Neonatal brainstem function and 4-month arousal-modulated attention are jointly associated with autism

Caregiver report of infant behavior associated with autism likelihood in first year of life

BACKGROUND

Identification of prodromal indicators of autism in infancy has the potential to identify behaviors relevant to early autism screening.

METHODS

We report on data from a prospective general population birth cohort with maternal reported measures at 9 and 12 months: the Survey of Well-Being of Young Children (SWYC; general developmental surveillance) and the First Year Inventory-Lite v3.1b (FYI-Lite; autism specific parent report research tool). Mothers completed the surveys and the Broad Autism Phenotype Questionnaire (BAPQ), a self-report measure of subclinical features of autism.

RESULTS

In this sample of 332 infants (168 males), maternal-reported infant developmental milestones and behavioral indicators of difficult temperament, poor adaptability, and sleep problems at 9 months (SWYC) and maternal self-reported subclinical autism characteristics (BAPQ) were correlated with maternal-reported autism-related behaviors on the FYI-Lite at 12 months. Regression models revealed significant unique associations between infant temperament, developmental milestones, and FYI-Lite scores while controlling for significant effects of maternal BAPQ scores and education.

CONCLUSIONS

Maternal report of infant temperament and developmental milestones at 9 months were associated with maternal-report early indicators of autism likelihood at 12 months in a general birth cohort. Follow up of this cohort is needed to determine associations with formal diagnostic outcomes.

IMPACT

Identifying scalable measures of infant behaviors in general and specific to autism may help identify targets of intervention for infants in the first year of life. This study aims to contribute to improved first-year surveillance by assessing potential early autism indicators in a prospective general birth cohort, whereas other observational studies utilize enriched risk cohorts (e.g., infant siblings of autistic children). Preliminary findings of this cohort revealed that a maternal report of 9-month temperament significantly predicted higher scores on a maternal report 12-month autism screener and indicated the importance of considering maternal self-reported subclinical autism characteristics when interpreting parent report screeners.

Exploring early life social and executive function development in infants and risk for autism: a prospective cohort study protocol of NICU graduates and infants at risk for cerebral palsy

BACKGROUND

Delays in early social and executive function are predictive of later developmental delays and eventual neurodevelopmental diagnoses. There is limited research examining such markers in the first year of life. High-risk infant groups commonly present with a range of neurodevelopmental challenges, including social and executive function delays, and show higher rates of autism diagnoses later in life. For example, it has been estimated that up to 30% of infants diagnosed with cerebral palsy (CP) will go on to be diagnosed with autism later in life.

METHODS

This article presents a protocol of a prospective longitudinal study. The primary aim of this study is to identify early life markers of delay in social and executive function in high-risk infants at the earliest point in time, and to explore how these markers may relate to the increased risk for social and executive delay, and risk of autism, later in life. High-risk infants will include Neonatal Intensive Care Unit (NICU) graduates, who are most commonly admitted for premature birth and/or cardiovascular problems. In addition, we will include infants with, or at risk for, CP. This prospective study will recruit 100 high-risk infants at the age of 3-12 months old and will track social and executive function across the first 2 years of their life, when infants are 3-7, 8-12, 18 and 24 months old. A multi-modal approach will be adopted by tracking the early development of social and executive function using behavioural, neurobiological, and caregiver-reported everyday functioning markers. Data will be analysed to assess the relationship between the early markers, measured from as early as 3-7 months of age, and the social and executive function as well as the autism outcomes measured at 24 months.

DISCUSSION

This study has the potential to promote the earliest detection and intervention opportunities for social and executive function difficulties as well as risk for autism in NICU graduates and/or infants with, or at risk for, CP. The findings of this study will also expand our understanding of the early emergence of autism across a wider range of at-risk groups.

Pre-autism: What a paediatrician should know about early diagnosis of autism‎

Autism, also known as an autism spectrum disorder, is a complex neurodevelopmental disorder usually diagnosed in the first three years of a child's life. A range of symptoms characterizes it and can be diagnosed at any age, including adolescence and adulthood. However, early diagnosis is crucial for effective management, prognosis, and care. Unfortunately, there are no established fetal, prenatal, or newborn screening programs for autism, making early detection difficult. This review aims to shed light on the early detection of autism prenatally, natally, and early in life, during a stage we call as "pre-autism" when typical symptoms are not yet apparent. Some fetal, neonatal, and infant biomarkers may predict an increased risk of autism in the coming baby. By developing a biomarker array, we can create an objective diagnostic tool to diagnose and rank the severity of autism for each patient. These biomarkers could be genetic, immunological, hormonal, metabolic, amino acids, acute phase reactants, neonatal brainstem function biophysical activity, behavioral profile, body measurements, or radiological markers. However, every biomarker has its accuracy and limitations. Several factors can make early detection of autism a real challenge. To improve early detection, we need to overcome various challenges, such as raising community awareness of early signs of autism, improving access to diagnostic tools, reducing the stigma attached to the diagnosis of autism, and addressing various culturally sensitive concepts related to the disorder.

Auditory Cortex Maturation and Language Development in Children with Hearing Loss and Additional Disabilities

A significant portion of hearing-impaired children have additional disabilities, but data about the maturation of their auditory cortex are scarce. In these children, behavioral tests are often unreliable, and objective tests are needed for diagnostics and follow-up. This study aimed to explore auditory cortical maturation and language development, and the usability of an objective electroencephalogram-based biomarker in children with multiple disabilities. In 65 hearing aid and cochlear implant users (36 females; 36 with multiple disabilities; 44.3 ± 18.5 months of age, mean ± SD), auditory processing was examined using the P1 cortical auditory evoked response biomarker, and language development with the Preschool Language Scales 5th edition (PLS-5). During the study, all of the children received intensive extra language therapy for six months. No significant differences were found between the groups in P1 latency development, the proportion of abnormal P1 latencies, or the number of children whose P1 latencies changed from abnormal to normal during the study. The PLS-5 total language scores, auditory comprehension scores, or expressive communication scores did not differ between groups either. The P1 latencies showed meaningful negative correlations with the language scores. The results suggest that auditory cortex development is similar in hearing-impaired children with/without additional disabilities, and the P1 biomarker is a feasible tool to evaluate central auditory maturation in children with multiple disabilities.

