Planum temporale asymmetry in developmental dyslexia: Revisiting an old question

Hum Brain Mapp. 2014 Dec;35(12):5717-35. doi: 10.1002/hbm.22579. Epub 2014 Jul 10.


Among the various asymmetrical structures of the human brain, the planum temporale, an anatomical region associated with a variety of auditory and language-related processes, has received particular attention. While its surface area has been shown to be greater in the left hemisphere compared to the right in about two-thirds of the general population, altered patterns of asymmetry were revealed by post mortem analyses in individuals with developmental dyslexia. These findings have been inconsistently replicated in magnetic resonance imaging studies of this disorder. In this report, we attempt to resolve past inconsistencies by analyzing the T1-weighted MR images of 81 children (mean age: 11 years, sd: 17 months), including 46 control (25 boys) and 35 dyslexic children (20 boys). We manually outlined Heschl's gyri, the planum temporale and the posterior rami of the Sylvian fissure on participants' brain images, using the same anatomical criteria as in post mortem studies. Results revealed an altered pattern of asymmetry of the planum temporale surface area in dyslexic boys only, with a greater proportion of rightward asymmetrical cases among dyslexic boys compared to control boys. Additionally, analyses of cortical thickness showed no asymmetry differences between groups for any of the regions of interest. Finally, a greater number of Heschl's gyrus full duplications emerged for the right hemisphere of dyslexic boys compared to controls. The present findings confirm and extend early post mortem observations. They also stress the importance of taking gender into account in studies of developmental dyslexia.

Keywords: developmental dyslexia; gender; planum temporale; reading; structural magnetic resonance imaging.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cerebral Cortex / pathology*
  • Child
  • Dyslexia / pathology*
  • Female
  • Functional Laterality
  • Humans
  • Language Tests
  • Magnetic Resonance Imaging
  • Male
  • Neuropsychological Tests
  • Organ Size
  • Sex Characteristics