Human intraparietal sulcal morphology relates to individual differences in language and memory performance

The sulco-gyral pattern, a qualitative feature of cortical anatomy established in utero and stable throughout life, is linked to brain function. While the intraparietal sulcus (IPS) is a key associative brain area, its morphological relationship with cognition remains largely unexplored. This study aims to bridge this gap by investigating whether variations in IPS morphology, specifically the presence or absence of an interruption in the horizontal branch (hIPS), are associated with differences in cognitive abilities. Previous research has shown links between sulcal patterns and specific cognitive domains, such as the anterior cingulate cortex (ACC) and cognitive control, and the occipito-temporal sulcus (OTS) and reading. However, a comprehensive analysis of IPS morphology and its broader cognitive correlates is lacking. The IPS's role as a nodal associative area, connecting sensorimotor, visual, and higher-order cognitive regions, makes it a prime candidate for studying the link between morphology and multiple cognitive functions. The study utilizes data from the Human Connectome Project (HCP), a valuable resource offering a large dataset of behavioral and neuroimaging measures, ensuring robust statistical power. By focusing on a defined age range (26-30 years old) the researchers minimize potential age-related confounds, improving the precision of their findings. This study is crucial as it seeks to move beyond the limitations of previous studies, which focused on a priori selected cortical areas and a single cognitive domain. By employing a data-driven approach using principal component analysis (PCA), they aim to uncover relationships between hIPS morphology and a broad range of cognitive abilities. The expected outcome is to identify whether an interruption in the hIPS confers a cognitive advantage beyond previously established numerical abilities.

Several studies have explored the link between sulcal patterns and cognition. Research on the ACC has demonstrated associations between its morphological variations (single or double parallel patterns) and cognitive control. Similarly, studies on the OTS have revealed a positive correlation between an interrupted pattern and reading performance. Furthermore, a sectioned hIPS has been linked to better math fluency. These studies suggested that interrupted sulcal patterns might relate to enhanced underlying white matter organization, potentially due to increased fiber number, diameter, or myelination. However, most previous research focused on specific areas and cognitive domains, based on a "one-to-one mapping" hypothesis. The current study differs by considering the IPS, a multimodal associative area involved in various cognitive processes, including visuospatial attention, motor intention, calculation, memory, and language. The researchers aim to expand upon previous work by exploring the broader cognitive implications of IPS morphology variation in a large sample, moving beyond the focus on single cognitive domains and specific brain regions.

This study utilized data from the Human Connectome Project (HCP) 1200 Subjects Release (S1200), selecting 390 participants aged 26–30 years. Exclusion criteria included quality control issues, neurological diseases, and psychiatric or medical disorders. The sample comprised 173 males (44%). The researchers manually labeled the horizontal branch of the intraparietal sulcus (hIPS) on inflated and pial cortical surfaces, classifying it as either "interrupted" or "continuous." Two experts independently labeled the hIPS, with a third expert resolving disagreements (inter-rater reliability of 87–88%). A binomial test compared the frequency of interrupted and continuous patterns. Logistic regression assessed the effects of sex and hemisphere on hIPS interruption. A χ² analysis compared hIPS pattern distribution across the current study and three previous studies. Eighteen behavioral measures from twelve cognitive tasks across eight domains were collected. Principal Component Analysis (PCA) reduced the dimensionality of the behavioral data, identifying five principal components representing common cognitive variance: Memory and Language, Executive Functions, Impulsivity, Attention, and Intelligence and Spatial Orientation. A Generalized Linear Model (GLM) examined the relationship between hIPS morphology (left and right), sex, and the five PCA factors. A control analysis included cortical thickness of the superior and inferior parietal lobules as covariates in the GLM. All statistical analyses were conducted using IBM SPSS Statistics 25.

The study found a prevalence of the interrupted hIPS pattern in the right hemisphere (69.23%), significantly different from the left hemisphere (47.44%). Logistic regression indicated that sex and hemisphere significantly influenced hIPS interruption; males showed a higher prevalence of interrupted hIPS than females. Comparison with previous studies revealed significant differences in left hIPS pattern distribution but not in the right hIPS. PCA identified five cognitive factors. GLM analysis revealed a significant main effect of right hIPS pattern on the "Memory and Language" factor (F=13.176; df=1; p=0.0003), with interrupted hIPS associated with better performance. Sex also showed a significant main effect on this factor, with females performing better. Significant sex effects were also observed for "Executive Functions" and "Intelligence and Spatial Orientation." Control analyses showed no significant effect of cortical thickness on the relationship between right hIPS pattern and Memory and Language performance.

This study demonstrates a robust association between right hIPS morphology and performance in memory and language tasks, even controlling for cortical thickness. The finding of a right-hemisphere effect is noteworthy, considering the typical left-hemisphere lateralization of these functions. This suggests a potential role for the right hIPS in early cognitive development and plasticity before full lateralization. The interrupted hIPS pattern may reflect an increased amount of cortical tissue and connections, supporting neuroplasticity and cognitive function acquisition. The inconsistencies in left hIPS pattern distributions across studies highlight the need for larger, standardized samples. Future research should investigate the role of hIPS morphology in sensorimotor and visuospatial abilities and its relationship to underlying white matter pathways, particularly the Parietal Angular-to-Supramarginal tract (PAS) and the Parietal Inferior to Post-central tract (PIP). Further investigation into the role of hIPS morphology in language and memory development in children is warranted.

This study is the first to comprehensively investigate the relationship between hIPS sulcal pattern and various cognitive domains in a large sample of healthy adults. The findings reveal a robust association between right hIPS interruption and improved performance in memory and language tasks. These results underscore the importance of considering the non-dominant hemisphere's role in cognitive development, even for typically lateralized functions. Future research should focus on clarifying the underlying white matter connections and investigating this relationship in children.

The study's reliance on the HCP dataset limits generalizability, as the sample may not fully represent the broader population. Manual labeling, although with high inter-rater reliability, introduces subjective bias. The lack of certain tasks (sensorimotor/visuospatial) in the HCP dataset prevented a more complete assessment of hIPS morphology's relationship with cognitive abilities.