The first six months of life: A systematic review of early markers associated with later autism

There is now good evidence that behavioural signs of autism spectrum conditions (autism) emerge over the first two years of life. Identifying clear developmental differences early in life may facilitate earlier identification and intervention that can promote longer-term quality of life. Here we present a systematic review of studies investigating behavioural markers of later autism diagnosis or symptomology taken at 0-6 months. The following databases were searched for articles published between 01/01/2000 and 15/03/2022: Embase, Medline, Scopus, PubMed, PsycINFO, CINAHL, Web of Science and Proquest. Twenty-five studies met inclusion criteria: assessment of behaviour at 0-6 months and later assessment of autism symptomology or diagnosis. Studies examined behaviours of attention, early social and communication behaviours, and motor behaviours, as well as composite measures. Findings indicated some evidence of measures of general attention, attention to social stimuli, and motor behaviours associated with later autism diagnosis or symptomology. Findings were inconsistent regarding social and communication behaviours, with a lack of repeated or validated measures limiting drawing firm conclusions. We discuss implications of the findings and suggest recommendations for future research.

Newborn Auditory Brainstem Responses in Children with Developmental Disabilities

We integrated data from a newborn hearing screening database and a preschool disability database to examine the relationship between newborn click evoked auditory brainstem responses (ABRs) and developmental disabilities. This sample included children with developmental delay (n = 2992), speech impairment (SI, n = 905), language impairment (n = 566), autism spectrum disorder (ASD, n = 370), and comparison children (n = 128,181). We compared the phase of the ABR waveform, a measure of sound processing latency, across groups. Children with SI and children with ASD had greater newborn ABR phase values than both the comparison group and the developmental delay group. Newborns later diagnosed with SI or ASD have slower neurological responses to auditory stimuli, suggesting sensory differences at birth.

Sensitivity to interaural level and time differences in individuals with autism spectrum disorder

Individuals with autism spectrum disorders (ASD) are reported to exhibit degraded performance in sound localization. This study investigated whether the sensitivity to the interaural level differences (ILDs) and interaural time differences (ITDs), major cues for horizontal sound localization, are affected in ASD. Thresholds for discriminating the ILD and ITD were measured for adults with ASD and age- and IQ-matched controls in a lateralization experiment. Results show that the ASD group exhibited higher ILD and ITD thresholds than the control group. Moreover, there was a significant diversity of ITD sensitivity in the ASD group, and it contained a larger proportion of participants with poor ITD sensitivity than the control group. The current study suggests that deficits in relatively low-level processes in the auditory pathway are implicated in degraded performance of sound localization in individuals with ASD. The results are consistent with the structural abnormalities and great variability in the morphology in the brainstem reported by neuroanatomical studies of ASD.

Exploring brainstem auditory evoked potentials and mental development index as early indicators of autism spectrum disorders in high-risk infants

This study of infants from Hubei Province, China examined brainstem auditory evoked potentials (BAEP) and mental development index (MDI) as possible early indicators associated with autism spectrum disorders (ASD). The 34 ASD cases and 102 controls who had recovered from perinatal conditions were matched for age, sex, gestational age, birth weight and maternal age. BAEP absolute latencies (AL) I, III, V and interpeak latencies (IPL) I-III, III-V, I-V were compared in ASD cases and controls at ages 1, 3 and 6 months. MDI scores were compared in these infants from 1 month to 2 years old. Multiple logistic regression analysis was performed to test associations among ASD, BAEP and MDI. Results showed BAEP AL I, V and IPL III-V prolonged in the ASD group (p < 0.001), and MDI scores in ASD cases sharply declining from 12 to 24 months (p < 0.001). Regression analysis revealed odds ratios (OR) indicating that ASD was likely associated with abnormal values of BAEP AL I at 1 and 3 months (OR_{AL I} : 4.27; OR_{AL I} : 4.13), and AL V at 6 months (OR_{AL V} : 7.85). Lower MDI scores (MDI < 80) in infants at 1, 3, and 6 months were likely associated with ASD (OR_MDI : 2.58; OR_MDI : 3.83; OR_MDI : 4.87). These data show that abnormal BAEP values and low MDI scores are independent factors associated with ASD, and that monitoring of BAEP and MDI during infancy might facilitate screening for ASD development.

Pupil-Linked Arousal Response Reveals Aberrant Attention Regulation among Children with Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a developmental disorder that is characterized by difficulties with social interaction and interpersonal communication. It has been argued that abnormal attentional function to exogenous stimuli precedes and contributes to the core ASD symptoms. Notably, the locus ceruleus (LC) and its noradrenergic projections throughout the brain modulate attentional function, but the extent to which this locus ceruleus-norepinephrine (LC-NE) system influences attention in individuals with ASD, who frequently exhibit dysregulated alerting and attention orienting, is unknown. We examined dynamic attention control in girls and boys with ASD at rest using the pupil dilation response (PDR) as a noninvasive measure of LC-NE activity. When gender- and age-matched neurotypical participants were passively exposed to an auditory stream, their PDR decreased for recurrent stimuli but remained sensitive to surprising deviant stimuli. In contrast, children with ASD showed less habituation to recurrent stimuli as well as a diminished phasic response to deviants, particularly those containing social information. Their tonic habituation impairment predicts their phasic orienting impairment, and both impairments correlated with the severity of ASD symptom. Because of the fact that these pupil-linked responses are observed when individuals passively listen without any task engagement, our findings imply that the intricate and dynamic attention allocation mechanism, mediated by the subcortical LC-NE system, is impaired in ASD.SIGNIFICANCE STATEMENT Autistic individuals show attentional abnormalities to even simple sensory inputs, which emerge even before formal diagnosis. One possible mechanism behind these abnormalities is a malfunctioning pacemaker of their attention system, the locus ceruleus-norepinephrine pathway. Here we found, according to the pupillary response (a noradrenergic activity proxy), autistic children are hypersensitive to repeated sounds but hyposensitive to surprising deviant sounds when compared with age-matched controls. Importantly, hypersensitivity to repetitions predicts hyposensitivity to deviant sounds, and both abnormalities positively correlate to the severity of autistic symptoms. This provides strong evidence that autistic children have faulty noradrenergic regulation, which might underly the attentional atypicalities previously evidenced in various cortical responses in autistic individuals.

