiving passive exposure to the mother's voice after surgery. There were no significant differences in discharge weight, PO intake, length of stay, time to full feeds, or feeding status at 1-month post-discharge between infants who received contingent mother's voice compared to those who did not. There were significant differences in PO intake and time to full feeds following surgery based on infants' pre-enrollment PO status and severity of illness. At 1-month post-discharge, parents of infants in the intervention group expressed a higher rate of positive feelings and fewer concerns regarding their infant's feeding compared to parents of infants in the control group. While the current protocol of 5 sessions was not associated with improved feeding outcomes in infants with CCHD, it empowered parents to contribute to their infant's care and demonstrated the feasibility of using the mother's voice as positive reinforcement for infants with CCHD. Further study of timing, intensity, and duration of interventions leveraging the mother's voice in this population is needed. ClinicalTrials.gov Identifier: NCT03035552.

Musical and vocal interventions to improve neurodevelopmental outcomes for preterm infants

BACKGROUND

Preterm birth interferes with brain maturation, and subsequent clinical events and interventions may have additional deleterious effects. Music as therapy is offered increasingly in neonatal intensive care units aiming to improve health outcomes and quality of life for both preterm infants and the well-being of their parents. Systematic reviews of mixed methodological quality have demonstrated ambiguous results for the efficacy of various types of auditory stimulation of preterm infants. A more comprehensive and rigorous systematic review is needed to address controversies arising from apparently conflicting studies and reviews.

OBJECTIVES

We assessed the overall efficacy of music and vocal interventions for physiological and neurodevelopmental outcomes in preterm infants (< 37 weeks' gestation) compared to standard care. In addition, we aimed to determine specific effects of various interventions for physiological, anthropometric, social-emotional, neurodevelopmental short- and long-term outcomes in the infants, parental well-being, and bonding.

SEARCH METHODS

We searched Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, CINAHL, PsycINFO, Web of Science, RILM Abstracts, and ERIC in November 2021; and Proquest Dissertations in February 2019. We searched the reference lists of related systematic reviews, and of studies selected for inclusion and clinical trial registries.

SELECTION CRITERIA

We included parallel, and cluster-randomised controlled trials with preterm infants < 37 weeks` gestation during hospitalisation, and parents when they were involved in the intervention. Interventions were any music or vocal stimulation provided live or via a recording by a music therapist, a parent, or a healthcare professional compared to standard care. The intervention duration was greater than five minutes and needed to occur more than three times.

DATA COLLECTION AND ANALYSIS

Three review authors independently extracted data. We analysed the treatment effects of the individual trials using RevMan Web using a fixed-effects model to combine the data. Where possible, we presented results in meta-analyses using mean differences with 95% CI. We performed heterogeneity tests. When the I2 statistic was higher than 50%, we assessed the source of the heterogeneity by sensitivity and subgroup analyses. We used GRADE to assess the certainty of the evidence.

