Electrophysiological response during auditory gap detection: Biomarker for sensory and communication alterations in autism spectrum disorder?

Neurophysiological measures of auditory sensory processing are associated with adaptive behavior in children with Autism Spectrum Disorder

BACKGROUND

Atypical auditory cortical processing is consistently found in scalp electrophysiological and magnetoencephalographic studies of Autism Spectrum Disorder (ASD), and may provide a marker of neuropathological brain development. However, the relationship between atypical cortical processing of auditory information and adaptive behavior in ASD is not yet well understood.

METHODS

We sought to test the hypothesis that early (100-175 ms) auditory processing in ASD is related to everyday adaptive behavior through the examination of auditory event-related potentials (AEPs) in response to simple tones and Vineland Adaptive Behavior Scales in a large cohort of children with ASD (N = 84), aged 6-17, and in age- and IQ- matched neurotypically (NT) developing controls (N = 132).

RESULTS

Statistical analyses revealed significant group differences in early AEPs over temporal scalp regions (150-175 ms), and the expected rightward lateralization of the AEP (100-125 ms and 150-175 ms) to tonal stimuli in both groups. Lateralization of the AEP (150-175 ms) was significantly associated with adaptive functioning in the socialization domain.

CONCLUSIONS

These results lend support to the hypothesis that atypical processing of sensory information is related to everyday adaptive behavior in autism.

Autism Spectrum Disorder and auditory sensory alterations: a systematic review on the integrity of cognitive and neuronal functions related to auditory processing

Autism Spectrum Disorder (ASD) is a neurodevelopmental condition with a wide spectrum of symptoms, mainly characterized by social, communication, and cognitive impairments. Latest diagnostic criteria according to DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, 2013) now include sensory issues among the four restricted/repetitive behavior features defined as "hyper- or hypo-reactivity to sensory input or unusual interest in sensory aspects of environment". Here, we review auditory sensory alterations in patients with ASD. Considering the updated diagnostic criteria for ASD, we examined research evidence (2015-2022) of the integrity of the cognitive function in auditory-related tasks, the integrity of the peripheral auditory system, and the integrity of the central nervous system in patients diagnosed with ASD. Taking into account the different approaches and experimental study designs, we reappraise the knowledge on auditory sensory alterations and reflect on how these might be linked with behavior symptomatology in ASD.

Speech Processing in Autism Spectrum Disorder: An Integrative Review of Auditory Neurophysiology Findings

Purpose Investigations into the nature of communication disorders in autistic individuals increasingly evaluate neural responses to speech stimuli. This integrative review aimed to consolidate the available data related to speech and language processing across levels of stimulus complexity (from single speech sounds to sentences) and to relate it to the current theories of autism. Method An electronic database search identified peer-reviewed articles using event-related potentials or magnetoencephalography to investigate auditory processing from single speech sounds to sentences in autistic children and adults varying in language and cognitive abilities. Results Atypical neural responses in autistic persons became more prominent with increasing stimulus and task complexity. Compared with their typically developing peers, autistic individuals demonstrated mostly intact sensory responses to single speech sounds, diminished spontaneous attentional orienting to spoken stimuli, specific difficulties with categorical speech sound discrimination, and reduced processing of semantic content. Atypical neural responses were more often observed in younger autistic participants and in those with concomitant language disorders. Conclusions The observed differences in neural responses to speech stimuli suggest that communication difficulties in autistic individuals are more consistent with the reduced social interest than the auditory dysfunction explanation. Current limitations and future directions for research are also discussed.

Integral perception, but separate processing: The perceptual normalization of lexical tones and vowels

In tonal languages, speech variability arises in both lexical tone (i.e., suprasegmentally) and vowel quality (segmentally). Listeners can use surrounding speech context to overcome variability in both speech cues, a process known as extrinsic normalization. Although vowels are the main carriers of tones, it is still unknown whether the combined percept (lexical tone and vowel quality) is normalized integrally or in partly separate processes. Here we used electroencephalography (EEG) to investigate the time course of lexical tone normalization and vowel normalization to answer this question. Cantonese adults listened to synthesized three-syllable stimuli in which the identity of a target syllable - ambiguous between high vs. mid-tone (Tone condition) or between /o/ vs. /u/ (Vowel condition) - was dependent on either the tone range (Tone condition) or the formant range (Vowel condition) of the first two syllables. It was observed that the ambiguous tone was more often interpreted as a high-level tone when the context had a relatively low pitch than when it had a high pitch (Tone condition). Similarly, the ambiguous vowel was more often interpreted as /o/ when the context had a relatively low formant range than when it had a relatively high formant range (Vowel condition). These findings show the typical pattern of extrinsic tone and vowel normalization. Importantly, the EEG results of participants showing the contrastive normalization effect demonstrated that the effects of vowel normalization could already be observed within the N2 time window (190-350 ms), while the first reliable effect of lexical tone normalization on cortical processing was observable only from the P3 time window (220-500 ms) onwards. The ERP patterns demonstrate that the contrastive perceptual normalization of lexical tones and that of vowels occur at least in partially separate time windows. This suggests that the extrinsic normalization can operate at the level of phonemes and tonemes separately instead of operating on the whole syllable at once.