Click-evoked auditory brainstem responses and autism spectrum disorder: a meta-analytic investigation of disorder specificity

BACKGROUND

Click-evoked auditory brainstem response (ABR) alterations are associated with autism spectrum disorder (ASD), but the specificity of these findings to the disorder is unclear. We therefore performed a meta-analysis on ABRs and attention-deficit/hyperactivity disorder (ADHD), a neurodevelopmental disorder that shares some etiologic and symptom overlap with ASD.

METHODS

Seven papers compared ABR latency components (I, III, V, I-III, III-V, and I-V) between participants with and without ADHD. We used random-effects regression to generate component-specific estimates (Hedges's g) that adjusted for study sample sizes and the number of studies contributing to each estimate. We compared these estimates to our recently published meta-analysis of ABRs and ASD.

RESULTS

All ADHD studies employed cross-sectional designs. ADHD was associated with longer latencies for waves III and V (g = 0.6, 95% confidence interval (CI) 0.3, 1.0 and g = 0.6, 95% CI 0.3, 0.9) and waves I-III and I-V (g = 0.7, 95% CI 0.2, 1.3 and g = 0.6, 95% CI 0.3, 1.0). Effect sizes from the ASD and ADHD meta-analyses did not differ from each other.

CONCLUSIONS

Similar patterns of ABR alterations are observed in ADHD and ASD. However, studies rarely screen for middle ear dysfunction or hearing loss and rely upon cross-sectional designs. Addressing these issues will inform the viability of ABRs as a prognostic and/or etiologic biomarker for these disorders.

IMPACT

Click-evoked ABR alterations are associated with ASD, but the specificity of these findings to the disorder is unclear. We therefore performed a meta-analysis of the association between ABRs and ADHD, a disorder that shares some etiologic and symptom overlap with ASD. ADHD was associated with longer ABR latencies for several components. These components are identical to those implicated in ASD. Effect sizes were similar in magnitude across disorders. The viability of ABRs as prognostic and/or etiologic biomarkers for neurodevelopmental risk requires addressing limitations in the literature (e.g., cross-sectional data, non-standardized ABR protocols, minimal characterization of symptom heterogeneity).

A Systematic Review of Brainstem Contributions to Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that affects one in 66 children in Canada. The contributions of changes in the cortex and cerebellum to autism have been studied for decades. However, our understanding of brainstem contributions has only started to emerge more recently. Disruptions of sensory processing, startle response, sensory filtering, sensorimotor gating, multisensory integration and sleep are all features of ASD and are processes in which the brainstem is involved. In addition, preliminary research into brainstem contribution emphasizes the importance of the developmental timeline rather than just the mature brainstem. Therefore, the purpose of this systematic review is to compile histological, behavioral, neuroimaging, and electrophysiological evidence from human and animal studies about brainstem contributions and their functional implications in autism. Moreover, due to the developmental nature of autism, the review pays attention to the atypical brainstem development and compares findings based on age. Overall, there is evidence of an important role of brainstem disruptions in ASD, but there is still the need to examine the brainstem across the life span, from infancy to adulthood which could lead the way for early diagnosis and possibly treatment of ASD.

The Brainstem-Informed Autism Framework: Early Life Neurobehavioral Markers

Autism spectrum disorders (ASD) have long-term implications on functioning at multiple levels. In this perspective, we offer a brainstem-informed autism framework (BIAF) that traces the protracted neurobehavioral manifestations of ASD to early life brainstem dysfunctions. Early life brainstem-mediated markers involving functions of autonomic/arousal regulation, sleep-wake homeostasis, and sensorimotor integration are delineated. Their possible contributions to the early identification of susceptible infants are discussed. We suggest that the BIAF expands our multidimensional understanding of ASD by focusing on the early involvement of brainstem systems. Importantly, we propose an integrated BIAF screener that brings about the prospect of a sensitive and reliable early life diagnostic scheme for weighing the risk for ASD. The BIAF screener could provide clinicians substantial gains in the future and may carve customized interventions long before the current DSM ASD phenotype is manifested using dyadic co-regulation of brainstem-informed autism markers.

Auditory brainstem responses in adults with autism spectrum disorder

OBJECTIVE

To investigate possible differences in the auditory peripheral and brainstem functions between adults with autism spectrum disorder (ASD) and neurotypical (NT) adults.

METHODS

Click-evoked auditory brainstem responses (ABRs) were obtained from 17 high-functioning ASD adults (aged 21-38 years) and 20 NT adults (aged 22-36 years). A relatively large number of stimulus presentations (6000) were adopted, and ABRs by horizontal and vertical electrode montages were evaluated, in order to allow precise evaluations of early ABR components.

RESULTS

Waves I, II, III, and V were identified in the vertical electrode montage, and wave I and the summating potential (SP) in electrocochleograms were identified in the horizontal electrode montage. There were no significant group differences in the wave I, II, III, and V latencies or the interpeak latencies (IPLs) in the vertical electrode montage. In the horizontal montage, the ASD adults exhibited significantly shortened SP latencies compared with the NT adults, whereas there was no significant group difference in the wave I latency.

CONCLUSION

The ASD adults may have the abnormalities of processing more in the peripheral auditory system than in the brainstem.

SIGNIFICANCE

The current study suggests that the peripheral abnormality is associated with ASD.

