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Updated: Jul 7, 2026
Probing the Brain in Autism Using fMRI and Diffusion Tensor Imaging
Published on: September 12, 2011
Evidence of brain overgrowth in the first year of life in autism
Eric Courchesne1, Ruth Carper, Natacha Akshoomoff
1Department of Neuroscience, School of Medicine, University of California, San Diego, La Jolla, USA. ecourchesne@ucsd.edu
Insights
Autism spectrum disorder (ASD) is preceded by abnormal brain growth, starting with a smaller head size at birth and rapid head growth in infancy. This accelerated growth pattern may signal early risk for ASD.
Area of Science:
- Neuroscience
- Developmental Pediatrics
- Genetics
Background:
- Autism spectrum disorder (ASD) often becomes clinically apparent around 2-3 years of age, by which time significant brain overgrowth may have already occurred.
- This suggests that abnormal brain development might begin much earlier, potentially before observable behavioral symptoms manifest.
Purpose of the Study:
- To investigate if pathological brain overgrowth precedes the initial clinical signs of autism spectrum disorder (ASD).
- To examine the relationship between the rate of head growth in the first year of life and neuroanatomical and clinical outcomes in early childhood.
Main Methods:
- Retrospective analysis of head circumference (HC), body length, and weight in 48 children with ASD (aged 2-5 years) using longitudinal and cross-sectional normative data.
- Measurements were taken at birth, 1-2 months, 3-5 months, and 6-14 months for a longitudinal group (n=15) and at birth and 6-14 months or birth only for others (n=33).
Main Results:
- Infants with ASD had significantly smaller head circumference at birth (z = -0.66) but exhibited accelerated HC growth (1.67 SDs) by 6-14 months, reaching the 84th percentile.
- Accelerated HC growth from birth to 6-14 months correlated with larger cerebral cortex volume and was observed in 59% of infants with autistic disorder, compared to 6% of healthy infants.
- Birth HC was linked to cerebellar gray matter volume, while rapid postnatal HC increase related to greater cerebral cortex volume in early childhood.
Conclusions:
- Autism onset appears linked to two distinct phases of abnormal brain growth: reduced head size at birth followed by rapid overgrowth between 1-2 and 6-14 months.
- An abnormally accelerated rate of head growth during infancy may serve as a critical early warning sign for the risk of developing autism spectrum disorder.
Context:
Autism most commonly appears by 2 to 3 years of life, at which time the brain is already abnormally large. This raises the possibility that brain overgrowth begins much earlier, perhaps before the first clinically noticeable behavioral symptoms.
Objectives:
To determine whether pathological brain overgrowth precedes the first clinical signs of autism spectrum disorder (ASD) and whether the rate of overgrowth during the first year is related to neuroanatomical and clinical outcome in early childhood.
Design, Setting, And Participants:
Head circumference (HC), body length, and body weight measurements during the first year were obtained from the medical records of 48 children with ASD aged 2 to 5 years who had participated in magnetic resonance imaging studies. Of these children, 15 (longitudinal group) had measurements at 4 periods during infancy: birth, 1 to 2 months, 3 to 5 months, and 6 to 14 months; and 33 (partial HC data group) had measurements at birth and 6 to 14 months (n = 7), and at birth only (n = 28).
Main Outcome Measures:
Age-related changes in infants with ASD who had multiple-age measurements, and the relationship of these changes to brain anatomy and clinical and diagnostic outcome at 2 to 5 years were evaluated by using 2 nationally recognized normative databases: cross-sectional normative data from a national survey and longitudinal data of individual growth.
Results:
Compared with normative data of healthy infants, birth HC in infants with ASD was significantly smaller (z = -0.66, P<.001); after birth, HC increased 1.67 SDs and mean HC was at the 84th percentile by 6 to 14 months. Birth HC was related to cerebellar gray matter volume at 2 to 5 years, although the excessive increase in HC between birth and 6 to 14 months was related to greater cerebral cortex volume at 2 to 5 years. Within the ASD group, every child with autistic disorder had a greater increase in HC between birth and 6 to 14 months (mean [SD], 2.19 [0.98]) than infants with pervasive developmental disorder-not otherwise specified (0.58 [0.35]). Only 6% of the individual healthy infants in the longitudinal data showed accelerated HC growth trajectories (>2.0 SDs) from birth to 6 to 14 months; 59% of infants with autistic disorder showed these accelerated growth trajectories.
Conclusions:
The clinical onset of autism appears to be preceded by 2 phases of brain growth abnormality: a reduced head size at birth and a sudden and excessive increase in head size between 1 to 2 months and 6 to 14 months. Abnormally accelerated rate of growth may serve as an early warning signal of risk for autism.
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