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.

Speech-Encoding Deficits in Neonates Born Large-for-Gestational Age as Revealed With the Envelope Frequency-Following Response.

OBJECTIVES: The present envelope frequency-following response (FFR ENV ) study aimed at characterizing the neural encoding of the fundamental frequency of speech sounds in neonates born at the higher end of the birth weight continuum (>90th percentile), known as large-for-gestational age (LGA). DESIGN: Twenty-five LGA newborns were recruited from the maternity unit of Sant Joan de Déu Barcelona Children's Hospital and paired by age and sex with 25 babies born adequate-for-gestational age (AGA), all from healthy mothers and normal pregnancies. FFR ENV s were elicited to the/da/ syllable and recorded while the baby was sleeping in its cradle after a successful universal hearing screening. Neural encoding of the stimulus' envelope of the fundamental frequency (F 0ENV ) was characterized through the FFR ENV spectral amplitude. Relationships between electrophysiological parameters and maternal/neonatal variables that may condition neonatal neurodevelopment were assessed, including pregestational body mass index (BMI), maternal gestational weight gain and neonatal BMI. RESULTS: LGA newborns showed smaller spectral amplitudes at the F 0ENV compared to the AGA group. Significant negative correlations were found between neonatal BMI and the spectral amplitude at the F 0ENV . CONCLUSIONS: Our results indicate that in spite of having a healthy pregnancy, LGA neonates' central auditory system is impaired in encoding a fundamental aspect of the speech sounds, namely their fundamental frequency. The negative correlation between the neonates' BMI and FFR ENV indicates that this impaired encoding is independent of the pregnant woman BMI and weight gain during pregnancy, supporting the role of the neonatal BMI. We suggest that the higher adipose tissue observed in the LGA group may impair, via proinflammatory products, the fine-grained central auditory system microstructure required for the neural encoding of the fundamental frequency of speech sounds.

Deficient neural encoding of speech sounds in term neonates born after fetal growth restriction.

Infants born after fetal growth restriction (FGR)-an obstetric condition defined as the failure to achieve the genetic growth potential-are prone to neurodevelopmental delays, with language being one of the major affected areas. Yet, while verbal comprehension and expressive language impairments have been observed in FGR infants, children and even adults, specific related impairments at birth, such as in the ability to encode the sounds of speech, necessary for language acquisition, remain to be disclosed. Here, we used the frequency-following response (FFR), a brain potential correlate of the neural phase locking to complex auditory stimuli, to explore the encoding of speech sounds in FGR neonates. Fifty-three neonates born with FGR and 48 controls born with weight adequate-for-gestational age (AGA) were recruited. The FFR was recorded to the consonant-vowel stimulus (/da/) during sleep and quantified as the spectral amplitude to the fundamental frequency of the syllable and its signal-to-noise ratio (SNR). The outcome was available in 45 AGA and 51 FGR neonates, yielding no differences for spectral amplitudes. However, SNR was strongly attenuated in the FGR group compared to the AGA group at the vowel region of the stimulus. These findings suggest that FGR population present a deficit in the neural pitch tracking of speech sounds already present at birth. Our results pave the way for future research on the potential clinical use of the FFR in this population, so that if confirmed, a disrupted FFR recorded at birth may help deriving FGR neonates at risk for postnatal follow-ups.

Neural generators of the frequency-following response elicited to stimuli of low and high frequency: A magnetoencephalographic (MEG) study.

The frequency-following response (FFR) to periodic complex sounds has gained recent interest in auditory cognitive neuroscience as it captures with great fidelity the tracking accuracy of the periodic sound features in the ascending auditory system. Seminal studies suggested the FFR as a correlate of subcortical sound encoding, yet recent studies aiming to locate its sources challenged this assumption, demonstrating that FFR receives some contribution from the auditory cortex. Based on frequency-specific phase-locking capabilities along the auditory hierarchy, we hypothesized that FFRs to higher frequencies would receive less cortical contribution than those to lower frequencies, hence supporting a major subcortical involvement for these high frequency sounds. Here, we used a magnetoencephalographic (MEG) approach to trace the neural sources of the FFR elicited in healthy adults (N = 19) to low (89 Hz) and high (333 Hz) frequency sounds. FFRs elicited to the high and low frequency sounds were clearly observable on MEG and comparable to those obtained in simultaneous electroencephalographic recordings. Distributed source modeling analyses revealed midbrain, thalamic, and cortical contributions to FFR, arranged in frequency-specific configurations. Our results showed that the main contribution to the high-frequency sound FFR originated in the inferior colliculus and the medial geniculate body of the thalamus, with no significant cortical contribution. In contrast, the low-frequency sound FFR had a major contribution located in the auditory cortices, and also received contributions originating in the midbrain and thalamic structures. These findings support the multiple generator hypothesis of the FFR and are relevant for our understanding of the neural encoding of sounds along the auditory hierarchy, suggesting a hierarchical organization of periodicity encoding.