Hyper-Reactivity to Salience Limits Social Interaction Among Infants Born Pre-term and Infant Siblings of Children With ASD

The ability to engage attention with selected stimuli is essential for infants to explore the world and process information relating to their surroundings. There are two main populations with a higher risk to develop attentional and social deficits whose deficits may arise from difficulties in regulating attention to salient cues: (1) siblings of children diagnosed with Autism; and (2) infants who were born pre-term. This study investigated infants' (N = 97) attention-engagement and pupil-dilation (PD) at 9 months of age, using a gaze-contingent paradigm and a structured social interaction. Specifically, we explored attention to stimuli with simple salient features (e.g., clear defined shapes, colors, and motions) vs. more complex non-social cues (amorphous shapes, colors, and motions) and social interaction in typically developing infants (TD, N = 25) and among two groups of infants at-risk to develop social difficulties (pre-terms, N = 56; siblings of children with Autism, N = 16). Findings show that the two risk groups preferred stimuli with simple features (F = 11.306, p < 0.001), accompanied by increased PD (F = 6.6, p < 0.001). Specifically, pre-term infants showed increased PD toward simple vs. complex stimuli (p < 0.001), while siblings showed a pervasive hyper-arousal to both simple and complex stimuli. Infants in the TD group preferred complex stimuli with no change in PD. Finally, the preference for the simple stimulus mediated the relationship between increased risk for social difficulties and decreased engagement duration in face-to-face interaction with the experimenter. Results suggest that activation of the attention-salience network shapes social abilities at infancy. Further, hyper-reactivity to salient stimuli limits social interaction among infants born pre-term and siblings of children with ASD.

Prolonged Auditory Brainstem Response in Universal Hearing Screening of Newborns with Autism Spectrum Disorder

Previous studies report prolonged auditory brainstem response (ABR) in children and adults with autism spectrum disorder (ASD). Despite its promise as a biomarker, it is unclear whether healthy newborns who later develop ASD also show ABR abnormalities. In the current study, we extracted ABR data on 139,154 newborns from their Universal Newborn Hearing Screening, including 321 newborns who were later diagnosed with ASD. We found that the ASD newborns had significant prolongations of their ABR phase and V‐negative latency compared with the non‐ASD newborns. Newborns in the ASD group also exhibited greater variance in their latencies compared to previous studies in older ASD samples, likely due in part to the low intensity of the ABR stimulus. These findings suggest that newborns display neurophysiological variation associated with ASD at birth. Future studies with higher‐intensity stimulus ABRs may allow more accurate predictions of ASD risk, which could augment the universal ABR test that currently screens millions of newborns worldwide.

Lay Summary

Children with autism spectrum disorder (ASD) have slow brain responses to sounds. We examined these brain responses from newborns' hearing tests and found that newborns who were later diagnosed with autism also had slower brain responses to sounds. Future studies might use these findings to better predict autism risk, with a hearing test that is already used on millions of newborns worldwide.

Autism spectrum disorder risk prediction: A systematic review of behavioral and neural investigations

A reliable diagnosis of autism spectrum disorder (ASD) is difficult to make until after toddlerhood. Detection in an earlier age enables early intervention, which is typically more effective. Recent studies of the development of brain and behavior in infants and toddlers have provided important insights in the diagnosis of autism. This extensive review focuses on published studies of predicting the diagnosis of autism during infancy and toddlerhood younger than 3 years using behavioral and neuroimaging approaches. After screening a total of 782 papers, 17 neuroimaging and 43 behavioral studies were reviewed. The features for prediction consist of behavioral measures using screening tools, observational and experimental methods, brain volumetric measures, and neural functional activation and connectivity patterns. The classification approaches include logistic regression, linear discriminant function, decision trees, support vector machine, and deep learning based methods. Prediction performance has large variance across different studies. For behavioral studies, the sensitivity varies from 20% to 100%, and specificity ranges from 48% to 100%. The accuracy rates range from 61% to 94% in neuroimaging studies. Possible factors contributing to this inconsistency may be partially due to the heterogeneity of ASD, different targeted populations (i.e., high-risk group for ASD and general population), age when the features were collected, and validation procedures. The translation to clinical practice requires extensive further research including external validation with large sample size and optimized feature selection. The use of multi-modal features, e.g., combination of neuroimaging and behavior, is worth further investigation to improve the prediction accuracy.

Prediction of Delayed Neurodevelopment in Infants Using Brainstem Auditory Evoked Potentials and the Bayley II Scales

Background: Brainstem auditory evoked potentials (BAEP) provide an objective analysis of central nervous system function and development in infants. This study proposed to examine the relationship between infant BAEP values at age 6 months, and their neurodevelopment at age 2 years assessed by the mental development indices (MDI), a form of Bayley Scales of Infant Development. We hypothesized that in infants with BAEP values outside normal range, there may be neurodevelopmental delays, as shown by their MDI scores. Methods: An exploratory investigation was conducted using preterm (28-36 weeks gestation; 95 cases) and term infants (≥37 weeks gestation; 100 cases) who were born with specific perinatal conditions. BAEP values were recorded in these infants from 1 to 8 months of age, and compared with MDI scores in these infants at age 2 years. A multivariate linear regressions model was performed to test the associations between all variables and MDI scores. Stratified linear regression was used to test the interactions between gestational age and BAEP values with MDI scores. Significance was determined at a p < 0.05. Results: We found that BAEP values were inversely associated with MDI scores in premature infants (β = -1.89; 95% confidence interval = -3.42 to -0.36), and that the effect of gestational age and BAEP values on the MDI scores is decreased by 1.89 points due to the interaction between these two variables. In premature babies, the lower the BAEP value below the mean, the greater the decrease in MDI score at age 2 years. Asphyxia and lower socioeconomic status in the family were also covariates associated with lower MDI scores at age 2 years. Conclusion: The data provided evidence that BAEP values outside the normal range in premature infants at age 6 months may predict developmental delays in cognitive and motor skills, as shown by MDI scores. We propose that BAEP assessment may be utilized as a potential indicator for neurodevelopment, and suggest that early intellectual and public health interventions should be encouraged to enrich neurodevelopment in premature babies with BAEP values outside the normal range.

Expanding the critique of the social motivation theory of autism with participatory and developmental research

We argue that understanding of autism can be strengthened by increasing involvement of autistic individuals as researchers and by exploring cascading impacts of early sensory, perceptual, attentional, and motor atypicalities on social and communicative developmental trajectories. Participatory action research that includes diverse participants or researchers may help combat stigma while expanding research foci to better address autistic people's needs.

