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A new study published in The Journal of Neuroscience offers insight into how small grooves in the brain’s surface — known as tertiary sulci — might help explain individual differences in reasoning ability. Researchers from the University of California, Berkeley, found that the depth of these tiny brain folds in children and adolescents was linked to stronger communication between two areas known to support higher-order thinking: the lateral prefrontal cortex and the lateral parietal cortex. The findings suggest that subtle anatomical variations in these brain folds could influence how efficiently different parts of the brain work together during complex thinking.
The brain’s outer layer, called the cerebral cortex, is characterized by a folded structure with ridges (gyri) and grooves (sulci). These folds allow the large surface area of the cortex to fit within the confines of the skull. While most neuroscience research has focused on the major sulci that are present in nearly everyone, the current study focused on smaller and shallower grooves called tertiary sulci. These sulci tend to vary more across individuals and are found in association areas of the brain — regions that have expanded significantly over the course of human evolution and are involved in advanced cognitive processes.
The rationale for the study stemmed from earlier findings showing that certain sulci in the lateral prefrontal cortex were associated with better reasoning skills in children and adolescents. Building on this, the researchers hypothesized that these small grooves might support reasoning by affecting the structure and function of brain networks. More specifically, they proposed that deeper tertiary sulci might bring distant brain regions closer together, enabling more efficient communication — a concept known as network centrality.
“I’m interested in how prefrontal cortex, roughly the front third of the human brain, supports higher-level cognitive functions like reasoning, in coordination with its faithful sidekick parietal cortex and other regions,” said study author Silvia Bunge, a professor of psychology and a member of UC Berkeley’s Helen Wills Neuroscience Institute.
“I’ve previously studied how variation among individuals can be partially explained by differences among them in terms of particular features of brain anatomy and function. Most recently, I’ve collaborated closely on a number of papers with my colleague Kevin Weiner, a neuroanatomist who specializes in sulcal anatomy and function, showing relationships between specific prefrontal sulci and reasoning performance.”
“Here, we wanted to build on those findings by testing whether the relationships we’ve found between sulcal depth and reasoning performance could be due to the fact that sulcal depth is consequential for brain network activity.”
To examine this, the researchers recruited 43 neurotypical children and adolescents between the ages of 7 and 18 from a larger developmental study of reasoning ability. All participants were right-handed native English speakers and underwent detailed brain imaging while performing a task designed to measure abstract reasoning. The task required them to examine patterns among simple shapes and determine relationships, both at a basic level (e.g., comparing shapes) and at a more complex level (e.g., identifying consistent rules across pairs of shapes). The researchers also collected structural MRI scans to precisely map the sulci in each participant’s brain.
A total of 42 sulci were manually identified in each hemisphere of the brain, focusing on the lateral prefrontal and parietal cortices. The researchers then used functional MRI data collected during the reasoning task to assess how strongly each sulcus was connected to others, essentially building a map of functional connectivity across these grooves. Advanced data analysis techniques were employed to measure three aspects of each sulcus’s role within the brain network: how many other sulci it was connected to (degree), how often it served as a bridge between other connections (betweenness), and how broadly its connections spanned across different functional clusters (participation coefficient).
One key question was whether the sulci had unique patterns of connectivity that distinguished them from one another. The answer was yes. Using machine learning techniques, the team showed that each sulcus had a highly distinctive “connectivity fingerprint,” allowing for 96% accuracy in distinguishing one sulcus from another based on its pattern of functional connections. This high discriminability supported the idea that sulci are not just random anatomical wrinkles but may correspond to functionally meaningful brain units.
Next, the researchers grouped sulci based on the similarity of their connectivity patterns. They found five major clusters, with some groups containing both prefrontal and parietal sulci and others consisting solely of prefrontal sulci previously linked to reasoning.
Interestingly, some of these clusters were distinct from the large-scale brain networks typically identified in studies of resting-state brain activity. This suggests that using sulci as the basic unit of analysis could offer a more personalized and anatomically grounded approach to studying brain function.
A key finding was that in several specific tertiary sulci — including the right pmfs-a, left pmfs-i, and left pimfs — greater depth was linked to higher network centrality. In other words, these deeper sulci tended to have stronger and more distributed connections across the brain network, particularly with other important sulci involved in vision and attention.
These relationships held even after accounting for age and head motion, and were not driven solely by proximity to other sulci. The findings support the idea that deeper tertiary sulci may promote greater neural efficiency by facilitating shorter and more direct communication between key brain areas.
“For some specific sulci, the deeper the sulcus the better integrated it was within the network of prefrontal and parietal sulci we examined — i.e., the more tightly coupled its activation was with a number of other sulci.”
These associations were not uniform across all sulci. Some sulci with large surface areas, such as those in the intraparietal sulcus, had higher centrality measures overall, but did not show the same depth-dependent variation as the tertiary sulci. The researchers also found that the link between sulcal depth and network connectivity was not confined to sulci previously linked to reasoning ability. For instance, similar relationships were observed in a sulcus called aipsJ, which is sometimes used as a neurosurgical corridor, and a newly identified sulcus in the parietal lobe known as slocs-v.
These results lend support to a long-standing hypothesis that individual variability in sulcal anatomy could play a functional role in cognition. The idea dates back to the 1960s, when neuroanatomist Sanides proposed that subtle differences in sulcal structure might reflect and even shape cognitive abilities. The current findings suggest that sulcal depth, especially in regions that develop late in gestation and continue to change during childhood, could serve as a biomarker for individual differences in reasoning and possibly other mental functions.
“Sulcal patterns are not random, and are linked with cognition and functional organization. Fine-grained individual anatomy may help in developing tools and grounded hypotheses to better account the high individual variability between people,” said co-author Suvi Häkkinen, an assistant project scientist.
“We went into the study with the hypothesis that functional connectivity (that is, patterns of coordinated brain activation across a set of regions) could be the missing link explaining relationships between sulcal depth and cognition that we had previously found,” Bunge added, “but it was a wide open question as to whether we’d find any relation between depth and functional connectivity. It was a nice surprise that it turned out as it did!”
“I was surprised to learn from Suvi’s analyses just how well a pattern classifier could distinguish sulci — even small, neighboring sulci — from one another based on their connectivity fingerprints (i.e., their patterns of coupling to other regions). I was also surprised that some of the prefrontal sulci had more similar functional fingerprints to certain parietal sulci than to other prefrontal sulci.”
Despite its strengths, the study has several limitations. The amount of functional MRI data collected per participant was relatively modest, which may limit the precision of individual-level network measures. The sample was also restricted to children and adolescents, leaving open the question of whether similar patterns exist in adults or in individuals with neurodevelopmental disorders. In addition, while the study used rigorous control analyses to address confounds like head motion and spatial proximity, some residual effects cannot be ruled out.
Future research could expand this approach to different brain regions, age groups, and cognitive domains. The method of defining brain networks based on sulcal anatomy — rather than predefined regions or general brain atlases — may offer a more individualized way to study brain function. It could also help identify early anatomical markers for cognitive strengths and vulnerabilities, potentially informing education, clinical interventions, and neuroscience-based diagnostics.
The study, “Anchoring functional connectivity to individual sulcal morphology yields insights in a pediatric study of reasoning,” was authored by Suvi Häkkinen, Willa I. Voorhies, Ethan H. Willbrand, Yi-Heng Tsai, Thomas Gagnant, Jewelia K. Yao, Kevin S. Weiner, and Silvia A. Bunge.
