Brainstem transcription of speech is disrupted in children with autism spectrum disorders - PubMed (original) (raw)

Brainstem transcription of speech is disrupted in children with autism spectrum disorders

Nicole Russo et al. Dev Sci. 2009 Jul.

Abstract

Language impairment is a hallmark of autism spectrum disorders (ASD). The origin of the deficit is poorly understood although deficiencies in auditory processing have been detected in both perception and cortical encoding of speech sounds. Little is known about the processing and transcription of speech sounds at earlier (brainstem) levels or about how background noise may impact this transcription process. Unlike cortical encoding of sounds, brainstem representation preserves stimulus features with a degree of fidelity that enables a direct link between acoustic components of the speech syllable (e.g. onsets) to specific aspects of neural encoding (e.g. waves V and A). We measured brainstem responses to the syllable /da/, in quiet and background noise, in children with and without ASD. Children with ASD exhibited deficits in both the neural synchrony (timing) and phase locking (frequency encoding) of speech sounds, despite normal click-evoked brainstem responses. They also exhibited reduced magnitude and fidelity of speech-evoked responses and inordinate degradation of responses by background noise in comparison to typically developing controls. Neural synchrony in noise was significantly related to measures of core and receptive language ability. These data support the idea that abnormalities in the brainstem processing of speech contribute to the language impairment in ASD. Because it is both passively elicited and malleable, the speech-evoked brainstem response may serve as a clinical tool to assess auditory processing as well as the effects of auditory training in the ASD population.

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Figures

Figure 1

Figure 1. Speech stimulus /da/ and TD grand average response in quiet and background noise conditions

The /da/ has an onset burst followed by a transition to the periodic vowel portion. The stimulus waveform is shifted ∼7 ms to compensate for neural lag in the response. Brainstem responses to /da/ were robust in quiet, reflecting stimulus features with great precision. Waves V and A reflect the onset of the /da/ stimulus, wave C represents the transition to the periodic portion, waves D, E, and F comprise the frequency-following response, and wave O signals the offset of the response. The wavelengths between waves D-E and E-F correspond to the fundamental frequency (F0, pitch) of the stimulus, while F1 and higher frequency components are encoded in the smaller peaks between the dominant F0 waves. In background noise (dashed line), many of the transient response peaks are abolished, while sustained activity (frequency-following response) and waves F and O persisted.

Figure 2

Figure 2. Comparison of grand average onset responses to /da/ in quiet in TD children (n=18; black line) and children with ASD (n=21; gray line)

The neural response to the onset of speech sounds was less synchronous in children with ASD (gray) as compared to TD children (black). Notably the onset response in children with ASD showed significant delays in waves V and A, and also a longer interpeak interval (horizontal arrow).

Figure 3

Figure 3. Comparison of grand average frequency-following responses to /da/ in quiet in TD children (black line) and children with ASD (gray line)

The frequency-following response in children with ASD showed significant delays in peaks D and F; peak F was also reduced in amplitude, demonstrating reduced phase locking in brainstems of children with ASD.

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