Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

Area of Science:

• Neuroscience
• Cognitive Science
• Psycholinguistics

Background:

• Language functions are typically lateralized to the left hemisphere in most right-handed (dextral) individuals.
• The degree of language lateralization in non-right-handed (adextral) individuals remains debated, with conflicting opinions in the scientific community.

Purpose of the Study:

• To investigate and compare the degree of left hemisphere dominance for speech and language functions between dextral and adextral individuals.
• To evaluate the tendency for increased left hemisphere dominance in dextrals compared to adextrals using meta-analytic techniques.

Main Methods:

• A random effects meta-analysis was employed to synthesize findings across various neuroscientific studies.
• Methodological differences in participant recruitment and definition of handedness were largely disregarded to focus on lateralization patterns.

Main Results:

• Despite limitations such as sample size for adextrals and missing data, meta-analyses consistently indicated proportionally greater left hemisphere dominance in dextral participants.
• The findings suggest a subtle but consistent difference in language lateralization between right-handed and non-right-handed individuals.

Conclusions:

• Right-handed individuals exhibit a more pronounced left hemisphere dominance for language functions than non-right-handed individuals.
• These subtle differences hold theoretical importance for understanding the cognitive neuroscience of language and hemispheric asymmetries.