MAIN RESULTS

We included 25 trials recruiting 1532 infants and 691 parents (21 parallel-group RCTs, four cross-over RCTs). The infants gestational age at birth varied from 23 to 36 weeks, taking place in NICUs (level 1 to 3) around the world. Within the trials, the intervention varied widely in type, delivery, frequency, and duration. Music and voice were mainly characterised by calm, soft, musical parameters in lullaby style, often integrating the sung mother's voice live or recorded, defined as music therapy or music medicine. The general risk of bias in the included studies varied from low to high risk of bias. Music and vocal interventions compared to standard care Music/vocal interventions do not increase oxygen saturation in the infants during the intervention (mean difference (MD) 0.13, 95% CI -0.33 to 0.59; P = 0.59; 958 infants, 10 studies; high-certainty evidence). Music and voice probably do not increase oxygen saturation post-intervention either (MD 0.63, 95% CI -0.01 to 1.26; P = 0.05; 800 infants, 7 studies; moderate-certainty evidence). The intervention may not increase infant development (Bayley Scales of Infant and Toddler Development (BSID)) with the cognitive composition score (MD 0.35, 95% CI -4.85 to 5.55; P = 0.90; 69 infants, 2 studies; low-certainty evidence); the motor composition score (MD -0.17, 95% CI -5.45 to 5.11; P = 0.95; 69 infants, 2 studies; low-certainty evidence); and the language composition score (MD 0.38, 95% CI -5.45 to 6.21; P = 0.90; 69 infants, 2 studies; low-certainty evidence). Music therapy may not reduce parental state-trait anxiety (MD -1.12, 95% CI -3.20 to 0.96; P = 0.29; 97 parents, 4 studies; low-certainty evidence). The intervention probably does not reduce respiratory rate during the intervention (MD 0.42, 95% CI -1.05 to 1.90; P = 0.57; 750 infants; 7 studies; moderate-certainty evidence) and post-intervention (MD 0.51, 95% CI -1.57 to 2.58; P = 0.63; 636 infants, 5 studies; moderate-certainty evidence). However, music/vocal interventions probably reduce heart rates in preterm infants during the intervention (MD -1.38, 95% CI -2.63 to -0.12; P = 0.03; 1014 infants; 11 studies; moderate-certainty evidence). This beneficial effect was even stronger after the intervention. Music/vocal interventions reduce heart rate post-intervention (MD -3.80, 95% CI -5.05 to -2.55; P < 0.00001; 903 infants, 9 studies; high-certainty evidence) with wide CIs ranging from medium to large beneficial effects. Music therapy may not reduce postnatal depression (MD 0.50, 95% CI -1.80 to 2.81; P = 0.67; 67 participants; 2 studies; low-certainty evidence). The evidence is very uncertain about the effect of music therapy on parental state anxiety (MD -0.15, 95% CI -2.72 to 2.41; P = 0.91; 87 parents, 3 studies; very low-certainty evidence). We are uncertain about any further effects regarding all other secondary short- and long-term outcomes on the infants, parental well-being, and bonding/attachment. Two studies evaluated adverse effects as an explicit outcome of interest and reported no adverse effects from music and voice.

AUTHORS' CONCLUSIONS

Music/vocal interventions do not increase oxygen saturation during and probably not after the intervention compared to standard care. The evidence suggests that music and voice do not increase infant development (BSID) or reduce parental state-trait anxiety. The intervention probably does not reduce respiratory rate in preterm infants. However, music/vocal interventions probably reduce heart rates in preterm infants during the intervention, and this beneficial effect is even stronger after the intervention, demonstrating that music/vocal interventions reduce heart rates in preterm infants post-intervention. We found no reports of adverse effects from music and voice. Due to low-certainty evidence for all other outcomes, we could not draw any further conclusions regarding overall efficacy nor the possible impact of different intervention types, frequencies, or durations. Further research with more power, fewer risks of bias, and more sensitive and clinically relevant outcomes are needed.

Prenatal daily musical exposure is associated with enhanced neural representation of speech fundamental frequency: Evidence from neonatal frequency-following responses

Fetal hearing experiences shape the linguistic and musical preferences of neonates. From the very first moment after birth, newborns prefer their native language, recognize their mother's voice, and show a greater responsiveness to lullabies presented during pregnancy. Yet, the neural underpinnings of this experience inducing plasticity have remained elusive. Here we recorded the frequency-following response (FFR), an auditory evoked potential elicited to periodic complex sounds, to show that prenatal music exposure is associated to enhanced neural encoding of speech stimuli periodicity, which relates to the perceptual experience of pitch. FFRs were recorded in a sample of 60 healthy neonates born at term and aged 12-72 hours. The sample was divided into two groups according to their prenatal musical exposure (29 daily musically exposed; 31 not-daily musically exposed). Prenatal exposure was assessed retrospectively by a questionnaire in which mothers reported how often they sang or listened to music through loudspeakers during the last trimester of pregnancy. The FFR was recorded to either a /da/ or an /oa/ speech-syllable stimulus. Analyses were centered on stimuli sections of identical duration (113 ms) and fundamental frequency (F0  = 113 Hz). Neural encoding of stimuli periodicity was quantified as the FFR spectral amplitude at the stimulus F0 . Data revealed that newborns exposed daily to music exhibit larger spectral amplitudes at F0 as compared to not-daily musically-exposed newborns, regardless of the eliciting stimulus. Our results suggest that prenatal music exposure facilitates the tuning to human speech fundamental frequency, which may support early language processing and acquisition. RESEARCH HIGHLIGHTS: Frequency-following responses to speech were collected from a sample of neonates prenatally exposed to music daily and compared to neonates not-daily exposed to music. Neonates who experienced daily prenatal music exposure exhibit enhanced frequency-following responses to the periodicity of speech sounds. Prenatal music exposure is associated with a fine-tuned encoding of human speech fundamental frequency, which may facilitate early language processing and acquisition.