Auditory predictions shape the neural responses to stimulus repetition and sensory change.

Perception is a highly active process relying on the continuous formulation of predictive inferences using short-term sensory memory templates, which are recursively adjusted based on new input. According to this idea, earlier studies have shown that novel stimuli preceded by a higher number of repetitions yield greater novelty responses, indexed by larger mismatch negativity (MMN). However, it is not clear whether this MMN memory trace effect is driven by more adapted responses to prior stimulation or rather by a heightened processing of the unexpected deviant, and only few studies have so far attempted to characterize the functional neuroanatomy of these effects. Here we implemented a modified version of the auditory frequency oddball paradigm that enables modeling the responses to both repeated standard and deviant stimuli. Fifteen subjects underwent functional magnetic resonance imaging (fMRI) while their attention was diverted from auditory stimulation. We found that deviants with longer stimulus history of standard repetitions yielded a more robust and widespread activation in the bilateral auditory cortex. Standard tones repetition yielded a pattern of response entangling both suppression and enhancement effects depending on the predictability of upcoming stimuli. We also observed that regularity encoding and deviance detection mapped onto spatially segregated cortical subfields. Our data provide a better understanding of the neural representations underlying auditory repetition and deviance detection effects, and further support that perception operates through the principles of Bayesian predictive coding.

Pattern-sensitive neurons reveal encoding of complex auditory regularities in the rat inferior colliculus.

A 'pattern alternation paradigm' has been previously used in human ERP recordings to investigate the brain encoding of complex auditory regularities, but prior studies on regularity encoding in animal models to examine mechanisms of adaptation of auditory neuronal responses have used primarily oddball stimulus sequences to study stimulus-specific adaptation alone. In order to examine the sensitivity of neuronal adaptation to expected and unexpected events embedded in a complex sound sequence, we used a similar patterned sequence of sounds. We recorded single unit activity and compared neuronal responses in the rat inferior colliculus (IC) to sound stimuli conforming to pattern alternation regularity with those to stimuli in which occasional sound repetitions violated that alternation. Results show that some neurons in the rat inferior colliculus are sensitive to the history of patterned stimulation and to violations of patterned regularity, demonstrating that there is a population of subcortical neurons, located as early as the level of the midbrain, that can detect more complex stimulus regularities than previously supposed and that are as sensitive to complex statistics as some neurons in primary auditory cortex. Our findings indicate that these pattern-sensitive neurons can extract temporal and spectral regularities between successive acoustic stimuli. This is important because the extraction of regularities from the sound sequences will result in the development of expectancies for future sounds and hence, the present results are compatible with predictive coding models. Our results demonstrate that some collicular neurons, located as early as in the midbrain level, are involved in the generation and shaping of prediction errors in ways not previously considered and thus, the present findings challenge the prevailing view that perceptual organization of sound only emerges at the auditory cortex level.

Involvement of the Serotonin Transporter Gene in Accurate Subcortical Speech Encoding.

A flourishing line of evidence has highlighted the encoding of speech sounds in the subcortical auditory system as being shaped by acoustic, linguistic, and musical experience and training. And while the heritability of auditory speech as well as nonspeech processing has been suggested, the genetic determinants of subcortical speech processing have not yet been uncovered. Here, we postulated that the serotonin transporter-linked polymorphic region (5-HTTLPR), a common functional polymorphism located in the promoter region of the serotonin transporter gene (SLC6A4), is implicated in speech encoding in the human subcortical auditory pathway. Serotonin has been shown as essential for modulating the brain response to sound both cortically and subcortically, yet the genetic factors regulating this modulation regarding speech sounds have not been disclosed. We recorded the frequency following response, a biomarker of the neural tracking of speech sounds in the subcortical auditory pathway, and cortical evoked potentials in 58 participants elicited to the syllable /ba/, which was presented >2000 times. Participants with low serotonin transporter expression had higher signal-to-noise ratios as well as a higher pitch strength representation of the periodic part of the syllable than participants with medium to high expression, possibly by tuning synaptic activity to the stimulus features and hence a more efficient suppression of noise. These results imply the 5-HTTLPR in subcortical auditory speech encoding and add an important, genetically determined layer to the factors shaping the human subcortical response to speech sounds. SIGNIFICANCE STATEMENT: The accurate encoding of speech sounds in the subcortical auditory nervous system is of paramount relevance for human communication, and it has been shown to be altered in different disorders of speech and auditory processing. Importantly, this encoding is plastic and can therefore be enhanced by language and music experience. Whether genetic factors play a role in speech encoding at the subcortical level remains unresolved. Here we show that a common polymorphism in the serotonin transporter gene relates to an accurate and robust neural tracking of speech stimuli in the subcortical auditory pathway. This indicates that serotonin transporter expression, eventually in combination with other polymorphisms, delimits the extent to which lifetime experience shapes the subcortical encoding of speech.