Diagnostic Assessment Techniques and Non-Invasive Biomarkers for Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex heterogeneous neurological disorder that has led to a spectrum of diagnosis techniques. The screening instruments, medical and technological tools initiate the diagnosis process. Clinicians and psychologists propose therapies depending on the examination done by these methodologies. The literature has accounted dozens of diagnostic methods and alternative and complementary therapies but still lack in highlighting the proper biomarker for early detection and intervention. The emerging multi-modal neuro-imaging techniques have correlated the brain's functional and structural measures and diagnosed ASD with more sensitivity than individual approaches. The purpose of this review article is: (i) to provide an overview of the emerging ASD diagnosis methods and different markers and; (ii) to present the idea of integrating all the individual methods in to a multi-modal diagnostic system to enhance detection sensitivity. This system possesses the potential to diagnose and predict ASD clinically, neurologically & objectively with high detection sensitivity.

Auditory Brainstem Pathology in Autism Spectrum Disorder: A Review

Atypical responses to sound are common in individuals with autism spectrum disorder (ASD), and growing evidence suggests an underlying auditory brainstem pathology. This review of the literature provides a comprehensive account of the structural and functional evidence for auditory brainstem abnormalities in ASD. The studies reviewed were published between 1975 and 2016 and were sourced from multiple online databases. Indices of both the quantity and quality of the studies reviewed are considered. Findings show converging evidence for auditory brainstem pathology in ASD, although the specific functions and anatomical structures involved remain equivocal. Two main trends emerge from the literature: (1) abnormalities occur mainly at higher levels of the auditory brainstem, according to structural imaging and electrophysiology studies; and (2) brainstem abnormalities appear to be more common in younger than older children with ASD. These findings suggest delayed maturation of neural transmission pathways between lower and higher levels of the brainstem and are consistent with the auditory disorders commonly observed in ASD, including atypical sound sensitivity, poor sound localization, and difficulty listening in background noise. Limitations of existing studies are discussed, and recommendations for future research are offered.

Evidence for Brainstem Contributions to Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental condition that affects one in 59 children in the United States. Although there is a mounting body of knowledge of cortical and cerebellar contributions to ASD, our knowledge about the early developing brainstem in ASD is only beginning to accumulate. Understanding how brainstem neurotransmission is implicated in ASD is important because many of this condition’s sensory and motor symptoms are consistent with brainstem pathology. Therefore, the purpose of this review was to integrate epidemiological, behavioral, histological, neuroimaging, and animal evidence of brainstem contributions to ASD. Because ASD is a neurodevelopmental condition, we examined the available data through a lens of hierarchical brain development. The review of the literature suggests that developmental alterations of the brainstem could have potential cascading effects on cortical and cerebellar formation, ultimately leading to ASD symptoms. This view is supported by human epidemiology findings and data from animal models of ASD, showing that perturbed development of the brainstem substructures, particularly during the peak formation of the brainstem’s monoaminergic centers, may relate to ASD or ASD-like behaviors. Furthermore, we review evidence from human histology, psychophysiology, and neuroimaging suggesting that brainstem development and maturation may be atypical in ASD and may be related to key ASD symptoms, such as atypical sensorimotor features and social responsiveness. From this review there emerges the need of future research to validate early detection of the brainstem-based somatosensory and psychophysiological behaviors that emerge in infancy, and to examine the brainstem across the life span, while accounting for age. In all, there is preliminary evidence for brainstem involvement in ASD, but a better understanding of the brainstem’s role would likely pave the way for earlier diagnosis and treatment of ASD.

Click-evoked auditory brainstem responses and autism spectrum disorder: A meta-analytic review

Behavior does not differentiate ASD risk prior to 12 months of age, but biomarkers may inform risk before symptoms emerge. Click-evoked auditory brainstem responses (ABRs) may be worth consideration due to their measurement properties (noninvasiveness; reliability) and conceptual features (well-characterized neural generators), but participant characteristics and assessment protocols vary considerably across studies. Our goal is to perform a meta-analysis of the association between ABRs and ASD. Following an electronic database search (PubMed, Medline, PsycInfo, PsycArticles), we included papers that were written in English, included ASD and typically-developing (TD) groups, and reported the information needed to calculate standardized mean differences (Hedges's g) for at least one ABR latency component (I, III, V, I-III, III-V, I-V). We weighted and averaged effect sizes across conditions and subsets of participants to yield one estimate per component per study. We then performed random-effects regressions to generate component-specific estimates. ASD was associated with longer ABR latencies for Waves III (g = 0.5, 95% CI 0.1, 0.9), V (g = 0.7, 95% CI 0.3, 1.1), I-III (g = 0.7, 95% CI 0.2, 1.2), and I-V (g = 0.6, 95% CI 0.2, 1.0). All components showed significant heterogeneity. Associations were strongest among participants ≤8 years of age and those without middle ear abnormalities or elevated auditory thresholds. In sum, associations between ABRs and ASD are medium-to-large in size, but exhibit heterogeneity. Identifying sources of heterogeneity is challenging, however, due to power limitations and co-occurrence of sample/design characteristics across studies. Research addressing the above limitations is crucial to determining the etiologic and/or prognostic value of ABRs for ASD. Autism Res 2018, 11: 916-927. © 2018 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

Auditory brainstem responses (ABR) may be associated with ASD, but participant characteristics and assessment protocols vary considerably across individual studies. Our goal is to combine the results across these studies to facilitate clarity on the topic. Doing so represents a first step in evaluating whether ABRs yield potential for informing the etiology of ASD risk and/or ASD symptom profiles.

Auditory brainstem response in infants and children with autism spectrum disorder: A meta-analysis of wave V

Infants with autism spectrum disorder (ASD) were recently found to have prolonged auditory brainstem response (ABR); however, at older ages, findings are contradictory. We compared ABR differences between participants with ASD and controls with respect to age using a meta-analysis. Data sources included MEDLINE, EMBASE, Web of Science, Google Scholar, HOLLIS, and ScienceDirect from their inception to June 2016. The 25 studies that were included had a total of 1349 participants (727 participants with ASD and 622 controls) and an age range of 0-40 years. Prolongation of the absolute latency of wave V in ASD had a significant negative correlation with age (R2 = 0.23; P = 0.01). The 22 studies below age 18 years showed a significantly prolonged wave V in ASD (Standard Mean Difference = 0.6 [95% CI, 0.5-0.8]; P < 0.001). The 3 studies above 18 years of age showed a significantly shorter wave V in ASD (SMD = -0.6 [95% CI, -1.0 to -0.2]; P = 0.004). Prolonged ABR was consistent in infants and children with ASD, suggesting it can serve as an ASD biomarker at infancy. As the ABR is routinely used to screen infants for hearing impairment, the opportunity for replication studies is extensive. Autism Res 2018, 11: 355-363. © 2017 The Authors Autism Research published by International Society for Autism Research and Wiley Periodicals, Inc.

