Laterality and types of dyslexia

Area of Science:

• Neuroscience
• Genetics
• Developmental Psychology

Background:

• Cerebral specialization and handedness involve complex genetic and developmental factors.
• The right shift theory posits a specific human factor enhancing left hemisphere advantage and right-handedness.
• Random lateral asymmetries exist across species, with a human-specific factor influencing handedness.

Purpose of the Study:

• To investigate the genetic basis of handedness and cerebral specialization using the right shift theory.
• To explore the relationship between genetic models of handedness and developmental dyslexia.
• To test the hypothesis that different genotypes are associated with distinct cognitive deficits in reading.

Main Methods:

• Estimation of gene frequency for the right shift (rs) gene based on dysphasia lesion data.
• Modeling handedness distribution in families to infer genetic inheritance patterns.
• Analyzing cognitive profiles and handedness in individuals with developmental dyslexia based on predicted genotypes.

Main Results:

• Genetic modeling suggests a balanced polymorphism with heterozygote advantage for laterality and cognitive abilities.
• The right shift theory applied to dyslexia predicts homozygotes (rs-- and rs++) are at risk for reading difficulties.
• Evidence supports a double dissociation: speech-based processing issues in rs-- and non-speech based issues in rs++, correlating with specific handedness patterns.

Conclusions:

• The right shift theory provides a viable genetic model for handedness and its link to cerebral specialization.
• Genetic factors influencing handedness may play a significant role in the etiology of developmental dyslexia.
• Distinct cognitive deficits associated with specific genotypes offer insights into the neurobiological underpinnings of reading disorders.