Date on Master's Thesis/Doctoral Dissertation

7-2014

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Bioengineering

Committee Chair

El-Baz, Ayman Sabry

Author's Keywords

Autism; EEG; Gamma coherence; Autonomic function; Repetitive transcranial magnetic stimulation (rTMS)

Subject

Autism--Treatment; Autonomic nervous system

Abstract

INTRODUCTION: Autism spectrum disorder (ASD) is a developmental disorder that is characterized by difficulty in social interactions, limited range of interests, and repetitive behaviors. ASD has been shown to negatively affect both ambient vision and the autonomic nervous system (ANS). The objectives of this thesis were to determine the efficacy of two novel therapies, visuo-motor training with ambient prism lenses and repetitive transcranial magnetic stimulation (rTMS), on autonomic balance and EEG gamma coherence. Heart rate variability (HRV) and skin conductance level (SCL) were used as indicators of autonomic function. HRV is an excellent indicator of autonomic balance because it has a low frequency (LF) component, representative of combined parasympathetic and sympathetic inputs, and a high frequency (HF) component, representative of parasympathetic only inputs. SCL is controlled solely by sympathetic inputs and is therefore indicative of sympathetic tone. Gamma coherence refers to the coactivation of different regions of the brain during completion of a task. DATA COLLECTION: Autonomic measures of heart rate (HR) and SCL were collected for both the prism lens study and the rTMS study. Patients enrolled in the prism lens study were fitted with an appropriate pair of lenses and performed daily visuo-motor exercises for six months. Autonomic data was collected twice: once at the baseline (before treatment) and again after completing the prism lens training course. Patients enrolled in the rTMS study underwent 18 weekly sessions of TMS. Autonomic data was collected during each session. EEG data was collected twice for both the prism lens and rTMS study, once before and after the course of therapy. Behavioral checklists such as the Aberrant Behavior Checklist (ABC) and the Repetitive Behavior Checklist (RBS) were completed by the subjects’ parents before and after therapy. DATA PROCESSING AND ANALYSIS: HR and SCL data collected as the patients watched scenes from The Lion King (prism lens study) or as patients received TMS (rTMS study) was exported into Microsoft Excel to begin pre-processing. Statistical analyses were performed using SPSS 14.0 software. HR data was further analyzed using Kubios HRV software to calculate heart rate variability (HRV) measures. EEG data was exported into a software program called Brain Electrical Source Analysis (BESA) for analysis of gamma coherence. RESULTS: Results from the prism lens study show that average HR among participants decreased significantly after completion of prism lens therapy. There was also a decrease in LF power, an increase in the percentage of HF power, a decrease in the ratio of LF to HF power (cardiac autonomic balance index), and a decrease in SCL. No significant changes were observed in gamma coherence following prism lens therapy. Results from the rTMS study show changes in several measures that reached significance: increased RR interval (time lapse between successive heartbeats), increased SDNN (standard deviation of RR interval), increased HF component of HRV, decreased LF/HF ratio, and decreased SCL. In addition, there was increased gamma coherence between frontal-temporal regions and frontal-parietal regions following TMS therapy. CONCLUSIONS: ASD has been shown to present symptoms of disrupted autonomic balance resulting from excess activity of the sympathetic branch and suppressed parasympathetic activity. In this thesis, autonomic balance, as indicated by HRV and SCL, was used as a measure of the effectiveness of two novel therapies for the treatment of ASD: prism lenses and rTMS. Both therapies resulted in an improvement of autonomic balance through the activation of the parasympathetic branch and/or by reducing activity of the sympathetic branch. Prism lens therapy did not improve gamma coherence; however, TMS therapy was shown to increase gamma coherence between frontal-parietal and frontal-temporal regions during processing target stimuli.

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