Hemispheric asymmetry of late auditory evoked response induced by pitch changes in infants: influence of sleep stages

Early maturation of neural auditory novelty detection - Typical development with no major effects of dyslexia risk or music intervention

OBJECTIVE

To determine the early development of novelty detection and the effect of familial dyslexia risk and infant music intervention on this development.

METHODS

In the longitudinal DyslexiaBaby study, we investigated the maturation of novelty-P3 and late-discriminative negativity (LDN) event-related potentials to novel sounds at birth (N = 177) and at the ages of 6 (N = 83) and 28 months (N = 131).

RESULTS

Novelty-P3 was elicited at all ages, whereas LDN was elicited at 6 and 28 months. Novelty-P3 amplitude was largest at 6 months, and its latency decreased with age. LDN amplitude decreased and latency increased between 6 to 28 months. Dyslexia risk or intervention had no effects, apart from a longer LDN latency in the high-risk than no-risk group.

CONCLUSIONS

Already neonates respond to novel environmental sounds, indicating prerequisites for detecting potentially relevant events at birth. Maturation influences neural novelty detection.

SIGNIFICANCE

Novelty detection is crucial for perceiving important events, but its early development has been scarcely studied. We found, with a large sample, that neonates detect novel events, and showed the developmental pattern of its neural signature. The results serve as a reference for studies on typical and atypical novelty-detection development in infancy when behavioral testing is challenging.

Cerebral lateralization and early speech acquisition: a developmental scenario

During the past ten years, research using Near-infrared Spectroscopy (NIRS) to study the developing brain has provided groundbreaking evidence of brain functions in infants. This paper presents a theoretically oriented review of this wealth of evidence, summarizing recent NIRS data on language processing, without neglecting other neuroimaging or behavioral studies in infancy and adulthood. We review three competing classes of hypotheses (i.e. signal-driven, domain-driven, and learning biases hypotheses) regarding the causes of hemispheric specialization for speech processing. We assess the fit between each of these hypotheses and neuroimaging evidence in speech perception and show that none of the three hypotheses can account for the entire set of observations on its own. However, we argue that they provide a good fit when combined within a developmental perspective. According to our proposed scenario, lateralization for language emerges out of the interaction between pre-existing left-right biases in generic auditory processing (signal-driven hypothesis), and a left-hemisphere predominance of particular learning mechanisms (learning-biases hypothesis). As a result of this completed developmental process, the native language is represented in the left hemisphere predominantly. The integrated scenario enables to link infant and adult data, and points to many empirical avenues that need to be explored more systematically.

Auditory processing during sleep in preterm infants: An event related potential study

Auditory processing during sleep was investigated in premature infants by auditory event related potentials (AERPs). Twenty-six premature infants (mean GA 30 week- range 25-35) admitted to a neonatal intensive care unit were studied, prior to discharge, in active and quiet sleep at a mean post-conceptional age of 35 weeks. Infant state was determined by behavioral observation according to standard criteria. An auditory odd-ball paradigm was used with frequently occurring 'standard' tones at 1000Hz and infrequent 'deviant' tones at 2000Hz. Waveforms were recorded at Fz, Cz, Pz, T3 and T4 scalp locations. Measurements were performed in 18 patients because 8 preterm infants were excluded since they had less than the required artifact-free deviant trials in each sleep state. The responses to standard tones were equally recorded in both active and quiet sleep, but auditory responses to deviant tones consisting of an increased frontal negativity in the time period from 200 to 300ms after the stimulus were recorded only in active sleep. A significant effect of electrode placement, for frontal location by sleep condition and sleep condition by 50ms time windows was shown by repeated measures analyses of variance. The significance of these findings on evoked potential methodology in preterm infants admitted to neonatal intensive care unit is discussed.