Randomized Trial to Increase Speech Sound Differentiation in Infants Born Preterm

OBJECTIVE

To test whether infant-directed foreign language active learning would specifically increase speech sound differentiation to the intervention language while not decreasing differentiation in response to English.

STUDY DESIGN

Pilot randomized controlled trial of stable infants born preterm in the newborn intensive care unit with normal auditory brainstem responses, whose parents spoke only English and had no musical training or familial hearing abnormality. Assignment was to 1 of 3 groups: passive exposure to English infant-directed lullabies and readings (English-enrichment, control group) and contingent exposure by active sucking on a sensor-equipped pacifier to either infant-directed French lullabies and readings (English environment, French-contingent learning group) or infant-directed Mandarin lullabies and readings (English environment, Chinese-contingent learning group). The main outcome measures were preintervention and postintervention event-related potentials (ERPs) in response to standardized speech syllables in each language.

RESULTS

Forty-one subjects completed the study, including 15 in the English-enrichment control group and 13 each in the French-contingent and Chinese-contingent groups. The median gestational age at birth was 34 weeks (IQR, 8.75 weeks); postmenstrual age at intervention ranged from 36 to 46 weeks and was similar across the 3 groups. Postintervention mean ERP amplitude to pairs of English speech sounds did not differ across the 3 groups; however, ERP amplitude in French sound differentiation was greater in the French-contingent group than in the Chinese-contingent or English-enrichment groups, and ERP amplitude greater in Chinese sound differentiation was greater in the Chinese-contingent group compared with the other 2 groups.

CONCLUSION

Contingent infant-directed foreign language exposure increased speech sound differentiation specific to the intervention language and did not decrease differentiation in response to English.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT03232931.

Fetal Middle Cerebral Artery Pulsatility Index in No-Risk Pregnancies: Effects of Auditory Stimulation and Pregnancy Order

Pulsatility index (PI) values in a fetal middle cerebral artery (MCA) were compared in no-risk pregnancies to examine the differences related to auditory stimulation test and pregnancy order. The study included 196 women with no-risk pregnancies selected from the database of more than 1000 pregnant women divided into two groups. Group 1 consisted of 98 nulliparous women (C1 = 98) and Group 2 consisted of 98 parous women (C2 = 98). All pregnant women were of comparable age and fetal gestational age (GA) when MCA-PI values were recorded. Measurements of PI values in fetal MCA were obtained before and immediately after the application of fetal auditory stimulation test. The MCA-PI measuring was conducted in the period between the 36th and the 41st week of GA. The results showed that PI baseline values and PI values after defined auditory stimulation were significantly different when measured in nulliparous women compared to parous women (p = 0.001; p = 0.003, respectively), while no group differences were observed in relative PI value changes due to auditory stimulation. These findings suggest that hemodynamic changes in fetal MCA caused by defined auditory stimulation measured by PI value changes may be valuable in the assessment of fetal auditory perception functionality and its development.

Neuroprocessing Mechanisms of Music during Fetal and Neonatal Development: A Role in Neuroplasticity and Neurodevelopment

The primary aim of this viewpoint article is to examine recent literature on fetal and neonatal processing of music. In particular, we examine the behavioral, neurophysiological, and neuroimaging literature describing fetal and neonatal music perception and processing to the first days of term equivalent life. Secondly, in light of the recent systematic reviews published on this topic, we discuss the impact of music interventions on the potential neuroplasticity pathways through which the early exposure to music, live or recorded, may impact the fetal, preterm, and full-term infant brain. We conclude with recommendations for music stimuli selection and its role within the framework of early socioemotional development and environmental enrichment.