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Why is the incidence of learning difficulties higher in boys?

December 20, 2011

When we asked neuroscientist and Speech Pathologist Dr Martha Burns this question, she told us all about the Geschwind-Galaburda hypothesis, which states that differences in maturation rates between the left and right hemispheres of the brain are mediated by circulating testosterone levels, and that sexual maturation acts to fix the hemispheres at stages of development after puberty.

Albert Galaburda (Harvard University) has been studying learning disabilities among males for about thirty years. He originally studied with a man named Norman Geschwind and they began looking at this because stuttering is more common among men (did you see “The King’s Speech”?)

The role of the  left hemisphere

Almost all learning disabilities that involve left hemisphere skills, like reading, language and maths, are more prevalent among boys than girls. Galaburda started speculating very early (his first paper was published in the 80’s), that the left hemisphere, which handles symbols and language, matures at a different stage than the right hemisphere.

In the womb

In the first trimester of pregnancy, neurons are being born, and in the second trimester they are migrating out from the neural tube – first to form the right hemisphere, then the left hemisphere. All of this exactly timed – a foetus by default is a girl, unless testosterone is released in the male foetus and the mother when the neurons are migrating to the left hemisphere.  This burst of testosterone which creates the male genitalia is occurring at exactly the same time as the left hemisphere cells are migrating.

Neuron migration interrupted

Galaburda believed (and now has tremendous research to support this), that testosterone can interrupt the migration in a very subtle way but just enough that you get little cells that migrate to the wrong spot in the left hemisphere (ectopias). You get these little embryonic clusters of neurons that never become neurons because they migrate to the wrong place – and that is what he believes contributes to most of the severe learning disabilities like dyslexia and other learning disabilities that involve migration.

So, it looks like the male brain is more vulnerable to these very specific left hemisphere migratory errors that are associated with learning disabilities that are left hemisphere skills.

Lifelong problems?

Neuroscientists have developed programs to improve left hemisphere skills. With specific training to the affected areas of the brain, age appropriate auditory processing, reading and other left hemisphere skills can be developed.

Interested in learning more about the Fast ForWord program? Have a question about learning, neuroscience and/or education? Contact the team of health and education professionals at Sonic Learning.

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