Neurophysiological Evaluation of Acoustic Startle Response in Japanese Children with Autism Spectrum Disorders

Background: Acoustic startle modulation, including prepulse inhibition (PPI), is considered to be one of the most promising neurophysiological index for translational research in psychiatry. However, as for autistic spectrum disorders (ASD), startle modulation was not consistent through children to adults: adults with ASD presented PPI impairment, on the other hand, children with ASD did not. Above all, basic ASR profile of ASD is not known well. People with ASD is known to have enhanced auditory perception, however, ASR to weak stimuli in ASD is not investigated well. Recently, children with ASD are reported to have prolonged startle latency. And, in addition, basic ASR profile, such as startle magnitude, is known to differ across races. Thus, basic ASR profile, including startle maginitude, especially to weak stimuli, and startle latency, should be investigated across races.

Objectives: To evaluate the basic ASR profile, including peak startle latency, startle maginitude to weaker stimuli, in Japanese children with ASD and typical development (TD), and, to evaluate their relationship to ASD characteristics

Methods: Ten Japanese children with ASD and 34 Japanese children with TD participated in this study. The electromyographic activity of the left orbicularis oculi muscle to acoustic stimuli of 65 to 115 dB SPL, in increments of 5 dB, was measured to evaluate ASR. Average eyeblink magnitude, average peak startle latency of ASR for each acoustic stimuli intensity was evaluated. The Electroencephalography (EEG) was also recorded during the testing. Based on the electric potential distribution of ERP waveform, the exact low resolution brain electromagnetic tomography (eLORETA) software was used to compute the cortical three-dimensional distribution of electric neuronal activity, current density. ASD characteristics of all subjects were assessed by Social Responsive Scale (SRS).

Results: Compared to TD, ASD group showed significantly larger startle magnitude to weak acoustic stimuli of 65, 70, and 80 dB. Peak startle latency was prolonged in children with ASD compared to TD. Startle magnitude to weak acoustic stimuli of 65dB, 70dB, 75dB, and, 80dB correlated negatively to T score of SRS Social Awareness subscale. Peak startle latency correlated with T score of SRS total score and SRS subscale of Social Awareness, Social Cognition, Social Communication, and, Autistic Mannerisms. EEG current source density was widely distributed across brain areas in TD, however, was restricted mostly in frontal region in ASD.

Conclusions: Larger startle magnitude to weak stimuli and prolonged peak startle latency were related to several aspects of ASD characteristics. Brain activity involved in the mechanism of ASR was atypical in ASD. Our results suggest that comprehensive investigation of ASR, including startle magnitude to weak stimuli, peak startle latency, might contribute to uncover the impairment of the neural circuitry in autism.