Cortical auditory event-related potentials in newborn infants

From psychophysiology to brain imaging: forty-five years MMN history of investigating acoustic change sensitivity

Forty-five years have passed since the first publication of the mismatch negativity (MMN) event-related brain potential (ERP) component. The first 10 years of research hardly gained any particular attention of the scientific community interested in acoustic perception. Debates on the nature of sensation versus perception were going on, and the technical possibilities to record ERPs, called in general evoked potentials, were very limited. Subtle changes in pure tone frequency or intensity giving rise to the MMN component were first investigated in humans. The background of the theoretical model developed by Risto Näätänen was the orientation reaction model of E.N. Sokolov published in 1963 so that the MMN was seen first as an electrophysiological correlate of auditory change detection. This fundamental ability of the auditory system seen as crucial for survival led to the development of the first animal model of the MMN (Csépe et al. in Clin Neurophysiol 66: 571-578, 1987). Indeed, it was confirmed that the MMN was the brain correlate of subtle changes detected that might alert to potential threats in the environment and direct the behavioral orientation. The investigations performed after 2000 introduced complex models and more sophisticated methods, both in animal and human studies, so that the MMN method was on the way to become a tool on the first place and not the main goal of research. This approach was further strengthened by the increasing number of studies on different clinical populations aiming at future applications. The aim of our review is to describe and redefine what the MMN may reflect in auditory perception and to show why and how this brain correlate of changes in the auditory scene can be used as a valuable tool in cognitive neuroscience research. We refer to publications selected to underly the argument the MMN cannot be classified anymore as a sign of simple change detection and not all the indicators used to confirm how genuine the MMN elicited by variations of tones are valid for those to  speech contrasts. We provide a fresh view on the broadly used MMN models, provided by some influential publications as well as on the unwritten history of MMN research aiming to give revised picture on what the MMN may truly reflect. We show how the focus and terminology of the MMN research have changed and what kind of misunderstandings and seemingly contradictive results prevent the MMN community to accept a generally usable cognitive model.

Mismatch negativity as a marker of music perception in individual cochlear implant users: A spike density component analysis study

OBJECTIVE

Ninety percent of cochlear implant (CI) users are interested in improving their music perception. However, only few objective behavioral and neurophysiological tests have been developed for tracing the development of music discrimination skills in CI users. In this study, we aimed to obtain an accurate individual mismatch negativity (MMN) marker that could predict behavioral auditory discrimination thresholds.

METHODS

We measured the individual MMN response to four magnitudes of deviations in four different musical features (intensity, pitch, timbre, and rhythm) in a rare sample of experienced CI users and a control sample of normally hearing participants. We applied a recently developed spike density component analysis (SCA), which can suppress confounding alpha waves, and contrasted it with previously proposed methods.

RESULTS

Statistically detected individual MMN predicted attentive sound discrimination ability with high accuracy: for CI users 89.2% (278/312 cases) and for controls 90.5% (384/424 cases). As expected, MMN was detected for fewer CI users when the sound deviants were of smaller magnitude.

CONCLUSIONS

The findings support the use of MMN responses in individual CI users as a diagnostic tool for testing music perception.

SIGNIFICANCE

For CI users, the new SCA method provided more accurate and replicable diagnostic detections than preceding state-of-the-art.

The Development and Neurophysiological Assessment of Newborn Auditory Cognition: A Review of Findings and Their Application

This review article introduces the basic principles of infants' neurophysiology, while summarizing the core knowledge of the anatomical structure of the auditory pathway, and presents previous findings on newborns' neural speech processing and suggests their possible applications for clinical practice. In order to tap into the functioning of the auditory pathway in newborns, recent approaches have employed electrophysiological techniques that measure electrical activity of the brain. The neural processing of an incoming auditory stimulus is objectively reflected by means of auditory event-related potentials. The newborn's nervous system processes the incoming sound, and the associated electrical activity of the brain is measured and extracted as components characterized by amplitude, latency, and polarity. Based on the parameters of event-related potentials, it is possible to assess the maturity of a child's brain, or to identify a pathology that needs to be treated or mitigated. For instance, in children with a cochlear implant, auditory event-related potentials are employed to evaluate an outcome of the implantation procedure and to monitor the development of hearing. Event-related potentials turn out to be an irreplaceable part of neurodevelopmental care for high-risk children e.g., preterm babies, children with learning disabilities, autism and many other risk factors.

