A new study published in the journal Nature Communications sheds light on how our preference for using one hand over the other — known as handedness — is reflected in brain functioning, specifically among 9- to 10-year-old children. The study reveals a profound association between handedness and the functional architecture of the brain, without significant differences in the brain’s structure.
Previous research has established that handedness emerges early in life, influenced by a blend of genetic, environmental, and neurodevelopmental factors. However, the exact relationship between handedness and the lateralized (side-specific) organization of the brain, particularly in children, has remained largely uncharted territory.
“My interest on the effect of handedness on brain connectivity patterns in children due to its potential to unravel fundamental aspects of human brain organization and development,” explained study author Dardo Tomasi, a senior staff scientist and MRI physicist at the National Institute of Alcohol Abuse and Alcoholism’s Laboratory of Neuroimaging.
“Handedness has long fascinated researchers for its connection to lateralized brain functions and behaviors. The neural correlates of handedness, particularly in children, offer a unique opportunity to better understand the underlying mechanisms shaping brain connectivity and organization during critical developmental stages.”
The researchers leveraged data from the Adolescent Brain Cognitive Development (ABCD) study, which provided a wealth of information on children aged 9 to 10 years from various demographics across the United States. For the current study, the researchers focused on a sample of 1,800 children from the ABCD dataset, divided evenly into three groups based on their handedness: 600 left-handed, 600 right-handed, and 600 mixed-handed.
The cornerstone of the methodological approach was the use of resting-state functional MRI (fMRI) data to investigate the functional connectivity patterns across the brain. Functional connectivity refers to the temporal correlation between neuronal activation patterns of different brain regions, offering insights into how different parts of the brain communicate during rest. This was complemented by structural MRI scans to assess brain morphometrics (such as cortical thickness, sulcal depth, and cortical myelin content) and diffusion MRI to explore white matter microstructure.
The researchers observed a strong association between handedness and the laterality of functional connectivity patterns in the brain. Specifically, left-handed children demonstrated increased functional connectivity in the left-hand motor area of the brain (located in the right hemisphere) and decreased connectivity in the right-hand motor area (located in the left hemisphere). This pattern was distinct when compared to right-handed and mixed-handed children, suggesting a unique functional neural architecture associated with left-handedness.
Interestingly, the researchers discovered that handedness in children was not only associated with differences in the functional connectivity of the brain’s hand-motor network but also influenced the connectivity patterns across a broader network of brain regions. They also found variations in the laterality of connectivity involving other sensory-motor regions, as well as heteromodal cortical areas (which integrate information from multiple sensory regions) and the cerebellum (which is involved in coordinating motor actions).
Remarkably, these differences in functional connectivity did not coincide with differences in structural connectivity, brain morphometrics, or cortical myelin content. This suggests that the functional asymmetries linked to handedness are not simply a reflection of underlying structural asymmetries in the brain.
“The increased functional connectivity of the hand motor areas among left-handed children compared to right-handed counterparts was our main hypothesis,” Tomasi told PsyPost. “However, the variability in hand-motor connectivity across different brain regions, and the absence of significant structural differences between left, right, and mixed-handed children challenged our previous assumptions about the neural correlates of handedness.”
These findings are significant because they demonstrate that handedness is associated with a broad network of brain connectivity differences, not just in areas directly involved in controlling hand movements. This suggests that the preference for using one hand over the other is a manifestation of a wide-reaching neural basis that influences a variety of brain functions.
“Understanding that handedness is not merely a behavioral trait but is intricately linked to distinct patterns of brain connectivity can foster a deeper appreciation for the complexity of human brain development,” Tomasi explained. “Recognizing that differences in brain connectivity exist between left-handed and right-handed individuals, particularly in motor areas, highlights the diversity and individuality of brain organization.
“Moreover, our study underscores the importance of considering handedness as a factor in understanding cognitive and motor functions, emphasizing the need for personalized approaches in education, rehabilitation, and other domains that rely on fine motor skills and cognitive abilities. Ultimately, this research contributes to a broader understanding of human brain function and underscores the importance of embracing diversity in brain organization among individuals.”
However, this study, like all scientific endeavors, has its limitations. “The study’s reliance on cross-sectional data limits its ability to infer developmental trajectories or changes over time in brain connectivity related to handedness,” Tomasi noted. “Furthermore, the generalizability of the findings may be influenced by factors such as the specific age range of participants, sample demographics, and the methods used to assess handedness and brain connectivity.”
“Given the longitudinal nature of the ABCD study, in the future we aim to investigate how handedness-related brain connectivity patterns evolve across different developmental stages, from childhood to adolescence and adulthood, to gain insights into the dynamic nature of brain organization and plasticity.”
The study, “Associations between handedness and brain functional connectivity patterns in children,” was authored by Dardo Tomasi and Nora D. Volkow.