Selective entrainment of brain oscillations drives auditory perceptual organization.

Perceptual sound organization supports our ability to make sense of the complex acoustic environment, to understand speech and to enjoy music. However, the neuronal mechanisms underlying the subjective experience of perceiving univocal auditory patterns that can be listened to, despite hearing all sounds in a scene, are poorly understood. We hereby investigated the manner in which competing sound organizations are simultaneously represented by specific brain activity patterns and the way attention and task demands prime the internal model generating the current percept. Using a selective attention task on ambiguous auditory stimulation coupled with EEG recordings, we found that the phase of low-frequency oscillatory activity dynamically tracks multiple sound organizations concurrently. However, whereas the representation of ignored sound patterns is circumscribed to auditory regions, large-scale oscillatory entrainment in auditory, sensory-motor and executive-control network areas reflects the active perceptual organization, thereby giving rise to the subjective experience of a unitary percept.

Functional dissociation between regularity encoding and deviance detection along the auditory hierarchy.

Auditory deviance detection based on regularity encoding appears as one of the basic functional properties of the auditory system. It has traditionally been assessed with the mismatch negativity (MMN) long-latency component of the auditory evoked potential (AEP). Recent studies have found earlier correlates of deviance detection based on regularity encoding. They occur in humans in the first 50 ms after sound onset, at the level of the middle-latency response of the AEP, and parallel findings of stimulus-specific adaptation observed in animal studies. However, the functional relationship between these different levels of regularity encoding and deviance detection along the auditory hierarchy has not yet been clarified. Here we addressed this issue by examining deviant-related responses at different levels of the auditory hierarchy to stimulus changes varying in their degree of deviation regarding the spatial location of a repeated standard stimulus. Auditory stimuli were presented randomly from five loudspeakers at azimuthal angles of 0°, 12°, 24°, 36° and 48° during oddball and reversed-oddball conditions. Middle-latency responses and MMN were measured. Our results revealed that middle-latency responses were sensitive to deviance but not the degree of deviation, whereas the MMN amplitude increased as a function of deviance magnitude. These findings indicated that acoustic regularity can be encoded at the level of the middle-latency response but that it takes a higher step in the auditory hierarchy for deviance magnitude to be encoded, thus providing a functional dissociation between regularity encoding and deviance detection along the auditory hierarchy.

Repetition suppression and repetition enhancement underlie auditory memory-trace formation in the human brain: an MEG study.

The formation of echoic memory traces has traditionally been inferred from the enhanced responses to its deviations. The mismatch negativity (MMN), an auditory event-related potential (ERP) elicited between 100 and 250ms after sound deviation is an indirect index of regularity encoding that reflects a memory-based comparison process. Recently, repetition positivity (RP) has been described as a candidate ERP correlate of direct memory trace formation. RP consists of repetition suppression and enhancement effects occurring in different auditory components between 50 and 250ms after sound onset. However, the neuronal generators engaged in the encoding of repeated stimulus features have received little interest. This study intends to investigate the neuronal sources underlying the formation and strengthening of new memory traces by employing a roving-standard paradigm, where trains of different frequencies and different lengths are presented randomly. Source generators of repetition enhanced (RE) and suppressed (RS) activity were modeled using magnetoencephalography (MEG) in healthy subjects. Our results show that, in line with RP findings, N1m (~95-150ms) activity is suppressed with stimulus repetition. In addition, we observed the emergence of a sustained field (~230-270ms) that showed RE. Source analysis revealed neuronal generators of RS and RE located in both auditory and non-auditory areas, like the medial parietal cortex and frontal areas. The different timing and location of neural generators involved in RS and RE points to the existence of functionally separated mechanisms devoted to acoustic memory-trace formation in different auditory processing stages of the human brain.

Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulfate (DHEAS) and emotional processing - A behavioral and electrophysiological approach.

Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulfate (DHEAS) may have mood enhancement effects: higher DHEAS concentrations and DHEA/cortisol ratio have been related to lower depression scores and controlled trials of DHEA administration have reported significant antidepressant effects. The balance between DHEAS and DHEA has been suggested to influence brain functioning. We explored DHEAS, DHEA, cortisol, DHEA/cortisol and DHEAS/DHEA ratios relations to the processing of negative emotional stimuli at behavioral and brain levels by recording the electroencephalogram of 21 young women while performing a visual task with implicit neutral or negative emotional content in an audio-visual oddball paradigm. For each condition, salivary DHEA, DHEAS and cortisol were measured before performing the task and at 30 and 60min intervals. DHEA increased after task performance, independent of the implicit emotional content. With implicit negative emotion, higher DHEAS/DHEA and DHEA/cortisol ratios before task performance were related to shorter visual P300 latencies suggesting faster brain processing under a negative emotional context. In addition, higher DHEAS/DHEA ratios were related to reduced visual P300 amplitudes, indicating less processing of the negative emotional stimuli. With this study, we could show that at the electrophysiological level, higher DHEAS/DHEA and DHEA/cortisol ratios were related to shorter stimulus evaluation times suggesting less interference of the implicit negative content of the stimuli with the task. Furthermore, higher DHEAS/DHEA ratios were related to reduced processing of negative emotional stimuli which may eventually constitute a protective mechanism against negative information overload.

Two sequential processes of change detection in hierarchically ordered areas of the human auditory cortex.

Auditory deviance detection occurs around 150 ms after the onset of a deviant sound. Recent studies in animals and humans have described change-related processes occurring during the first 50 ms after sound onset. However, it still remains an open question whether these early and late processes of deviance detection are organized hierarchically in the human auditory cortex. We applied a beamforming source reconstruction approach in order to estimate brain sources associated with 2 temporally distinct markers of deviance detection. Results showed that rare frequency changes elicit an enhancement of the Nbm component of the middle latency response (MLR) peaking at 43 ms, in addition to the magnetic mismatch negativity (MMNm) peaking at 115 ms. Sources of MMNm, located in the right superior temporal gyrus, were lateral and posterior to the deviance-related MLR activity being generated in the right primary auditory cortex. Source reconstruction analyses revealed that detection of changes in the acoustic environment is a process accomplished in 2 different time ranges, by spatially separated auditory regions. Paralleling animal studies, our findings suggest that primary and secondary areas are involved in successive stages of deviance detection and support the existence of a hierarchical network devoted to auditory change detection.

Encoding of nested levels of acoustic regularity in hierarchically organized areas of the human auditory cortex.

Our auditory system is able to encode acoustic regularity of growing levels of complexity to model and predict incoming events. Recent evidence suggests that early indices of deviance detection in the time range of the middle-latency responses (MLR) precede the mismatch negativity (MMN), a well-established error response associated with deviance detection. While studies suggest that only the MMN, but not early deviance-related MLR, underlie complex regularity levels, it is not clear whether these two mechanisms interplay during scene analysis by encoding nested levels of acoustic regularity, and whether neuronal sources underlying local and global deviations are hierarchically organized. We registered magnetoencephalographic evoked fields to rapidly presented four-tone local sequences containing a frequency change. Temporally integrated local events, in turn, defined global regularities, which were infrequently violated by a tone repetition. A global magnetic mismatch negativity (MMNm) was obtained at 140-220 ms when breaking the global regularity, but no deviance-related effects were shown in early latencies. Conversely, Nbm (45-55 ms) and Pbm (60-75 ms) deflections of the MLR, and an earlier MMNm response at 120-160 ms, responded to local violations. Distinct neuronal generators in the auditory cortex underlay the processing of local and global regularity violations, suggesting that nested levels of complexity of auditory object representations are represented in separated cortical areas. Our results suggest that the different processing stages and anatomical areas involved in the encoding of auditory representations, and the subsequent detection of its violations, are hierarchically organized in the human auditory cortex.

Deviance detection based on regularity encoding along the auditory hierarchy: electrophysiological evidence in humans.