Mismatch response in preterm and asphyxic neonates: a functional electrophysiological investigation of attention and habituation

BACKGROUND AND AIM

There is a lack of diagnostic tools for early risk stratification of cognitive outcome in infants born preterm and infants with asphyxia. Using auditory event-related potentials and mismatch response, we aimed to assess possible differences in early attention and learning, as a marker for brain maturation to subsequently improve the allocation of early neurodevelopmental support.

STUDY DESIGN AND METHODS

This cross-sectional study included 22 very preterm infants (gestational age (GA) < 32 weeks), eight term infants with asphyxia and 35 healthy term infants. An auditory oddball-paradigm with three consecutive stimulation blocks, separated by a two-minute break, was used as a cognitive discrimination task to assess attention and habituation.

RESULTS

The peak-to-peak analysis in the group comparisons showed no significant differences for the first stimulation block. In term healthy infants and term infants after asphyxia, no significant differences were found in amplitudes between block one and three. Preterm infants showed significantly (p = .007) lower amplitudes in the third block for F7 congruent to a positive habituation. The amplitude of the grouped electrodes correlated positively with GA for frontal (R = .271, p= .029) and parietal electrodes (R =.275, p = .027).

CONCLUSION

We found no differences in the auditory attention paradigm between preterm or term asphyxic and control infants when they were evaluated at term corrected age. Most infants did not show any electrophysiologically measurable learning effect indicating habituation or dishabituation. The small sample size of this study is a clear limitation. Therefore, the results must be evaluated with caution, especially regarding their potential predictive value for future cognitive development of infants with a developmental risk. However, our study underlines the possibility of an electrophysiological evaluation as a feasible tool to assess very early cognition in infants.

Short-term effects of single-dose chloral hydrate on neonatal auditory perception: An auditory event-related potential study

Objective

To study the short-term effects of a single-dose chloral hydrate on neonatal auditory perception by measuring auditory event-related potentials (aERPs).

Methods

Thirty-nine full-term neonates, aged 2–28 days and weighing 2980–4350 g, were divided into two groups including a chloral hydrate group (CH group, n = 17) and a non-chloral hydrate control group (non-CH group, n = 22). The CH group was given single-dose chloral hydrate (30 mg/kg) orally before aERPs measurement. An auditory oddball paradigm was used to elicit aERPs. P2 and N2 components of the ERP were recorded from electrodes at the Fz and Cz locations, and the areas under their curves (P2 and N2 areas) were calculated for the comparison between two groups.

Results

Significant differences was found in the P2 area between the two groups at Fz and Cz (Fz: F (1,37) = 487.75, P < 0.05; Cz: F (1,37) = 1465.94, P < 0.05). Similarly, significant difference was also in the N2 area between the two groups at both locations (Fz: F(1,37) = 153.38, P < 0.05; Cz: F(1,37) = 798.42, P < 0.05).

Conclusion

A single-dose of chloral hydrate impacts neonatal auditory perception in the short-term. Long-term effects will also be studied in future.

On the development of auditory distraction: A review

The present review focuses on the development of involuntary attention mechanisms in the context of the occurrence of unexpected events during childhood. We introduce a prevailing three-stage model of auditory involuntary attention describing the processes leading to, accompanying, and following the distraction of attention by prediction violations: (a) the automatic detection of prediction violations (associated with the event-related potential [ERP] component mismatch negativity [MMN]), (b) the involuntary orienting of attention processes towards the prediction violating sound (associated with the ERP component P3a), and (c) the reorienting back to task-relevant information (associated with the ERP components reorienting negativity [RON] or late discriminative negativity [LDN]). Within this framework we give an overview of studies investigating MMN, P3a, RON/LDN, and behavioral distraction effects in children. We discuss the development of the underlying involuntary attention mechanisms and highlight the relevance of and future perspectives for this important field of research.

