Brain Map Shows Fractions and Integers Share a Single Number Line

Using ultra-high-field 7T fMRI, researchers recorded brain activity while educated adults compared the magnitudes of integer and fraction symbols during an active magnitude comparison task. The study, published in PLOS Biology by Daniela Valério, Samuel Debray, Stanislas Dehaene and colleagues, set out to test whether the mental number line, traditionally described for integers, also absorbs more advanced mathematical concepts such as fractions.

Participants showed both behavioral and neural distance effects: responses depended on the numerical distance between the symbols being compared, a signature of magnitude processing. Activation patterns spanning intraparietal, inferior temporal, prefrontal, hippocampal and parahippocampal cortices could be arranged in a two-dimensional semantic space, with one axis reflecting numerical magnitude and the other separating fractions from integers.

Gaussian fits to the activity data revealed a topographic map of numerical preferences in the anterior inferior parietal cortex, including the anterior intraparietal sulcus and inferior parietal lobule. Crucially, this map was common to both domains, meaning fractions and integers appeared to occupy positions within the same organized cortical representation rather than drawing on separate systems.

The authors caution that the finding applies to educated adults engaged in an explicit magnitude comparison task, so it does not establish how such representations arise through development or how they behave in other contexts. Even so, the results suggest that, in this setting, the brain can construct an ordered, integrated representation of rational and whole numbers, supporting theories that semantic concepts occupy positions in cortical spaces shaped by education.

Subject of Research: Cortical representation of integer and fraction magnitudes in the human brain

Article Title: A cortical semantic map integrates fractions and integers in the human brain

Article References: Valério, D., Debray, S., Karami, A., Cauté, M., Gravel, N., & Dehaene, S. (2026). A cortical semantic map integrates fractions and integers in the human brain. PLOS Biology, 24(10), e3003820. https://doi.org/10.1371/journal.pbio.3003820

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3003820

Keywords: 7T fMRI, numerical cognition, fractions, integers, mental number line, intraparietal cortex, semantic map, magnitude comparison, topographic organization, PLOS Biology, cortical, semantic