Early development of brain responses to rapidly presented auditory stimulation: a magnetoencephalographic study

BACKGROUND

The processing of rapidly presented stimuli has been shown to be a precursor for the perception of speech in infants, long before they learn to speak. However, the onset and early development of rapid temporal processing (RTP) skills is not yet well understood. The main goal of this study was to assess the development of RTP skills during the prenatal and early postnatal stages of life.

METHODOLOGY

Tone pairs were presented in two difficulties (long and short) and event-related magnetic fields were recorded using MEG. Pregnant women (22) (gestational ages between 29 and 38 weeks') participated in the fetal study and 15 returned for a neonatal follow-up study between 2 and 38 days after delivery or 38 and 44 weeks gestational age (GA).

RESULTS

In the postnatal follow-up study, a trend towards two peaks with increasing chronological and gestational age was observed in the longer tone pair. However, no such trend was evident in neonatal responses to the short tone pairs or in fetal recordings.

CONCLUSIONS

Neonates showed a gradual trend to successful processing of the longer tone pair with increasing age. By 22 days of chronological age, the infants processed this tone pair successfully, as indicated by two-peak waveforms. Therefore, the first 3 weeks of life could be critical for the development of RTP.

SIGNIFICANCE

This study is a first approach towards the assessment of early RTP development. The results provide promising indications for future studies, which might lead to an early detection of deficits in speech perception and therefore prevent further language impairments.

Maturation of the cortical auditory evoked potential in infants and young children

The aim of this study was to evaluate the maturation of the cortical auditory evoked potential (CAEP) in humans. The participants in this experiment were 10 newborns (<7 days), 19 toddlers (13-41 months), 20 children (4-6 years) and 9 adults (18-45 years). CAEPs were obtained in response to low (400 Hz) and high (3000 Hz) tones and to the word token /baed/, all presented at 60 dB HL, at a rate of 0.22 Hz. Latency and amplitude measures were made for CAEP components P1, N1, P2 and N2 as a function of participant age, stimulus type and electrode montage. CAEP component latencies were relatively stable from birth to 6 years, but adults demonstrated significantly shorter latencies compared to infants and children. Components P1 and N2 decreased in amplitude, while components N1 and P2 increased in amplitude from birth to adulthood. Words evoked significantly larger CAEPs in newborns compared to responses evoked by tones, but in other age groups the effects of stimulus type on component amplitudes and latencies were less consistent. There was evidence of immature tonotopic organisation of the generators of N1 when responses from infants and young children were compared to those of adults. The scalp distribution of components N1 and P2 was clearly different in newborns and toddlers compared to children and adults. In the younger groups, both N1 and P2 were uniformly distributed across the scalp but in children and adults these components showed more focal distributions, with evidence of response laterality increasing with maturity. The results of the present study describe, for the first time, CAEPs recorded from multiple scalp electrodes, for tones and speech stimuli, in infants and children from birth to 6 years of age. Frequency-related differences in component amplitude were apparent at all ages reflecting development of tonotopic organisation of the CAEP neural generators.

Maturation of CAEP in infants and children: A review

This paper reviews our current understanding of the development of the obligatory cortical auditory evoked potential (CAEP) components P1, N1, P2, and N2. Firstly, the adult CAEP is briefly reviewed with respect to its morphology, neural generators and stimulus-dependence. Secondly, age-related changes occurring from the newborn period through childhood and adolescence are reviewed. The focus is on the maturation of CAEP morphology, changes in the scalp topography of the various components, changes in their amplitude and latency and in their stimulus-dependence. This review identifies periods of development in which we have only limited understanding of cortical auditory processing, as revealed by evoked potentials.

Development of MEG sleep patterns and magnetic auditory evoked responses during early infancy

OBJECTIVE

To follow the development of MEG sleep patterns and auditory evoked responses (AERs) during the first six months of life.

