Brief report: atypical neuromagnetic responses to illusory auditory pitch in children with autism spectrum disorders

Neural correlates of concurrent sound perception: A review and guidelines for future research

The perception of concurrent sound sources depends on processes (i.e., auditory scene analysis) that fuse and segregate acoustic features according to harmonic relations, temporal coherence, and binaural cues (encompass dichotic pitch, location difference, simulated echo). The object-related negativity (ORN) and P400 are electrophysiological indices of concurrent sound perception. Here, we review the different paradigms used to study concurrent sound perception and the brain responses obtained from these paradigms. Recommendations regarding the design and recording parameters of the ORN and P400 are made, and their clinical applications in assessing central auditory processing ability in different populations are discussed.

Atypical Bilateral Brain Synchronization in the Early Stage of Human Voice Auditory Processing in Young Children with Autism

Autism spectrum disorder (ASD) has been postulated to involve impaired neuronal cooperation in large-scale neural networks, including cortico-cortical interhemispheric circuitry. In the context of ASD, alterations in both peripheral and central auditory processes have also attracted a great deal of interest because these changes appear to represent pathophysiological processes; therefore, many prior studies have focused on atypical auditory responses in ASD. The auditory evoked field (AEF), recorded by magnetoencephalography, and the synchronization of these processes between right and left hemispheres was recently suggested to reflect various cognitive abilities in children. However, to date, no previous study has focused on AEF synchronization in ASD subjects. To assess global coordination across spatially distributed brain regions, the analysis of Omega complexity from multichannel neurophysiological data was proposed. Using Omega complexity analysis, we investigated the global coordination of AEFs in 3–8-year-old typically developing (TD) children (n = 50) and children with ASD (n = 50) in 50-ms time-windows. Children with ASD displayed significantly higher Omega complexities compared with TD children in the time-window of 0–50 ms, suggesting lower whole brain synchronization in the early stage of the P1m component. When we analyzed the left and right hemispheres separately, no significant differences in any time-windows were observed. These results suggest lower right-left hemispheric synchronization in children with ASD compared with TD children. Our study provides new evidence of aberrant neural synchronization in young children with ASD by investigating auditory evoked neural responses to the human voice.

Magnetoencephalography in the study of children with autism spectrum disorder

Magnetoencephalography (MEG) is a non-invasive neuroimaging technique that provides a measure of cortical neural activity on a millisecond timescale with high spatial resolution. MEG has been clinically applied to various neurological diseases, including epilepsy and cognitive dysfunction. In the past decade, MEG has also emerged as an important investigatory tool in neurodevelopmental studies. It is therefore an opportune time to review how MEG is able to contribute to the study of atypical brain development. We limit this review to autism spectrum disorder (ASD). The relevant published work for children was accessed using PubMed on 5 January 2015. Case reports, case series, and papers on epilepsy were excluded. Owing to their accurate separation of brain activity in the right and left hemispheres and the higher accuracy of source localization, MEG studies have added new information related to auditory-evoked brain responses to findings from previous electroencephalography studies of children with ASD. In addition, evidence of atypical brain connectivity in children with ASD has accumulated over the past decade. MEG is well suited for the study of neural activity with high time resolution even in young children. Although further studies are still necessary, the detailed findings provided by neuroimaging methods may aid clinical diagnosis and even contribute to the refinement of diagnostic categories for neurodevelopmental disorders in the future.

Case study: auditory brain responses in a minimally verbal child with autism and cerebral palsy

An estimated 30% of individuals with autism spectrum disorders (ASD) remain minimally verbal into late childhood, but research on cognition and brain function in ASD focuses almost exclusively on those with good or only moderately impaired language. Here we present a case study investigating auditory processing of GM, a nonverbal child with ASD and cerebral palsy. At the age of 8 years, GM was tested using magnetoencephalography (MEG) whilst passively listening to speech sounds and complex tones. Where typically developing children and verbal autistic children all demonstrated similar brain responses to speech and nonspeech sounds, GM produced much stronger responses to nonspeech than speech, particularly in the 65-165 ms (M50/M100) time window post-stimulus onset. GM was retested aged 10 years using electroencephalography (EEG) whilst passively listening to pure tone stimuli. Consistent with her MEG response to complex tones, GM showed an unusually early and strong response to pure tones in her EEG responses. The consistency of the MEG and EEG data in this single case study demonstrate both the potential and the feasibility of these methods in the study of minimally verbal children with ASD. Further research is required to determine whether GM's atypical auditory responses are characteristic of other minimally verbal children with ASD or of other individuals with cerebral palsy.