LAY SUMMARY

Our analysis of previous studies showed that infants and children with autism spectrum disorder (ASD) have a slower brain response to sound, while adults have a faster brain response to sound. This suggests that slower brain response in infants may predict ASD risk. Brain response to sound is routinely tested on newborns to screen hearing impairment, which has created large data sets to afford replication of these results.

Brainstem as a developmental gateway to social attention

BACKGROUND

Evolution preserves social attention due to its key role in supporting survival. Humans are attracted to social cues from infancy, but the neurobiological mechanisms for the development of social attention are unknown. An evolutionary-based, vertical-hierarchical theoretical model of self-regulation suggests that neonatal brainstem inputs are key for the development of well-regulated social attention.

METHODS

Neonates born preterm (N = 44, GA 34 w.) were recruited and diagnosed at birth as a function of their auditory brainstem evoked responses (ABR). Participants enrolled in a prospective 8-year-long, double-blind, follow-up study comparing participants with brainstem dysfunctions and well-matched controls. Groups had comparable fetal, neonatal, and familial characteristics. Methods incorporated EEG power analysis and gaze tracking during the Attention Network Test (ANT, four cue types, and two targets) and a Triadic Gaze Engagement task (TGE, three social cue levels).

RESULTS

Results showed that neonatal brainstem compromise is related to long-term changes in Alpha- and Theta-band power asymmetries (p < .034, p < .016, respectively), suggesting suppressed bottom-up input needed to alert social attention. Gaze tracking indicated dysregulated arousal-modulated attention (p < .004) and difficulty in gaze engagement to socially neutral compared to nonsocial cues (p < .012).

CONCLUSIONS

Integrating models of Autism and cross-species data with current long-term follow-up of infants with discrete neonatal brainstem dysfunction suggests neonatal brainstem input as a gateway for bottom-up regulation of social attention.

Toward a conceptual framework for early brain and behavior development in autism

Studies of infant siblings of older autistic probands, who are at elevated risk for autism, have demonstrated that the defining features of autism are not present in the first year of life but emerge late in the first and into the second year. A recent longitudinal neuroimaging study of high-risk siblings revealed a specific pattern of brain development in infants later diagnosed with autism, characterized by cortical surface area hyper-expansion in the first year followed by brain volume overgrowth in the second year that is associated with the emergence of autistic social deficits. Together with new observations from genetically defined autism risk alleles and rodent model, these findings suggest a conceptual framework for the early, post-natal development of autism. This framework postulates that an increase in the proliferation of neural progenitor cells and hyper-expansion of cortical surface area in the first year, occurring during a pre-symptomatic period characterized by disrupted sensorimotor and attentional experience, leads to altered experience-dependent neuronal development and decreased elimination of neuronal processes. This process is linked to brain volume overgrowth and disruption of the refinement of neural circuit connections and is associated with the emergence of autistic social deficits in the second year of life. A better understanding of the timing of developmental brain and behavior mechanisms in autism during infancy, a period which precedes the emergence of the defining features of this disorder, will likely have important implications for designing rational approaches to early intervention.

Neurodevelopmental Hypothesis about the Etiology of Autism Spectrum Disorders

Previous models or hypotheses of autism spectral disorder (ASD) failed to take into full consideration the chronological and causal developmental trajectory, leading to the emergence of diverse phenotypes through a complex interaction between individual etiologies and environmental factors. Those phenotypes include persistent deficits in social communication and social interaction (criteria A in DSM-5), and restricted, repetitive patterns of behavior, interests, or activities (criteria B in DSM-5). In this article, we proposed a domain-general model that can explain criteria in DSM-5 based on the assumption that the same etiological mechanism would trigger the various phenotypes observed in different individuals with ASD. In the model, we assumed the following joint causes as the etiology of autism: (1) Hypoplasia of the pons in the brainstem, occurring immediately following neural tube closure; and (2) Deficiency in the GABA (γ-aminobutyric acid) developmental switch during the perinatal period. Microstructural abnormalities of the pons directly affect both the structural and functional development of the brain areas strongly connected to it, especially amygdala. The impairment of GABA switch could not only lead to the deterioration of inhibitory processing in the neural network, but could also cause abnormal cytoarchitecture. We introduced a perspective that atypical development in both brain structure and function can give full explanation of diverse phenotypes and pathogenetic mechanism of ASD. Finally, we discussed about neural mechanisms underlying the phenotypic characteristics of ASD that are not described in DSM-5 but should be considered as important foundation: sleep, global precedence, categorical perception, intelligence, interoception and motor control.

The Autism Parent Screen for Infants: Predicting risk of autism spectrum disorder based on parent-reported behavior observed at 6–24 months of age

This study examined whether a novel parent-report questionnaire, the Autism Parent Screen for Infants, could differentiate infants subsequently diagnosed with autism spectrum disorder from a high-risk cohort (siblings of children diagnosed with autism spectrum disorder (n = 66)) from high-risk and low-risk comparison infants (no family history of autism spectrum disorder) who did not develop autism spectrum disorder (n = 138 and 79, respectively). Participants were assessed prospectively at 6, 9, 12, 15, 18, and 24 months of age. At 36 months, a blind independent diagnostic assessment for autism spectrum disorder was completed. Parent report on the Autism Parent Screen for Infants was examined in relation to diagnostic outcome and risk status (i.e. high-risk sibling with autism spectrum disorder, high-risk sibling without autism spectrum disorder, and low-risk control). The results indicated that from 6 months of age, total score on the Autism Parent Screen for Infants differentiated between the siblings with autism spectrum disorder and the other two groups. The sensitivity, specificity, and positive and negative predictive validity of the Autism Parent Screen for Infants highlight its potential for the early screening of autism spectrum disorder in high-risk cohorts.