METHODS

The subjects were 18 neonates, born at conceptional age (CA) 36-42 weeks, following uncomplicated pregnancies. During each session, several 10-min MEG recordings were acquired in the presence of auditory stimulation. The recordings were classified into three distinct MEG patterns-low amplitude irregular; high-amplitude slow; and mixed-based largely on MEG amplitude and frequency. Averaged AERs were computed for the entire recording and for each MEG pattern within the recording. The results were based on analysis of 61 recording sessions of the 10 subjects who yielded three or more sessions of usable data.

RESULTS

Developmental changes in the MEG sleep patterns were most pronounced at the earliest ages. By CA 48 weeks the patterns had progressed to a more mature form, characterized by the prevalence of delta wave sleep, absence of discontinuity, and development of spindling and higher amplitude delta rhythms. In contrast to the MEG patterns, the AERs did not change markedly during the first 8 weeks (CA 40-48 weeks) and showed a simple morphology, consisting of a prominent deflection at 250 ms (P250m) and a more diffuse one at around 750 ms (N750m). During the period CA 48-54 weeks, however, a relatively abrupt transition occurred to a more complex morphology, characterized by a double peak with peak latencies 150ms (P150m) and 350 ms (P350m). Beyond this period the AERs continued to evolve, showing biphasic complexes and the emergence of late components arising from outside the auditory cortex.

CONCLUSIONS

Over the age range of this study the MEG sleep patterns and AER developed in succession, rather than concurrently; i.e. development of the sleep patterns was most rapid during the first 8 weeks (CA 40-48 weeks) while major development of the AERs commenced after this time.

SIGNIFICANCE

This finding suggests that the brain must achieve a certain level of overall maturity, reflected in the character of the MEG sleep patterns at CA 48 weeks, before the cortex enters a phase of significant functional development, reflected in the more rapid evolution of the AER after CA 48 weeks. The results of this study affirm the efficacy of MEG for spatiotemporal characterization of neonatal brain activity.

Brain Event-Related Potentials (ERPs) Measured at Birth Predict Later Language Development in Children with and Without Familial Risk for Dyslexia

We report associations between brain event-related potentials (ERPs) measured from newborns with and without familial risk for dyslexia and these same children's later language and verbal memory skills at 2.5, 3.5, and 5 years of age. ERPs to synthetic consonant-vowel syllables (/ba/, /da/, /ga/; presented equiprobably with 3,910-7,285 msec interstimulus intervals) were recorded from 26 newborns at risk for familial dyslexia and 23 control infants participating in the Jyväskylä Longitudinal Study of Dyslexia. The correlation and regression analyses showed that the at-risk type of response pattern at birth (a slower shift in polarity from positivity to negativity in responses to /ga/ at 540-630 msec) in the right hemisphere was related to significantly poorer receptive language skills across both groups at the age of 2.5 years. The similar ERP pattern in the left hemisphere was associated with poorer verbal memory skills at the age of 5 years. These results demonstrate that ERPs of newborns may be valid predictors of later language and neurocognitive outcomes.

Neurophysiologic evaluation of early cognitive development in high-risk infants and toddlers

New knowledge of the perceptual, discriminative, and memory capabilities of very young infants has opened the door to further evaluation of these abilities in infants who have risk factors for cognitive impairments. A neurophysiologic technique that has been very useful in this regard is the recording of event-related potentials (ERPs). The event-related potential (ERP) technique is widely used by cognitive neuroscientists to study cognitive abilities such as discrimination, attention, and memory. This method has many attractive attributes for use in infants and children as it is relatively inexpensive, does not require sedation, has excellent temporal resolution, and can be used to evaluate early cognitive development in preverbal infants with limited behavioral repertories. In healthy infants and children, ERPs have been used to gain a further understanding of early cognitive development and the effect of experience on brain function. Recently, ERPs have been used to elucidate atypical memory development in infants of diabetic mothers, difficulties with perception and discrimination of speech sounds in infants at risk for dyslexia, and multiple areas of cognitive differences in extremely premature infants. Atypical findings seen in high-risk infants have correlated with later cognitive outcomes, but the sensitivity and specificity of the technique has not been studied, and thus evaluation of individual infants is not possible at this time. With further research, this technique may be very useful in identifying children with cognitive deficits during infancy. Because even young infants can be examined with ERPs, this technique is likely to be helpful in the development of focused early intervention programs used to improve cognitive function in high-risk infants and toddlers.