Detection of changes in the acoustic environment is critical for survival, as it prevents missing potentially relevant events outside the focus of attention. In humans, deviance detection based on acoustic regularity encoding has been associated with a brain response derived from the human EEG, the mismatch negativity (MMN) auditory evoked potential, peaking at about 100-200 ms from deviance onset. By its long latency and cerebral generators, the cortical nature of both the processes of regularity encoding and deviance detection has been assumed. Yet, intracellular, extracellular, single-unit and local-field potential recordings in rats and cats have shown much earlier (circa 20-30 ms) and hierarchically lower (primary auditory cortex, medial geniculate body, inferior colliculus) deviance-related responses. Here, we review the recent evidence obtained with the complex auditory brainstem response (cABR), the middle latency response (MLR) and magnetoencephalography (MEG) demonstrating that human auditory deviance detection based on regularity encoding-rather than on refractoriness-occurs at latencies and in neural networks comparable to those revealed in animals. Specifically, encoding of simple acoustic-feature regularities and detection of corresponding deviance, such as an infrequent change in frequency or location, occur in the latency range of the MLR, in separate auditory cortical regions from those generating the MMN, and even at the level of human auditory brainstem. In contrast, violations of more complex regularities, such as those defined by the alternation of two different tones or by feature conjunctions (i.e., frequency and location) fail to elicit MLR correlates but elicit sizable MMNs. Altogether, these findings support the emerging view that deviance detection is a basic principle of the functional organization of the auditory system, and that regularity encoding and deviance detection is organized in ascending levels of complexity along the auditory pathway expanding from the brainstem up to higher-order areas of the cerebral cortex.

That sounds awful! Does sound unpleasantness modulate the mismatch negativity and its habituation?

There are sounds that most people perceive as highly unpleasant, for instance, the sound of rubbing pieces of polystyrene together. Previous research showed larger physiological and neural responses for such aversive compared to neutral sounds. Hitherto, it remains unclear whether habituation, i.e., diminished responses to repeated stimulus presentation, which is typically reported for neutral sounds, occurs to the same extent for aversive stimuli. We measured the mismatch negativity (MMN) in response to rare occurrences of aversive or neutral deviant sounds within an auditory oddball sequence in 24 healthy participants, while they performed a demanding visual distractor task. Deviants occurred as single events (i.e., between two standards) or as double deviants (i.e., repeating the identical deviant sound in two consecutive trials). All deviants elicited a clear MMN, and amplitudes were larger for aversive than for neutral deviants (irrespective of their position within a deviant pair). This supports the claim of preattentive emotion evaluation during early auditory processing. In contrast to our expectations, MMN amplitudes did not show habituation, but increased in response to deviant repetition-similarly for aversive and neutral deviants. A more fine-grained analysis of individual MMN amplitudes in relation to individual arousal and valence ratings of each sound item revealed that stimulus-specific MMN amplitudes were best predicted by the interaction of deviant position and perceived arousal, but not by valence. Deviants with perceived higher arousal elicited larger MMN amplitudes only at the first deviant position, indicating that the MMN reflects preattentive processing of the emotional content of sounds.

The frequency-following response in late preterm neonates: a pilot study.

Introduction: Infants born very early preterm are at high risk of language delays. However, less is known about the consequences of late prematurity. Hence, the aim of the present study is to characterize the neural encoding of speech sounds in late preterm neonates in comparison with those born at term. Methods: The speech-evoked frequency-following response (FFR) was recorded to a consonant-vowel stimulus /da/ in 36 neonates in three different groups: 12 preterm neonates [mean gestational age (GA) 36.05 weeks], 12 "early term neonates" (mean GA 38.3 weeks), and "late term neonates" (mean GA 41.01 weeks). Results: From the FFR recordings, a delayed neural response and a weaker stimulus F0 encoding in premature neonates compared to neonates born at term was observed. No differences in the response time onset nor in stimulus F0 encoding were observed between the two groups of neonates born at term. No differences between the three groups were observed in the neural encoding of the stimulus temporal fine structure. Discussion: These results highlight alterations in the neural encoding of speech sounds related to prematurity, which were present for the stimulus F0 but not for its temporal fine structure.

Exposure to bilingual or monolingual maternal speech during pregnancy affects the neurophysiological encoding of speech sounds in neonates differently.