Autonomic and Electrophysiological Evidence for Reduced Auditory Habituation in Autism

It is estimated that nearly 90% of children on the autism spectrum exhibit sensory atypicalities. What aspects of sensory processing are affected in autism? Although sensory processing can be studied along multiple dimensions, two of the most basic ones involve examining instantaneous sensory responses and how the responses change over time. These correspond to the dimensions of 'sensitivity' and 'habituation'. Results thus far have indicated that autistic individuals do not differ systematically from controls in sensory acuity/sensitivity. However, data from studies of habituation have been equivocal. We have studied habituation in autism using two measures: galvanic skin response (GSR) and magneto-encephalography (MEG). We report data from two independent studies. The first study, was conducted with 13 autistic and 13 age-matched neurotypical young adults and used GSR to assess response to an extended metronomic sequence. The second study involved 24 participants (12 with an ASD diagnosis), different from those in study 1, spanning the pre-adolescent to young adult age range, and used MEG. Both studies reveal consistent patterns of reduced habituation in autistic participants. These results suggest that autism, through mechanisms that are yet to be elucidated, compromises a fundamental aspect of sensory processing, at least in the auditory domain. We discuss the implications for understanding sensory hypersensitivities, a hallmark phenotypic feature of autism, recently proposed theoretical accounts, and potential relevance for early detection of risk for autism.

Atypical processing of tones and phonemes in Rett Syndrome as biomarkers of disease progression

Due to severe motor impairments and the lack of expressive language abilities seen in most patients with Rett Syndrome (RTT), it has proven extremely difficult to obtain accurate measures of auditory processing capabilities in this population. Here, we examined early auditory cortical processing of pure tones and more complex phonemes in females with Rett Syndrome (RTT), by recording high-density auditory evoked potentials (AEP), which allow for objective evaluation of the timing and severity of processing deficits along the auditory processing hierarchy. We compared AEPs of 12 females with RTT to those of 21 typically developing (TD) peers aged 4-21 years, interrogating the first four major components of the AEP (P1: 60-90 ms; N1: 100-130 ms; P2: 135-165 ms; and N2: 245-275 ms). Atypicalities were evident in RTT at the initial stage of processing. Whereas the P1 showed increased amplitude to phonemic inputs relative to tones in TD participants, this modulation by stimulus complexity was absent in RTT. Interestingly, the subsequent N1 did not differ between groups, whereas the following P2 was hugely diminished in RTT, regardless of stimulus complexity. The N2 was similarly smaller in RTT and did not differ as a function of stimulus type. The P2 effect was remarkably robust in differentiating between groups with near perfect separation between the two groups despite the wide age range of our samples. Given this robustness, along with the observation that P2 amplitude was significantly associated with RTT symptom severity, the P2 has the potential to serve as a monitoring, treatment response, or even surrogate endpoint biomarker. Compellingly, the reduction of P2 in patients with RTT mimics findings in animal models of RTT, providing a translational bridge between pre-clinical and human research.

Test-retest reliability of the N2 event-related potential in school-aged children with autism spectrum disorder (ASD)

OBJECTIVE

The N2 ERP component is used as a biomeasure of executive function in children with autism spectrum disorder (ASD). The aim of the current study was to evaluate the test-retest reliability of N2 amplitude in this population.

METHODS

ERPs were recorded from 7 to 11-year-old children with ASD during Flanker (n = 21) and Go/Nogo tasks (n = 14) administered at two time points separated by approximately three months. Reliability of the N2 component was examined using intraclass correlation coefficients (ICCs).

RESULTS

Reliability for mean N2 amplitude obtained during the Flanker task was moderate (congruent: ICC = 0.542, 95% CI [0.173, 0.782]; incongruent: ICC = 0.629, 95% CI [0.276, 0.831]). Similarly, reliability for the Go/Nogo task ranged from moderate to good ('go': ICC = 0.817, 95% CI [0.535, 0.937]; 'nogo': ICC = 0.578, 95% CI [0.075, 0.843]).

CONCLUSIONS

These findings support the use of N2 amplitude as a biomeasure of executive function in school-aged children with ASD.

SIGNIFICANCE

This research addresses a critical gap in clinical neurophysiology, as an understanding of the stability and reliability of the N2 component is needed in order to differentiate variance explained by repeated measurement versus targeted treatments and interventions.