Electrophysiological evidence for delayed mismatch response in infants at-risk for specific language impairment

The present study investigated whether delayed auditory processing typically found in children with specific language impairment (SLI) can already be observed in the event-related potentials of 2-month-old infants. Infants with and without a family history of SLI were tested in a passive auditory oddball paradigm with CV-syllables differing in vowel duration. For the long syllable, a positive mismatch response occurred in the difference wave between deviant and standard. Its amplitude was higher in infants during quiet sleep than in awake infants, although its peak latency remained unaffected by alertness. Awake infants showed an adultlike mismatch negativity preceding the positivity. Risk for SLI was reflected in the latency of the positive mismatch response, which was delayed in infants with risk compared to infants without risk. This latency difference suggests that 2-month-old infants at risk for SLI are already affected in processing an auditory stimulus change of duration.

Maturational effects on newborn ERPs measured in the mismatch negativity paradigm

The mismatch negativity (MMN) component of event-related potentials (ERPs), a measure of passive change detection, is suggested to develop early in comparison to other ERP components, and an MMN-like response has been measured even from preterm infants. The MMN response in adults is negative in polarity at about 150-200 ms. However, the response measured in a typical MMN paradigm can also be markedly different in newborns, even opposite in polarity. This has been suggested to be related to maturational factors. To verify that suggestion, we measured ERPs of 21 newborns during quiet sleep to rarely occurring deviant tones of 1100 Hz (probability 12%) embedded among repeated standard tones of 1000 Hz in an oddball sequence. Gestational age (GA) and two cardiac measures, vagal tone (V) and heart period (HP), were used as measures of maturation. GA and HP explained between 36% and 42% of the total variance of the individual ERP peak amplitude (the largest deflection of the difference wave at a time window of 150-375 ms) at different scalp locations. In the discriminant function analyses, GA and HP as classifying variables differentiated infants in whom the peak of the difference wave had positive polarity from those with a negative polarity at an accuracy level ranging from 72% to 91%. These results demonstrate that during quiet sleep, maturational factors explain a significant portion of the ERP difference wave amplitude in terms of its polarity, indicating that the more mature the ERPs are, the more positive the amplitude. The present study suggests that maturational effects should be taken into account in ERP measurements using MMN paradigms with young infants.

Common Neural Basis for Phoneme Processing in Infants and Adults

Investigating the degree of similarity between infants' and adults' representation of speech is critical to our understanding of infants' ability to acquire language. Phoneme perception plays a crucial role in language processing, and numerous behavioral studies have demonstrated similar capacities in infants and adults, but are these subserved by the same neural substrates or networks? In this article, we review event-related potential (ERP) results obtained in infants during phoneme discrimination tasks and compare them to results from the adult literature. The striking similarities observed both in behavior and ERPs between initial and mature stages suggest a continuity in processing and neural structure. We argue that infants have access at the beginning of life to phonemic representations, which are modified without training or implicit instruction, but by the statistical distributions of speech input in order to converge to the native phonemic categories.

Maturation of mismatch negativity in typically developing infants and preschool children

OBJECTIVE

1) To determine whether an adult-like mismatch negativity (MMN) can be reliably elicited in typically developing awake infants and preschool children, and if so 2) to examine whether maturational changes exist in MMN latencyand amplitude.

DESIGN

Two experiments were designed to elicit MMN using an "oddball" paradigm. In Experiment 1, a 1000-Hz tone served as the standard stimulus and a 1200-Hz tone as the deviant. In Experiment 2, a 1000-Hz standard stimulus and a 2000-Hz deviant were presented. Infants' ages ranged from 2 to 47 and 3 to 44 mo in Experiments 1 and 2, respectively.

