Fluctuating asymmetry in brain structure and general intelligence in 73-year-olds

Area of Science:

• Neuroscience
• Cognitive Psychology
• Human Development

Background:

• Fluctuating body asymmetry is linked to developmental instability and socioeconomic status (SES).
• Previous research suggests a negative association between fluctuating body asymmetry and cognitive function.
• The relationship between fluctuating brain asymmetry and cognitive abilities remains largely unexplored.

Purpose of the Study:

• To investigate the association between general intelligence and fluctuating asymmetry in four brain structural measures.
• To examine if asymmetry in specific brain regions (Parieto-Frontal Integration Theory - P-FIT) is more related to intelligence.

Main Methods:

• Utilized data from the Lothian Birth Cohort 1936 (N=636, mean age 72.9 years).
• Calculated brain hemispheric asymmetry for cortical surface area, volume, thickness, and white matter fractional anisotropy.
• Employed two methods for asymmetry calculation: equal regional contribution and proportional regional contribution.

Main Results:

• When regions contributed equally, cortical thickness asymmetry was negatively associated with general intelligence (β = -0.18, p < .001).
• Cortical thickness asymmetry showed no association with childhood SES, indicating non-SES related mechanisms.
• No stronger association was found between P-FIT region asymmetry and intelligence compared to non-P-FIT regions.
• When regions contributed proportionally, no significant associations were observed between general intelligence and any asymmetry measure.

Conclusions:

• Cortical thickness asymmetry may be a marker of reduced general intelligence in older adults.
• The method of calculating asymmetry significantly impacts findings, highlighting the need for standardized approaches.
• Developmental factors, rather than socioeconomic status, may underlie the observed asymmetry-intelligence relationship.