Introduction: Exposure to maternal speech during the prenatal period shapes speech perception and linguistic preferences, allowing neonates to recognize stories heard frequently in utero and demonstrating an enhanced preference for their mother's voice and native language. Yet, with a high prevalence of bilingualism worldwide, it remains an open question whether monolingual or bilingual maternal speech during pregnancy influence differently the fetus' neural mechanisms underlying speech sound encoding. Methods: In the present study, the frequency-following response (FFR), an auditory evoked potential that reflects the complex spectrotemporal dynamics of speech sounds, was recorded to a two-vowel /oa/ stimulus in a sample of 129 healthy term neonates within 1 to 3 days after birth. Newborns were divided into two groups according to maternal language usage during the last trimester of gestation (monolingual; bilingual). Spectral amplitudes and spectral signal-to-noise ratios (SNR) at the stimulus fundamental (F0) and first formant (F1) frequencies of each vowel were, respectively, taken as measures of pitch and formant structure neural encoding. Results: Our results reveal that while spectral amplitudes at F0 did not differ between groups, neonates from bilingual mothers exhibited a lower spectral SNR. Additionally, monolingually exposed neonates exhibited a higher spectral amplitude and SNR at F1 frequencies. Discussion: We interpret our results under the consideration that bilingual maternal speech, as compared to monolingual, is characterized by a greater complexity in the speech sound signal, rendering newborns from bilingual mothers more sensitive to a wider range of speech frequencies without generating a particularly strong response at any of them. Our results contribute to an expanding body of research indicating the influence of prenatal experiences on language acquisition and underscore the necessity of including prenatal language exposure in developmental studies on language acquisition, a variable often overlooked yet capable of influencing research outcomes.

Frequency-Following Responses in Sensorineural Hearing Loss: A Systematic Review.

PURPOSE: This systematic review aims to assess the impact of sensorineural hearing loss (SNHL) on various frequency-following response (FFR) parameters. METHODS: Following PRISMA guidelines, a systematic review was conducted using PubMed, Web of Science, and Scopus databases up to January 2023. Studies evaluating FFRs in patients with SNHL and normal hearing controls were included. RESULTS: Sixteen case-control studies were included, revealing variability in acquisition parameters. In the time domain, patients with SNHL exhibited prolonged latencies. The specific waves that were prolonged differed across studies. There was no consensus regarding wave amplitude in the time domain. In the frequency domain, focusing on studies that elicited FFRs with stimuli of 170 ms or longer, participants with SNHL displayed a significantly smaller fundamental frequency (F0). Results regarding changes in the temporal fine structure (TFS) were inconsistent. CONCLUSION: Patients with SNHL may require more time for processing (speech) stimuli, reflected in prolonged latencies. However, the exact timing of this delay remains unclear. Additionally, when presenting longer stimuli (≥ 170 ms), patients with SNHL show difficulties tracking the F0 of (speech) stimuli. No definite conclusions could be drawn on changes in wave amplitude in the time domain and the TFS in the frequency domain. Patient characteristics, acquisition parameters, and FFR outcome parameters differed greatly across studies. Future studies should be performed in larger and carefully matched subject groups, using longer stimuli presented at the same intensity in dB HL for both groups, or at a carefully determined maximum comfortable loudness level.

Novelty detection in the human auditory brainstem.

Auditory deviance detection has been associated with a human auditory-evoked potential (AEP), the mismatch negativity, generated in the auditory cortex 100-200 ms from sound change onset. Yet, single-unit recordings in animals suggest much earlier (∼20-40 ms), and anatomically lower (i.e., thalamus and midbrain) deviance detection. In humans, recordings of the scalp middle-latency AEPs have confirmed early (∼30-40 ms) deviance detection. However, involvement of the human auditory brainstem in deviance detection has not yet been demonstrated. Here we recorded the auditory brainstem frequency-following response (FFR) to consonant-vowel stimuli (/ba/, /wa/) in young adults, with stimuli arranged in oddball and reversed oddball blocks (deviant probability, p=0.2), allowing for the comparison of FFRs to the same physical stimuli presented in different contextual roles. Whereas no effect was observed for the /wa/ syllable, we found for the /ba/ syllable a reduction in the brainstem FFR to deviant stimuli compared with standard ones and to similar stimuli arranged in a control block, with five equiprobable, rarely occurring sounds. These findings demonstrate that the human auditory brainstem is able to encode regularities in the recent auditory past to detect novel events, and confirm the multiple anatomical and temporal scales of human deviance detection.