Background: Rett syndrome (RS) is a rare neurodevelopmental disorder characterized by mutations in the MECP2 gene. Patients with RS have severe motor abnormalities and are often unable to walk, use hands and speak. The preservation of perceptual and cognitive functions is hard to assess, while clinicians and care-givers point out that these patients need more time to process information than typically developing peers. Neurophysiological correlates of auditory processing have been also found to be distorted in RS, but sound presentation rates were relatively quick in these studies (stimulus onset asynchrony, SOA < 1000 ms). As auditory event-related potential (ERP) is typically increased with prolongation of SOA we aim to study if SOA prolongation might compensate for observed abnormalities. Methods: We presented a repetitive stimulus (1000 Hz) at three different SOAs of 900 ms, 1800 ms, and 3600 ms in children with RS (N = 24, Mean age = 9.0 ± 3.1) and their typical development (TD) peers (N = 27, Mean age = 9.7 ± 3.4) while recording 28-channels electroencephalogram, EEG. Some RS participants (n = 10) did not show clear ERP and were excluded from the analysis. Results: Major ERP components (here assessed as N1P1 and P2N1 peak-to-peak values) were smaller at SOA 900 than at longer SOAs in both groups, pointing out that the basic mechanism of adaptation in the auditory system is preserved in at least in RS patients with evident ERPs. At the same time the latencies of these components were significantly delayed in the RS than in TD. Moreover, late components (P2N1 and N2P2) were drastically reduced in Rett syndrome irrespective of the SOA, suggesting a largely affected mechanism of integration of upcoming sensory input with memory. Moreover, developmental stagnation of auditory ERP characterized patients with RS: absence of typical P2N1 enlargement and P1 and N1 shortening with age at least for shortest SOA. Limitations: We could not figure out the cause for the high percentage of no-evident ERP RS participants and our final sample of the RS group was rather small. Also, our study did not include a control clinical group. Conclusions: Thus, auditory ERPs inform us about abnormalities within auditory processing that cannot be fully overcomed by slowing presentation rate.

In adults, the rate of stimuli presentation has been shown to play a critical role for the event related potentials (ERP): its components become larger as presentation rate decreases. But there are few works evaluating developmental changes of this ERP modulation that might provide insights into basic forms of learning. The current study aims to examine the developmental changes in the effect of the presentation rate on ERP. Participants (N = 48) of four age groups (2-7, 8-11, 12-17 and 18-35 years old) were presented with auditory tone (1000 Hz) at three different stimulus onset asynchrony (SOA): 0.9, 1.8, and 3.6 s. During stimuli presentation 28-channels electroencephalogram (EEG) was recorded. Amplitude of ERP components increased with SOA prolongation. However, this effect was differently pronounced in each of the age groups, depending on the component and cortical site. N1P1 amplitude was increased from 0.9 to 1.8 s SOA in two oldest groups (12-17 years old and adults) predominantly at fronto-central sites. Similar increase demonstrated P2N1 component but starting from younger group (8-11 years old). Only the adult group was characterized by a significant increase in N1P1 and P2N1 amplitudes with SOA increase from 1.8 to 3.6 s. Thus, the effect of presentation rate on ERP is not fully mature even at adolescence and depends on the component with P2N1 amplitude showing modulations at younger age.

Rett Syndrome (RS) is a rare neurodevelopmeтtal disorder characterized by mutations in theMECP2gene. Patients with RS have severe motor abnormalities and are often unable to walk, use hands and speak. The preservation of perceptual and cognitive functions is hard to assess, while clinicians and care-givers point out that these patients need more time to process information than typically developing peers. Here we examine neurophysiological correlates of auditory processing in RS as a function of presentation rate. From previous literature we knew that auditory event-related potential (ERP) is increased with prolongation of interstimulus interval (ISI). We presented a repetitive stimulus (1000Hz) at three different ISI of 900 ms, 1800 ms, and 3600 ms in children with RS and their typical development peers (TD) aged 2.5–16 years while recording 28-channels electroencephalogram, EEG. The amplitude of N1 and P2 components of event-related potential (ERP) was smaller at ISI 900 than at longer ISIs in both groups, pointing out that the basic mechanism of adaptation in the auditory system is preserved in Rett Syndrome. At the same time the latency of these components was significantly delayed in the RS than in TD. Moreover, late components (P2 and N2) were drastically reduced in Rett Syndrome irrespective of the ISI, suggesting a severely affected mechanism of integration of upcoming sensory input with memory. Based on these ERP measures it was possible to differentiate RS from TD with great accuracy (0.922 ± 0.047), being maximal with shortest ISI, supporting its implication as potential output measures in clinical trials as well as pointing to the diminishing of the neurophysiological differences between RS and TD with slowing down the presentation rate.

Background: Amplitude rise time is a critical acoustic cue for speech perception, yet its neurophysiological processing remains uninvestigated in autism spectrum disorder characterized by communication deficits, sensory abnormalities and often speech delay. This study examined whether children with autism spectrum disorder differ from typically developing peers in auditory event-related potential components across a continuum of rise times. Methods: Electroencephalography was recorded during passive presentation of pure tones with five rise time values (15, 30, 60, 120, 240 ms) in 42 children (21 with autism spectrum disorder, 21 typically developing, aged 4–10 years). Linear mixed models were used to analyze latencies and amplitudes of P1 and N2 components. Results: Children with autism spectrum disorder showed a less systematic pattern of neural modulation across rise times compared to typically developing peers. P1 amplitude was reduced at 15 and 60 ms (trend at 30 ms), with no significant group differences at longer rise times. N2 latency showed an atypical decrease at 60 ms compared to 30 ms, contrasting with the systematic increase observed in typically developing children. P1N2 amplitude reached a minimum at 60 ms in autism spectrum disorder, whereas typically developing children showed a gradual decrease across rise times. Conclusions: These findings provide the first evidence of atypical neurophysiological processing of rise time in children with autism spectrum disorder, with the most pronounced differences in the range of rapid acoustic onsets. Group differences were not detected at longer rise times, suggesting a selective rather than global deficit in temporal envelope processing.

Objectives: Amplitude rise time (RT) is a critical acoustic cue for speech perception, playing an important role in auditory processing of both speech and non-speech sounds. This study examined neurophysiological processing of RT in children with autism spectrum disorder (ASD) compared to typically developing (TD) peers. Methods: EEG was recorded during passive presentation of pure tones with five RT values (15, 30, 60, 120, 240 ms) in 42 children (ASD: n = 21, TD: n = 21, aged 4–10 years). Linear mixed models were used to analyze latencies and amplitudes of P1 and N2 components of event-related potential. Results: Children with ASD and TD peers showed distinct patterns of neural modulation across RTs. TD children show general increase in latency and decrease in amplitude of ERP components with increase in RT. While this pattern holds for P1 latency also for children with ASD, P1 amplitude was reduced in ASD compared to TD peers specifically at shorter rise times (15–60 ms), indicating weaker encoding of rapid acoustic onsets. For N2 latency children with ASD showed an atypical drop at 60 ms compared to 30 ms RT. P1N2 amplitude reached its minimum at 60 ms RT in ASD contrasting systematic decrease from 15 to 240 ms RT in TD. Conclusions: Together, these findings suggest that children with ASD show a less systematic pattern of neural modulation across the rise time continuum, particularly in the range of rapid acoustic onsets (15–60 ms), while processing of more gradual onsets remains relatively intact.