Enhanced segregation of concurrent sounds with similar spectral uncertainties in individuals with autism spectrum disorder

When acoustic signals from different sound sources are mixed upon arrival at the ears, the auditory system organizes these acoustic elements by their features. This study shows that individuals with autism spectrum disorder (ASD) performed better in terms of hearing a target sequence among distractors that had similar spectral uncertainties. Their superior performance in this task indicates an enhanced discrimination between auditory streams with the same spectral uncertainties but different spectro-temporal details. The enhanced discrimination of acoustic components may be related to the absence of the automatic grouping of acoustic components with the same features, which results in difficulties in speech perception in a noisy environment. On the other hand, the ASD group and the control group had similar performance in hearing a target sequence among distractors that had different spatial cues defined by interaural intensity differences.

Newborn Infants Detect Cues of Concurrent Sound Segregation

Separating concurrent sounds is fundamental for a veridical perception of one's auditory surroundings. Sound components that are harmonically related and start at the same time are usually grouped into a common perceptual object, whereas components that are not in harmonic relation or have different onset times are more likely to be perceived in terms of separate objects. Here we tested whether neonates are able to pick up the cues supporting this sound organization principle. We presented newborn infants with a series of complex tones with their harmonics in tune (creating the percept of a unitary sound object) and with manipulated variants, which gave the impression of two concurrently active sound sources. The manipulated variant had either one mistuned partial (single-cue condition) or the onset of this mistuned partial was also delayed (double-cue condition). Tuned and manipulated sounds were presented in random order with equal probabilities. Recording the neonates' electroencephalographic responses allowed us to evaluate their processing of the sounds. Results show that, in both conditions, mistuned sounds elicited a negative displacement of the event-related potential (ERP) relative to tuned sounds from 360 to 400 ms after sound onset. The mistuning-related ERP component resembles the object-related negativity (ORN) component in adults, which is associated with concurrent sound segregation. Delayed onset additionally led to a negative displacement from 160 to 200 ms, which was probably more related to the physical parameters of the sounds than to their perceptual segregation. The elicitation of an ORN-like response in newborn infants suggests that neonates possess the basic capabilities of segregating concurrent sounds by detecting inharmonic relations between the co-occurring sounds.

Neurophysiological findings from magnetoencephalography in autism spectrum disorder: a comprehensive review

ABSTRACT: 

Autism spectrum disorder (ASD) is an etiologically and clinically heterogeneous group of neurodevelopmental disorders, diagnosed exclusively by the behavioral phenotype. The neural basis of altered social, communicative, somatosensory, and restricted and repetitive behaviors remains largely unknown. Magnetoencephalography (MEG) provides a vital method of inquiry to identify the neurophysiological mechanisms of ASD, better illuminate etiologically distinct subgroups, understand the developmental trajectories of aberrant connectivity and track outcome. MEG is a neuroimaging methodology that can localize sources of electrical activity within the brain with millisecond resolution by noninvasively measuring the magnetic fields arising from such activity. This review addresses the central MEG findings exploring auditory, visual and somatosensory processing, higher-order/executive functioning, and resting state in individuals with ASD over the past decade and a half. We offer a summary of emerging trends related to neurophysiological alterations, aberrant hemispheric specialization and connectivity, as well as limitations in the literature and recommendations for future MEG investigations.

Reduced object related negativity response indicates impaired auditory scene analysis in adults with autistic spectrum disorder

Auditory Scene Analysis provides a useful framework for understanding atypical auditory perception in autism. Specifically, a failure to segregate the incoming acoustic energy into distinct auditory objects might explain the aversive reaction autistic individuals have to certain auditory stimuli or environments. Previous research with non-autistic participants has demonstrated the presence of an Object Related Negativity (ORN) in the auditory event related potential that indexes pre-attentive processes associated with auditory scene analysis. Also evident is a later P400 component that is attention dependent and thought to be related to decision-making about auditory objects. We sought to determine whether there are differences between individuals with and without autism in the levels of processing indexed by these components. Electroencephalography (EEG) was used to measure brain responses from a group of 16 autistic adults, and 16 age- and verbal-IQ-matched typically-developing adults. Auditory responses were elicited using lateralized dichotic pitch stimuli in which inter-aural timing differences create the illusory perception of a pitch that is spatially separated from a carrier noise stimulus. As in previous studies, control participants produced an ORN in response to the pitch stimuli. However, this component was significantly reduced in the participants with autism. In contrast, processing differences were not observed between the groups at the attention-dependent level (P400). These findings suggest that autistic individuals have difficulty segregating auditory stimuli into distinct auditory objects, and that this difficulty arises at an early pre-attentive level of processing.