Brainstem White Matter Predicts Individual Differences in Manual Motor Difficulties and Symptom Severity in Autism

Mounting evidence suggests that poorer motor skills may be related to more severe autism symptoms. This study investigated if atypical white matter microstructure in the brain mediated the relationship between motor skills and ASD symptom severity. Sixty-seven males with ASD and 42 males with typical development (5-33 years old) completed a diffusion tensor imaging scan and measures of grip strength, finger tapping, and autism symptom severity. Within the ASD group, weaker grip strength predicted more severe autism symptoms. Fractional anisotropy of the brainstem's corticospinal tract predicted both grip strength and autism symptom severity and mediated the relationship between the two. These findings suggest that brainstem white matter may contribute to autism symptoms and grip strength in ASD.

Prolonged auditory brainstem responses in infants with autism

Numerous studies have attempted to identify early physiological abnormalities in infants and toddlers who later develop autism spectrum disorder (ASD). One potential measure of early neurophysiology is the auditory brainstem response (ABR), which has been reported to exhibit prolonged latencies in children with ASD. We examined whether prolonged ABR latencies appear in infancy, before the onset of ASD symptoms, and irrespective of hearing thresholds. To determine how early in development these differences appear, we retrospectively examined clinical ABR recordings of infants who were later diagnosed with ASD. Of the 118 children in the participant pool, 48 were excluded due to elevated ABR thresholds, genetic aberrations, or old testing age, leaving a sample of 70 children: 30 of which were tested at 0–3 months, and 40 were tested at toddlerhood (1.5–3.5 years). In the infant group, the ABR wave‐V was significantly prolonged in those who later developed ASD as compared with case‐matched controls (n = 30). Classification of infants who later developed ASD and case‐matched controls using this measure enabled accurate identification of ASD infants with 80% specificity and 70% sensitivity. In the group of toddlers with ASD, absolute and interpeak latencies were prolonged compared to clinical norms. Findings indicate that ABR latencies are significantly prolonged in infants who are later diagnosed with ASD irrespective of their hearing thresholds; suggesting that abnormal responses might be detected soon after birth. Further research is needed to determine if ABR might be a valid marker for ASD risk. Autism Res2016, 9: 689–695. © 2015 The Authors Autism Research published by Wiley Periodicals, Inc. on behalf of International Society for Autism Research

Can parents' concerns predict autism spectrum disorder? A prospective study of high-risk siblings from 6 to 36 months of age

OBJECTIVE

This prospective study characterized parents' concerns about infants at high risk for developing autism spectrum disorder (ASD; each with an older sibling with ASD) at multiple time points in the first 2 years, and assessed their relation to diagnostic outcome at 3 years.

METHOD

Parents of low-risk controls (LR) and high-risk infant siblings (HR) reported any concerns that they had regarding their children's development between 6 and 24 months of age regarding sleep, diet, sensory behavior, gross/fine motor skills, repetitive movements, communication, communication regression, social skills, play, and behavioral problems, using a parent concern form designed for this study. At 3 years of age, an independent, gold-standard diagnostic assessment for ASD was conducted for all participants.

RESULTS

As predicted, parents of HR children who received an ASD diagnosis reported more concerns than parents of LR and HR children who did not have ASD. The total number of concerns predicted a subsequent diagnosis of ASD as early as 12 months within the HR group. Concerns regarding sensory behavior and motor development predicted a subsequent diagnosis of ASD as early as 6 months, whereas concerns about social communication and repetitive behaviors did not predict diagnosis of ASD until after 12 months.

CONCLUSION

Parent-reported concerns can improve earlier recognition of ASD in HR children.

Annual research review: Infant development, autism, and ADHD--early pathways to emerging disorders

BACKGROUND

Autism spectrum disorders (ASD) and attention deficit hyperactivity disorder (ADHD) are two of the most common neurodevelopmental disorders, with a high degree of co-occurrence.

METHODS

Prospective longitudinal studies of infants who later meet criteria for ASD or ADHD offer the opportunity to determine whether the two disorders share developmental pathways.

RESULTS

Prospective studies of younger siblings of children with autism have revealed a range of infant behavioral and neural markers associated with later diagnosis of ASD. Research on infants with later ADHD is less developed, but emerging evidence reveals a number of relations between infant measures and later symptoms of inattention and hyperactivity.

CONCLUSIONS

We review this literature, highlighting points of convergence and divergence in the early pathways to ASD and ADHD.

Neonatal brainstem dysfunction after preterm birth predicts behavioral inhibition

BACKGROUND

Behavioral inhibition (BI), the tendency to withdraw or exhibit negative affect when experiencing stressful situations, is a major risk factor for the development of social anxiety. However, neonatal biologic origins of this progression are still unknown. Click here to enter text.This study aimed to extend frameworks of behavioral inhibition by exploring empirically the central role of neonatal brainstem electrophysiologic functions in the development of social disengagement and BI.

METHODS

Sixty-six preterm neonates (means ±SD: gestation age = 33.1 ± 1.22 weeks, birth weight = 1775 + 346.7 g; 51% female) participated in a prospective longitudinal study. The infants were tested within the first 2 weeks of postnatal life using an auditory brainstem-evoked response test. Based on the typicality of the major ABR wave latencies, waves I, III and V, neonates were divided into two groups (compromised, CBSF- with at least one component ≥1.5 SDs from the mean for the respective gestation age; normal, NBSF, with all components within 1.5 SD around the mean), and were enrolled in a prospective longitudinal follow-up study. This report extends previous work from 4 m by testing responses to socioemotional challenges during the Separation-Reunion paradigm at 12 m.

RESULTS

Results show that infants with neonatal CBSF were more susceptible to be classified as BI at 12 m (age corrected for prematurity) than infants with NBSF (66% vs. 40%, respectively). The most striking symptom in the CBSF group was a disability to initiate self-regulatory activities in response to a socioemotional challenge, resulting in frequent passivity/dependency (p < .001). Statistical regression analysis revealed that face-to-face gaze engagement at 4 m moderates the risk related to neonatal CBSF for the emergence of BI at 12 m, but did not overturn the emergence of BI.

CONCLUSION

Results support the hypothesis that neonatal brainstem dysfunction canalizes behavioral inhibition. These findings highlight, for the first time, the role of the early developing brainstem in later development of BI and in abilities to initiate self-regulatory behavior.

