Among several significant studies involving childhood in 2006, scientists pinpointed specific areas of the brain that contribute to enlarged brain size, which commonly occurs in autism spectrum disorder. Researchers also gained new insights into some of the neuroanatomical and biochemical differences that appear to be responsible for the cognitive difficulties experienced by children with attention-deficit/hyperactivity disorder, and more evidence emerged regarding the role of viral infections in developmental disorders such as cerebral palsy.

Brain Abnormalities in Autism

Autism spectrum disorder (ASD), a grouping that includes autism and disorders similar to it, is a pervasive developmental disorder manifested primarily in greatly diminished social interaction and communication skills. No one knows exactly what causes ASD, but scientists have identified many neurological abnormalities that might contribute to the social and cognitive deficits typically observed in ASD.

Abnormal activity in specific brain regions has been associated with ASD. For example, a part of the brain called the inferior frontal gyrus was markedly less active in children with ASD during the performance of certain tasks related to social interaction, according to a research team led by Marco Iacoboni, a neuroscientist at the University of California, Los Angeles.¹

In a study reported in Nature Neuroscience, Iacoboni’s team used functional magnetic resonance imaging to investigate neural activity of 10 high-functioning children with ASD and 10 normally developing children as the children observed and imitated facial emotional expressions. The degree of reduced activity correlated with the severity of their symptoms.

The inferior frontal gyrus is believed to be part of the so-called mirror neuron system, which plays an important role in the perception and expression of emotions and enables individuals to experience empathy. The findings indicate that a dysfunctional mirror neuron system may underlie the social deficits observed in autism.

Abnormalities in brain size also have been associated with ASD. In a study published in the American Journal of Psychiatry, a group of researchers led by Antonio Hardan, a Stanford University psychiatrist, used magnetic resonance imaging scans to compare the size of the cortex (the outer layer of the brain) between 17 children with autism and 14 children without the disorder.² Cortical thickness is a sensitive index of normal brain development. 

1. Dapretto M, Davies MS, Pfeifer JH, Scott AA, Sigman M, Bookheimer SY, and Iacoboni M. Understanding emotions in others: Mirror neuron dysfunction in children with autism spectrum disorders. Nature Neuroscience 2006 9(1):28–30.

2. Hardan AY, Muddasani S, Vemulapalli M, Keshavan MS, and Minshew NJ. An MRI Study of Increased Cortical Thickness in Autism. American Journal of Psychiatry 2006 163(7):1290–1292.

3. Munson J, Dawson G, Abbott R, Faja S, Webb SJ, Friedman SD, Shaw D, Artru A, and Dager SR. Amygdala volume and behavioral development in autism. Archives of General Psychiatry 2006 63(6):686–693.

4. Petropoulos H, Friedman SD, Shaw DWW, Artru AA, Dawson G, and Dager SR. Gray matter abnormalities in autism spectrum disorder revealed by T2 relaxation. Neurology 2006 67(4):632–636.

5. Gilbert DL, Wang Z, Sallee FR, Ridel KR, Merhar S, Zhang J, Lipps TD, White C, Badreldin N, and Wassermann EM. Dopamine transporter genotype influences the physiological response to medication in ADHD. Brain 2006 129(Pt. 8):2038–2046.

6. Smith AB, Taylor E, Brammer M, Toone B, and Rubia K. Task-specific hypoactivation in prefrontal and temporoparietal brain regions during motor inhibition and task switching in medication-naive children and adolescents with attention deficit hyperactivity disorder. American Journal of Psychiatry 2006 163(6):1044–1051.

7. Shaw P, Lerch J, Greenstein D, Sharp W, Clasen L, Evans A, Giedd J, Castellanos FX, and Rapoport J. Longitudinal mapping of cortical thickness and clinical outcome in children and adolescents with attention-deficit/hyperactivity disorder. Archives of General Psychiatry 2006 63(5):540–549.

8. Gibson CS, MacLennan AH, Goldwater PN, Haan EA, Priest K, and Dekker GA. Neurotropic viruses and cerebral palsy: Population based case-control study. British Medical Journal 2006 332(7533):76–80.