Influence of gestational age and postnatal age on speech sound processing in NICU infants

The study examined the effect of gestational (GA) and postnatal (PNA) age on speech sound perception in infants. Auditory event-related potentials (ERPs) were recorded in response to speech sounds (syllables) in 50 infant NICU patients (born at 24-40 weeks gestation) prior to discharge. Efficiency of speech perception was quantified as absolute difference in mean amplitudes of ERPs in response to vowel (/a/-/u/) and consonant (/b/-/g/, /d/-/g/) contrasts within 150-250, 250-400, 400-700 ms after stimulus onset. Results indicated that both GA and PNA affected speech sound processing. These effects were more pronounced for consonant than vowel contrasts. Increasing PNA was associated with greater sound discrimination in infants born at or after 30 weeks GA, while minimal PNA-related changes were observed for infants with GA less than 30 weeks. Our findings suggest that a certain level of brain maturity at birth is necessary to benefit from postnatal experience in the first 4 months of life, and both gestational and postnatal ages need to be considered when evaluating infant brain responses.

The mismatch negativity (MMN)--a unique window to disturbed central auditory processing in ageing and different clinical conditions

In this article, we review clinical research using the mismatch negativity (MMN), a change-detection response of the brain elicited even in the absence of attention or behavioural task. In these studies, the MMN was usually elicited by employing occasional frequency, duration or speech-sound changes in repetitive background stimulation while the patient was reading or watching videos. It was found that in a large number of different neuropsychiatric, neurological and neurodevelopmental disorders, as well as in normal ageing, the MMN amplitude was attenuated and peak latency prolonged. Besides indexing decreased discrimination accuracy, these effects may also reflect, depending on the specific stimulus paradigm used, decreased sensory-memory duration, abnormal perception or attention control or, most importantly, cognitive decline. In fact, MMN deficiency appears to index cognitive decline irrespective of the specific symptomatologies and aetiologies of the different disorders involved.

Toward an electrocortical biomarker of cognition for newborn infants

The event-related potential (ERP) effect of mismatch negativity (MMN) was the first electrophysiological probe to evaluate cognitive processing (change detection) in newborn infants. Initial studies of MMN predicted clinical utility for this measure in identification of infants at risk for developmental cognitive deficits. These predictions have not been realized. We hypothesized that in sleeping newborn infants, measures derived from wavelet assessment of power in the MMN paradigm would be more robust markers of the brain's response to stimulus change than the ERP-derived MMN. Consistent with this premise, we found increased power in response to unpredictable and infrequent tones compared to frequent tones. These increases were present at multiple locations on the scalp over a range of latencies and frequencies and occurred even in the absence of an ERP-derived MMN. There were two predominant effects. First, theta band power was elevated at middle and late latencies (200 to 600 ms), suggesting that neocortical theta rhythms that subserve working memory in adults are present at birth. Second, late latency (500 ms) increased power to the unpredictable and infrequent tones was observed in the beta and gamma bands, suggesting that oscillations involved in adult cognition are also present in the neonate. These findings support the expectation that frequency dependent measures, such as wavelet power, will improve the prospects for a clinically useful test of cortical function early in the postnatal period.

Perinatal cerebral insults alter auditory event-related potentials

BACKGROUND

auditory event-related potentials (AERPs) can be used as indices of neural information processing. Altered AERPs have been reported in children and young adults with frontal lobe infarction.

AIM

to test the hypothesis that perinatal brain injury affects cortical auditory processing.

METHODS

we assessed AERPs at term, 6 and 12months of age in preterm infants [n=9, median gestational age (GA) 27.9, range 23.9-30.0wk], term infants with perinatal intracerebral hemorrhage (ICH) [n=5, GA 40.3, range 37.4-42.3wk], and term infants with perinatal asphyxia [n=4, GA 39.4, range 37.9-40.3wk]. Healthy preterm (n=16) and term infants (n=22) served as controls. A harmonic tone of 500-Hz frequency was used as standard and of 750-Hz as deviant stimulus. Mean AERP amplitudes were calculated over 100ms periods from 50 to 350ms. The developmental outcome was followed until 2years of age.