Arousal and attention re-orienting in autism spectrum disorders: evidence from auditory event-related potentials

The extended phenotype of autism spectrum disorders (ASD) includes a combination of arousal regulation problems, sensory modulation difficulties, and attention re-orienting deficit. A slow and inefficient re-orienting to stimuli that appear outside of the attended sensory stream is thought to be especially detrimental for social functioning. Event-related potentials (ERPs) and magnetic fields (ERFs) may help to reveal which processing stages underlying brain response to unattended but salient sensory event are affected in individuals with ASD. Previous research focusing on two sequential stages of the brain response-automatic detection of physical changes in auditory stream, indexed by mismatch negativity (MMN), and evaluation of stimulus novelty, indexed by P3a component,-found in individuals with ASD either increased, decreased, or normal processing of deviance and novelty. The review examines these apparently conflicting results, notes gaps in previous findings, and suggests a potentially unifying hypothesis relating the dampened responses to unattended sensory events to the deficit in rapid arousal process. Specifically, "sensory gating" studies focused on pre-attentive arousal consistently demonstrated that brain response to unattended and temporally novel sound in ASD is already affected at around 100 ms after stimulus onset. We hypothesize that abnormalities in nicotinic cholinergic arousal pathways, previously reported in individuals with ASD, may contribute to these ERP/ERF aberrations and result in attention re-orienting deficit. Such cholinergic dysfunction may be present in individuals with ASD early in life and can influence both sensory processing and attention re-orienting behavior. Identification of early neurophysiological biomarkers for cholinergic deficit would help to detect infants "at risk" who can potentially benefit from particular types of therapies or interventions.

Speech disturbs face scanning in 6-month-old infants who develop autism spectrum disorder

BACKGROUND

From birth, infants show a preference for the faces, gaze, and voices of others. In individuals with autism spectrum disorders (ASDs) these biases seem to be disturbed. The source of these disturbances is not well-understood, but recent efforts have shown that the spontaneous deployment of attention to social targets might be atypical as early as 6 months of age. The nature of this atypical behavior and the conditions under which it arises are currently unknown.

METHODS

We used eye-tracking to examine the gaze patterns of 6-month-old infants (n = 99) at high risk (n = 57) and low risk (n = 42) for developing ASD as they viewed faces that were: 1) still; 2) moving and expressing positive affect; or 3) speaking. Clinical outcomes were determined through a comprehensive assessment at the age of 3 years. The scanning patterns of infants later diagnosed with ASD were compared with infants without an ASD outcome.

RESULTS

Infants who later developed ASD spent less time looking at the presented scenes in general than other infants. When these infants looked at faces, their looking toward the inner features of faces decreased compared with the other groups only when the presented face was speaking.

CONCLUSIONS

Our study suggests that infants later diagnosed with ASD have difficulties regulating attention to complex social scenes. It also suggests that the presence of speech might uniquely disturb the attention of infants who later develop ASD at a critical developmental point when other infants are acquiring language and learning about their social world.

Developmental pathways to autism: a review of prospective studies of infants at risk

Autism Spectrum Disorders (ASDs) are neurodevelopmental disorders characterized by impairments in social interaction and communication, and the presence of restrictive and repetitive behaviors. Symptoms of ASD likely emerge from a complex interaction between pre-existing neurodevelopmental vulnerabilities and the child's environment, modified by compensatory skills and protective factors. Prospective studies of infants at high familial risk for ASD (who have an older sibling with a diagnosis) are beginning to characterize these developmental pathways to the emergence of clinical symptoms. Here, we review the range of behavioral and neurocognitive markers for later ASD that have been identified in high-risk infants in the first years of life. We discuss theoretical implications of emerging patterns, and identify key directions for future work, including potential resolutions to several methodological challenges for the field. Mapping how ASD unfolds from birth is critical to our understanding of the developmental mechanisms underlying this disorder. A more nuanced understanding of developmental pathways to ASD will help us not only to identify children who need early intervention, but also to improve the range of interventions available to them.

Stability and plasticity of auditory brainstem function across the lifespan

The human auditory brainstem is thought to undergo rapid developmental changes early in life until age ∼2 followed by prolonged stability until aging-related changes emerge. However, earlier work on brainstem development was limited by sparse sampling across the lifespan and/or averaging across children and adults. Using a larger dataset than past investigations, we aimed to trace more subtle variations in auditory brainstem function that occur normally from infancy into the eighth decade of life. To do so, we recorded auditory brainstem responses (ABRs) to a click stimulus and a speech syllable (da) in 586 normal-hearing healthy individuals. Although each set of ABR measures (latency, frequency encoding, response consistency, nonstimulus activity) has a distinct developmental profile, across all measures developmental changes were found to continue well past age 2. In addition to an elongated developmental trajectory and evidence for multiple auditory developmental processes, we revealed a period of overshoot during childhood (5-11 years old) for latency and amplitude measures, when the latencies are earlier and the amplitudes are greater than the adult value. Our data also provide insight into the capacity for experience-dependent auditory plasticity at different stages in life and underscore the importance of using age-specific norms in clinical and experimental applications.

Proposed toxic and hypoxic impairment of a brainstem locus in autism

Electrophysiological findings implicate site-specific impairment of the nucleus tractus solitarius (NTS) in autism. This invites hypothetical consideration of a large role for this small brainstem structure as the basis for seemingly disjointed behavioral and somatic features of autism. The NTS is the brain's point of entry for visceral afference, its relay for vagal reflexes, and its integration center for autonomic control of circulatory, immunological, gastrointestinal, and laryngeal function. The NTS facilitates normal cerebrovascular perfusion, and is the seminal point for an ascending noradrenergic system that modulates many complex behaviors. Microvascular configuration predisposes the NTS to focal hypoxia. A subregion--the "pNTS"--permits exposure to all blood-borne neurotoxins, including those that do not readily transit the blood-brain barrier. Impairment of acetylcholinesterase (mercury and cadmium cations, nitrates/nitrites, organophosphates, monosodium glutamate), competition for hemoglobin (carbon monoxide, nitrates/nitrites), and higher blood viscosity (net systemic oxidative stress) are suggested to potentiate microcirculatory insufficiency of the NTS, and thus autism.