The evolutionary mystery of how the brain learns to read
New research sheds light on the brain's origins of reading ability.
1An evolutionary puzzle
Reading is a very recent skill in human evolution, so the brain doesn't have a dedicated area for it. Instead, our brain repurposes systems that evolved for other functions. The new research investigates which systems are involved in this process and how they adapt. These findings could explain why some people learn to read more easily than others.
2Twin comparison study
The study compared brain structures and reading skills of twins with varying degrees of genetic similarity. High-resolution brain scans from the Human Connectome Project were used. Participants didn't read during scanning but completed various language tests. Among these, the ability to read written words aloud was measured as a key indicator of reading skill.
3Heritable connections
The researcher examined the relationship between reading skills and fine brain structure. Several brain areas contributing to reading-related skills were identified, some showing heritable links. However, heritability doesn't mean an unchangeable fate. The brain has a constantly changing structure, and these initial conditions are shaped throughout life.
4Role of auditory skills
When learning to read, we first learn to identify and combine sounds in our minds. In developmental dyslexia, difficulties in perceiving the sound structure of language are commonly cited. Children create words by mapping letters to sounds. This process requires the ability to distinguish speech sounds at the syllable level.
5Importance of temporal lobe
The medial belt area in the left temporal lobe is sensitive to slow, coarse sound changes. This area's well-organized neural structure was found linked to reading ability. The relationship has a genetic component, suggesting perceptual system organization may influence reading ease. These differences contribute to literacy variation across the entire population.
6Visual recognition and face perception
A skilled reader can instantly connect words to their meanings. Visual word recognition works similarly to our face discrimination capacity. The size of the dorsal temporal pole in the right anterior temporal lobe was found connected to reading ability, with this combination being heritable. This region may help recognize words similarly to how we recognize faces.
7Access to word meaning
The anterior middle temporal gyrus in the left temporal lobe is thought to connect word form and meaning. Larger size of this area improves our ability to decipher meanings. Easier access to word meanings may facilitate reading acquisition. Indeed, this region's size was also genetically related to reading ability.
8Experience shapes the skill
After understanding the brain's initial conditions for reading ability, we can examine how this skill develops. After detecting syllables, speech sound distinctions need refinement. This requires primary auditory cortex to perform fine-grained sound analysis. Here, a thicker cortex is associated with better reading skills.
9Impact of neuroplasticity
The study found that the combination of reading skill and thick cortex wasn't genetically driven. Instead, experiences—like exposure to speech sounds and other auditory analyses—likely shape this connection. These findings highlight the importance of neuroplasticity in how the brain learns reading skills.
10Society-wide implications
This research shows reading skill differences exist not just between dyslexic and non-dyslexic individuals, but across the entire population spectrum. Findings suggest educational approaches should adapt to individual differences. Understanding the brain's reading mechanisms could help develop new interventions for learning difficulties.