Date of Award

1-24-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Communication Sciences and Disorders

Advisor(s)

Beth Prieve

Abstract

Purpose: Understanding the contributions of neural variability, measured by trial-to-trial fluctuations in an evoked neural response, to behavior has been particularly interesting to researchers since recent findings suggest that decreased cortical neural stability correlates with heightened autistic traits. This correlation has led some researchers to hypothesize a causal link between increased neural variability and heightened autistic traits and sensory sensitivities. Notably, these cortical findings are in response to multisensory stimuli, including auditory stimuli. In the brainstem, elevated neural variability evoked from monaurally presented auditory stimuli is associated with poorer syntactic performance, and some, albeit not all, studies have found group differences when comparing neural variability between autistic and nonautistic individuals. Yet, the potential relationship between neural variability in the brainstem and autistic traits and sensory sensitivities remains unexplored. The current study sought to elucidate (1) whether the neural variability observed in auditory brainstem responses (ABRs) elicited by click and synthetic 40ms /da/ stimuli differed depending on when analyzed post-stimulus onset and by stimulus type, (2) if neural variability was significantly related to sensory sensitivities evaluated through the parent-report Sensory Profile (SP) survey (3) and whether neural variability predicted the spectrum of parent-reported autistic traits, quantified using the Autism Quotient (AQ) and the Social Responsiveness Scale, Second Edition (SRS-2) among a combined group of nonautistic and autistic school-age children. Methods: Forty-four children, including 18 autistic and 26 nonautistic peers aged 6-16.9 years, participated. Before electrophysiological recording, participants underwent a routine hearing evaluation and an IQ assessment using the Wechsler Abbreviated Scale of Intelligence, Second Edition (WASI-II). Parent(s)/caregivers completed the SP, AQ, and SRS-2. The ABRs were evoked by binaural presentation of clicks and a 40 ms synthetic /da/ stimulus and recorded ipsilaterally using a two-channel montage via scalp electrodes. Two waveforms, each comprised of 3000 sweeps, were correlated together for the entire click response (1-8 ms) and the various response components of the sABR: the complete response (0-55 ms), the onset (5-10 ms), the frequency-following (22-40 ms), and the offset (45-50 ms) responses. A repeated measures of analysis of variance was conducted to determine if the degree of neural variability differed by response components. Multiple linear regression models were constructed and tested to determine if neural variability was a significant predictor of sensory sensitivities or autistic traits. Results: Significant differences in neural variability were found among the response components analyzed. Neural variability in the onset sABR and click ABR were not significantly different, aligning with existing literature suggesting the two response components are analogous. No meaningful predictive relationships emerged between neural variability and sensory sensitivities. In contrast, neural variability of the sABR offset response and entire click ABR predicted autistic traits after controlling for verbal IQ. Specifically, increased neural variability was associated with heightened total scores on AQ and SRS-2. Conclusions: The study challenges current methods by highlighting the relevance of analyzing different response components within the sABR, instead of only the FFR, and advocates for a paradigm shift from case-control studies toward individualized predictive modeling studies, especially in heterogeneous conditions like autism. Although neural variability within the auditory brainstem pathway did not predict sensory sensitivities, it emerged as a predictor of autistic traits. By further understanding neural variability's complex relationship with behavioral traits, researchers may be able to facilitate a more comprehensive understanding of individual differences in auditory processing and autistic traits.

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