RESULTS

the term ICH (p=0.012) and asphyxia (p=0.0016) group had smaller or more negative responses to the deviant, resulting in smaller or more negative MMR amplitudes than those of the controls. The preterm ICH group did not differ significantly from their preterm born controls. MMR varied in all patient groups and was not associated with adverse outcome.

CONCLUSION

AERP alterations suggest that perinatal cerebral insults affect cortical auditory processing.

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.

Sensitivity of newborn auditory cortex to the temporal structure of sounds

Understanding the rapidly developing building blocks of speech perception in infancy requires a close look at the auditory prerequisites for speech sound processing. Pioneering studies have demonstrated that hemispheric specializations for language processing are already present in early infancy. However, whether these computational asymmetries can be considered a function of linguistic attributes or a consequence of basic temporal signal properties is under debate. Several studies in adults link hemispheric specialization for certain aspects of speech perception to an asymmetry in cortical tuning and reveal that the auditory cortices are differentially sensitive to spectrotemporal features of speech. Applying concurrent electrophysiological (EEG) and hemodynamic (near-infrared spectroscopy) recording to newborn infants listening to temporally structured nonspeech signals, we provide evidence that newborns process nonlinguistic acoustic stimuli that share critical temporal features with language in a differential manner. The newborn brain preferentially processes temporal modulations especially relevant for phoneme perception. In line with multi-time-resolution conceptions, modulations on the time scale of phonemes elicit strong bilateral cortical responses. Our data furthermore suggest that responses to slow acoustic modulations are lateralized to the right hemisphere. That is, the newborn auditory cortex is sensitive to the temporal structure of the auditory input and shows an emerging tendency for functional asymmetry. Hence, our findings support the hypothesis that development of speech perception is linked to basic capacities in auditory processing. From birth, the brain is tuned to critical temporal properties of linguistic signals to facilitate one of the major needs of humans: to communicate.

Timbre-independent extraction of pitch in newborn infants

The ability to separate pitch from other spectral sound features, such as timbre, is an important prerequisite of veridical auditory perception underlying speech acquisition and music cognition. The current study investigated whether or not newborn infants generalize pitch across different timbres. Perceived resonator size is an aspect of timbre that informs the listener about the size of the sound source, a cue that may be important already at birth. Therefore, detection of infrequent pitch changes was tested by recording event-related brain potentials in healthy newborn infants to frequent standard and infrequent pitch-deviant sounds while the perceived resonator size of all sounds was randomly varied. The elicitation of an early negative and a later positive discriminative response by deviant sounds demonstrated that the neonate auditory system represents pitch separately from timbre, thus showing advanced pitch processing capabilities.

Fetal magnetoencephalography

The assessment of the neurological integrity of the human fetus in utero is a technically challenging problem. New brain imaging devices can substantially improve our capabilities to describe functional brain activity in the fetus. It has been well established by fetal behavioral studies and investigations in preterm and term newborns that the brain is functional in utero. The major effort required to perform effective neurological functional investigations is designation of an integrated approach to neurological assessment and the generation of normative data. Currently, it is possible to record evoked brain activity elicited by auditory and visual stimulation from the fetus. In addition, there is growing evidence that spontaneous brain activity can be recorded in the fetus. This paper explores the current status of the brain-imaging field for fetal investigations and currently available data.

Magnetoencephalography of the newborn brain

This paper reviews the use of event-related magnetic fields (ERFs) in infants; ERFs can be derived from magnetoencephalography by means of averaging. Basic perceptive skills are important prerequisites for the infant's later development. The automatic cortical processes related to processing auditory, somatosensory and visual stimuli can be addressed by using responses recorded directly from the brain. The traditional method, the event-related potential (ERP), has recently been accompanied by ERFs. Similarly to ERPs, higher processes related to short-term memory, stimulus comparisons, and attention allocation can also be studied with ERFs. Further, since addressing the neonatal higher cognitive and social capabilities is challenging using only behavioural means, ERFs provide information on these important functions at a very early stage immediately after birth or in some cases even before birth. The main advantage of ERFs, compared to ERPs, is detection of the signals with high accuracy both with respect to the noise level and estimation of the spatial location.