RESULTS

In Experiment 1, a negativity was not elicited in the majority of the infants and preschoolers tested. In Experiment 2, a negativity was reliably elicited in the infants and preschoolers across all ages. A significant negative correlation was observed between age and latency, but not for age and amplitude for this negativity. This negativity was found to decrease at a rate of 1 msec/mo. Infants younger than 12 mo of age showed a significantly larger positivity to the deviant than to the standard between 150-300 and 200-300 msec in Experiments 1 and 2, respectively.

CONCLUSIONS

The discriminative processes indexed by MMN in response to frequency changes areimmature in infants and preschool children. Although there is convincing evidence that the negativity elicited in Experiment 2 is an immature MMN, the possibility that it may be an "obligatory effect" indexing recovery from refractoriness cannot be ruled out at this time. The results from these experiments suggest that the MMN component haslimited use as a clinical tool at this time for infants and young children.

Mismatch negativity (MMN) as a tool for investigating auditory discrimination and sensory memory in infants and children

For decades behavioral methods, such as the head-turning or sucking paradigms, have been the primary methods to investigate auditory discrimination, learning and the function of sensory memory in infancy and early childhood. During recent years, however, a new method for investigating these issues in children has emerged. This method makes use of the mismatch negativity (MMN), the brain's automatic change-detection response, which has been used intensively in both basic and clinical studies in adults for twenty years. This review demonstrates that, unlike many other components of event-related potentials, the MMN is developmentally quite stable and can be obtained even from pre-term infants. Further, MMN amplitude is only slightly smaller in infants than is usually reported in school-age children and it does not seem to differ much from that obtained in adults. MMN latency has been reported to be slightly longer in infants than in adults but reaches adult values by the early school-age years. Child MMN does not seem to be analogous to adult MMN, however. For example, contrary to the results of adult studies, a prominent MMN can be obtained from in all waking- and sleep states in infants. Moreover, MMN scalp distribution seems to be broader and more central in children than in adults.

Quantitative analysis of discontinuous EEG in premature and full-term newborns during quiet sleep

To assess the spatio-temporal structure of discontinuous EEG tracing in mature and immature newborns, we analysed mean spectral power in frequency bands between 0.8 and 16.8 Hz in 6 full-term newborns and 7 premature newborns < 32 weeks of conceptional age. The most striking results showed a significantly higher mean spectral power for the first half of bursts than for the second half recorded in > 2.8-14.8 Hz frequency bands. This pattern was more pronounced in premature than in full-term newborns. No clear differences were observed in comparisons between the first and the second half of the interburst periods. In addition, as far as mid and high frequency band spectra were considered, the mean spectral power of burst was, in both groups, higher in the right as compared to the left occipital regions.

Effect of sleep stages on transiently evoked oto-acoustic emissions in infants

Transiently evoked oto-acoustic emissions (TEOAEs) are generated by active contractions of the outer hair cells (OHC) of the organ of Corti. TEOAE are inhibited by the medial efferent olivocochlear system which originates in the brainstem and innervates the OHC. TEOAEs are a rapid non-invasive objective method of auditory screening in infants. Because in infants sleep represents 75% of their time, it was of interest to determine whether sleep stages which are induced in the brainstem could concomitantly affect TEOAEs. Repeated TEOAE recordings during polygraphic recordings of sleep stages were made on seven, 6-week-old infants. Results showed that: (i) TEOAE spectrum frequency components remained stable over sleep stages; (ii) TEOAE amplitude tended to increase during recording sessions; (iii) sleep stages (quiet, active and indeterminate sleep) did not affect TEOAE amplitude. This pilot study reveals that sleep mechanisms seem to have no effect on active OHC micromechanical properties. Therefore, in auditory screening, TEOAEs may serve to study active cochlear mechanisms in infants even during sleep which is the better time to perform recordings because of the quietness required.