As the child grows into adolescence, the functions of the corresponding areas on the left and right sides of the brain are no longer the same, reflecting the transition to specialized mental labor. A recent study observed that people with superior intelligence scores experience this functional division at an accelerated rate. These findings were published in the journal *Developmental Cognitive Neuroscience*.
The human brain has two different parts. These left and right hemispheres frequently communicate to manage everything from basic sensory input to advanced reasoning. Historically, discussions about brain organization have focused on spatial lateralization. This concept suggests that certain cognitive areas, such as language processing and spatial cognition, are highly dependent on one side of the brain.
In reality, both hemispheres always work together to support cognitive demands. To understand this cooperation, neuroscientists measure functional homotopy. This concept explains the similarities in brain activity between mirroring areas in the left and right hemispheres. High-functioning homotopy means that both sides of the brain perform identical or highly synchronized roles. Low-functioning homotopy indicates that the hemispheres have differentiated duties to operate independently to some degree.
Researchers Li-Zhen Chen and Xi-Nian Zuo started this study to understand how this interhemispheric coordination evolves as children grow older. Chen and Zuo are cognitive neuroscience researchers based at Beijing Normal University. They wanted to track the maturation of brain networks from infancy to adolescence and see how physical brain organization relates to cognitive abilities.
During early childhood, neural networks are typically widely distributed. Young brains maintain high levels of synchronous communication across both hemispheres. Over time, the brain develops greater functional specialization. This developmental change allows the mind to move from generalized networks to specialized configurations that can support advanced reasoning.
To observe these changes, Chen and Zuo analyzed longitudinal data and intelligence test scores. This cohort included 178 participants ranging from 6 years old to nearly 17 years old. The researchers obtained multiple resting-state functional magnetic resonance imaging scans from the participants over several years. This scanning technique allowed researchers to observe spontaneous brain activity while participants rested in the scanner with their eyes open.
Measuring this communication involves assessing changes in blood oxygen in the brain over time. This scanning technology tracks how oxygenated blood moves to active neurons. If the oxygenation patterns match perfectly between mirroring brain regions in the left and right halves, it indicates a high degree of synchronization. A decrease in this measurement indicates that a distinct localized firing pattern is occurring in the corresponding region.
Alongside the brain scans, participants completed a standard cognitive assessment to measure intelligence quotient. The researchers divided the participants by age, grouping them into children under 12 and adolescents over 12. They also divided participants into average, high intelligence, and excellent intelligence groups based on behavioral test results.
To quantify brain changes, the research team used mathematical metrics to assess functional connectivity profiles across the brain. This measurement allowed them to map how both sides of the brain communicate similarly with other parts of the nervous system. By comparing these maps across ages and intelligence levels, we can precisely track rates of hemispheric specialization.
The analysis revealed that activity in the left and right hemispheres declines in tandem with age. Younger children showed greater similarity between brain hemispheres. Older adolescents showed lower overall similarity and a more adult-like pattern of hemispheric independence.
Brain development follows specific physical pathways that map from core sensorimotor areas to advanced cognitive areas as people age. Areas that handle basic sensory information, such as vision and touch, mature early in life. Areas that process abstract ideas and integrate multiple types of sensory information mature much later.
The most pronounced decline in hemispheric harmony occurred within these higher-order association networks. These neural networks manage sophisticated tasks related to memory, attention, and executive control. Primary regions responsible for basic sensory processing showed weak age-related changes across the general sample. As adolescents approach adulthood, their brain systems essentially delegate different parts of complex cognitive tasks to separate hemispheres.
During early childhood, interconnected nervous systems that handle internal thought processes operate similarly on both sides of the brain. When older young people use the same network to recall memories or imagine future events, the left and right sides operate differently. The left side handles the linguistic component of a concept, and the right side manages the social or emotional component.
Comparing neuroimaging data with intelligence scores revealed distinct developmental patterns. In the childhood group, the correlation between brain similarity and intelligence was relatively weak. By adolescence, decreased synchronized brain activity was associated with increased intelligence scores.
Following participants over time revealed different developmental trajectories across intelligence groups. Children in the superior intelligence group had the fastest overall rate of decline in hemispheric similarity. By age 17, this group had the lowest levels of symmetrical brain activity compared to other groups.
The group with greater intelligence also showed neural changes in different physical locations. The average and high intelligence groups only showed significant specialization in advanced association networks, whereas the superior group showed these changes uniformly across the brain. Even their primary sensory and visual networks developed a high degree of hemispheric independence.
Modern theories of neurodevelopment suggest that highly intelligent individuals integrate brain networks more efficiently. The accelerated decline in synchronous activity may reflect an earlier, more advanced state of hemispheric specialization. By efficiently dividing labor between the left and right halves of the brain, a person can use fewer physical resources to complete complex mental operations.
The study design has certain limitations, which the researchers plan to address in future analyses. The direct correlation between calculated intelligence scores and brain symmetry was not statistically significant at all data points, reflecting natural variability in human development. The researchers also focused exclusively on the outer layer of the brain, known as the cerebral cortex.
Some integrated communication hubs reside deeper in the subcortical regions of the brain. Structures like the thalamus relay sensory information and are involved in intellectual processing, but their developmental patterns were not assessed in this study. By investigating these regions, similar mapping techniques could potentially be extended to include the entire central nervous system.
The observed sample size also limited our ability to analyze biological sex differences in brain development. Although the researchers mathematically controlled for a wide range of gender differences, a larger group of participants is needed to map out the specific developmental trajectories of boys and girls. Tracking these differences may ultimately help medical professionals understand atypical patterns of brain development in learning and cognitive disorders.
The study, “Intellectual ability and cortical homotopy development in children and adolescents,” was authored by Li-Zhen Chen and Xi-Nian Zuo.
