Abstract
Prevailing theories of the neural basis of at least a subset of individuals with autism spectrum disorder (ASD) include an imbalance of excitatory and inhibitory neurotransmission. These circuitry imbalances are commonly probed in adults using auditory steady-state responses (ASSR, driven at 40 Hz) to elicit coherent electrophysiological responses (EEG/MEG) from intact circuitry. Challenges to the ASSR methodology occur during development, where the optimal ASSR driving frequency may be unknown. An alternative approach (more agnostic to driving frequency) is the amplitude-modulated (AM) sweep in which the amplitude of a tone (with carrier frequency 500 Hz) is modulated as a sweep from 10 to 100 Hz over the course of ∼15 s. Phase synchrony of evoked responses, measured via intra-trial coherence, is recorded (by EEG or MEG) as a function of frequency. We applied such AM sweep stimuli bilaterally to 40 typically developing and 80 children with ASD, aged 6–18 years. Diagnoses were confirmed by DSM-5 criteria as well as autism diagnostic observation schedule (ADOS) observational assessment. Stimuli were presented binaurally during MEG recording and consisted of 20 AM swept stimuli (500 Hz carrier; sweep 10–100 Hz up and down) with a duration of ∼30 s each. Peak intra-trial coherence values and peak response frequencies of source modeled responses (auditory cortex) were examined. First, the phase synchrony or inter-trial coherence (ITC) of the ASSR is diminished in ASD; second, hemispheric bias in the ASSR, observed in typical development (TD), is maintained in ASD, and third, that the frequency at which the peak response is obtained varies on an individual basis, in part dependent on age, and with altered developmental trajectories in ASD vs. TD. Finally, there appears an association between auditory steady-state phase synchrony (taken as a proxy of neuronal circuitry integrity) and clinical assessment of language ability/impairment. We concluded that (1) the AM sweep stimulus provides a mechanism for probing ASSR in an unbiased fashion, during developmental maturation of peak response frequency, (2) peak frequencies vary, in part due to developmental age, and importantly, (3) ITC at this peak frequency is diminished in ASD, with the degree of ITC disturbance related to clinically assessed language impairment.
Highlights
Gamma-band (30–80 Hz) electrophysiological activity elicited from sensory cortices may provide a window into the maturity and viability of local neuronal circuitry
Given the high degree of heterogeneity in the language abilities of children diagnosed with ASD and the putative relationship between the auditory steadystate response (ASSR) and auditory cortex function, we examined the relationship between peak ASSR inter-trial coherence (ITC) value and a behavioral/clinical language ability index: the CLSS of the CELF
The main finding of this study is that auditory gammaband responses, especially in terms of phase synchrony (ITC), are diminished in ASD compared with age-matched
Summary
Gamma-band (30–80 Hz) electrophysiological activity elicited from sensory cortices may provide a window into the maturity and viability of local neuronal circuitry. This in turn may be reflective of the balance between excitatory and inhibitory neuronal activity and, as such, the balance of excitatory and inhibitory neurotransmitters ( glutamate and GABA). Eliciting gamma-band activity can be achieved through a variety of stimulation paradigms. The most prevalent paradigm for auditory cortex gamma activity is the auditory steadystate response (ASSR). Studies in adults have suggested that the ASSR is largest in response to presentations in the gamma range at 40 Hz (Galambos et al, 1981; Picton et al, 2003). While the 40 Hz ASSR has been used to illustrate consistent gamma abnormalities in several neurodevelopmental disorders, principally schizophrenia (Brenner et al, 2003; Hong et al, 2004; Light et al, 2006; Hamm et al, 2011; Lenz et al, 2011; Edgar et al, 2014), studies focused on ASD have been more inconsistent (Rojas et al, 2006; Wilson et al, 2007; Edgar et al, 2016; Ono et al, 2020; Seymour et al, 2020; Stroganova et al, 2020)
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