Differential Altered Auditory Event-Related Potential Responses in Young Boys on the Autism Spectrum With and Without Disproportionate Megalencephaly.
Big-headed autism toddlers give bigger brain waves to loud sounds, marking a biologically distinct subgroup.
01Research in Context
What this study did
De Meo-Monteil et al. (2019) wired up three groups of little boys.
One group had autism and very big heads. One had autism and normal heads. One group had no autism.
The team played sudden loud beeps while the boys sat still. They measured tiny brain waves that happen in the first second after each sound.
What they found
The big-headed autism group showed a unique wave shape. Their brains reacted faster and stronger to the loud sounds.
The other two groups looked almost the same. The finding hints that big-brain autism is a separate biology.
How this fits with other research
Amaral et al. (2017) counted heads first. They showed that fifteen out of every hundred boys with autism have megalencephaly and worse daily skills. Rosanna’s work adds a brain-wave marker to that head-size clue.
Chuah et al. (2025) pooled many MMN studies. They saw smaller change-detection waves in autism, but linked to daily living skills, not head size. The loud-sound wave Rosanna used is different from MMN, so the two results sit side-by-side, not in conflict.
Yoshimura et al. (2016) tracked younger babies and saw odd P1m growth curves. Rosanna’s toddlers extend that story: by age two, head size splits the autism crowd into clear electrical types.
Why it matters
You can’t run EEG on every client, but you can track head growth with a tape measure. When a toddler’s head vaults above the curve and language stalls, think "biological subtype." Expect slower progress, plan more intense early intervention, and prepare families for a longer haul. The loud-sound wave is a research tool today; head size is your clinic tool right now.
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02At a glance
03Original abstract
Autism spectrum disorder (ASD), characterized by impairments in social communication and repetitive behaviors, often includes altered responses to sensory inputs as part of its phenotype. The neurobiological basis for altered sensory processing is not well understood. The UC Davis Medical Investigation of Neurodevelopmental Disorders Institute Autism Phenome Project is a longitudinal, multidisciplinary study of young children with ASD and age-matched typically developing (TD) controls. Previous analyses of the magnetic resonance imaging data from this cohort have shown that ∼15% of boys with ASD have disproportionate megalencephaly (DM) or brain size to height ratio, that is 1.5 standard deviations above the TD mean. Here, we investigated electrophysiological responses to auditory stimuli of increasing intensity (50-80 dB) in young toddlers (27-48 months old). Analyses included data from 36 age-matched boys, of which 24 were diagnosed with ASD (12 with and 12 without DM; ASD-DM and ASD-N) and 12 TD controls. We found that the two ASD subgroups differed in their electrophysiological response patterns to sounds of increasing intensity. At early latencies (55-115 ms), ASD-N does not show a loudness-dependent response like TD and ASD-DM, but tends to group intensities by soft vs. loud sounds, suggesting differences in sensory sensitivity in this group. At later latencies (145-195 ms), only the ASD-DM group shows significantly higher amplitudes for loud sounds. Because no similar effects were found in ASD-N and TD groups, this may be related to their altered neuroanatomy. These results contribute to the effort to delineate ASD subgroups and further characterize physiological responses associated with observable phenotypes. Autism Res 2019, 12: 1236-1250. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Approximately 15% of boys with ASD have much bigger brains when compared to individuals with typical development. By recording brain waves (electroencephalography) we compared how autistic children, with or without big brains, react to sounds compared to typically developing controls. We found that brain responses in the big-brained group are different from the two other groups, suggesting that they represent a specific autism subgroup.
Autism research : official journal of the International Society for Autism Research, 2019 · doi:10.1002/aur152