Is there some physiological basis for dyslexic reading behaviour or is it a learning process dysfunction?

Recent brain scans of the thalamus, the part of the brain that serves as its connector, show that the brains of children with dyslexia may be structured differently.

The symptoms of dyslexia are well known and studied. They include struggling to recognize and interpret words while reading as well as trouble with understanding and reading aloud.

However, a majority of dyslexia studies focus on the cerebral cortex. This new research from Vanderbilt University targeted the sub-cortical thalamus area.

The thalamus functions as the brain’s connector. It sends sensory and motor information back to the cerebral cortex through nerve fibers that are part of the brain’s white matter. The thalamus also regulates alertness, consciousness, and sleep.

Diffusion Tensor Imaging the Brain

The researchers assessed 40 children ages 8 to 17 years. The children were divided evenly between normally developing readers and those with developmental dyslexia.

Diffusion tensor imaging was used to visually map the structure of the brain to better comprehend the thalamus’ role in reading behavior.

“A different pattern of thalamic connectivity was found in the dyslexic group in the sensorimotor and lateral prefrontal cortices,” said Laurie Cutting, Vanderbilt University professor.

“These results suggest that the thalamus may play a key role in reading behavior by mediating the functions of task-specific cortical regions. Such findings lay the foundation for future studies to investigate further neurobiological anomalies in the development of thalamo-cortical connectivity in individuals with dyslexia.”

Finding Visual Word Connectivity Patterns

In another study, the same researchers looked at connectivity patterns in a cortical area known to be especially important for reading. That area is the left occipito-temporal region, sometimes known as the visual word form area.

Many previous functional MRI studies have investigated this region, but there is no consensus on the region’s functions. Studies of the visual word form area’s structural connectivity are relatively new.

The team used diffusion MRI to look at the structural connectivity patterns in the left occipito-temporal region and surrounding areas of the brain in 55 children.

“Findings suggest that the architecture of the left occipito-temporal region connectivity is fundamentally different between children who are typically developing readers and those with dyslexia,” Cutting says.

The normal readers showed higher connectivity to linguistic regions than the dyslexic group. Those with dyslexia showed greater connectivity to visual, memory encoding and retrieval regions.

Brain Connect. 2014 Aug;4(6):428-39. doi: 10.1089/brain.2013.0203. Thalamo-cortical connectivity: what can diffusion tractography tell us about reading difficulties in children? Fan Q, Davis N, Anderson AW, Cutting LE

Brain Research Volume 1586, 24 October 2014, Pages 118–129 Structural connectivity patterns associated with the putative visual word form area and children׳s reading ability Fan Q, Davis N, Anderson AW, Cutting LE

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