Middle temporal cortex is involved in processing fractions.

Numerous studies have examined how the brain processes numbers. However, although much attention has been paid to whole numbers, little is known about fractions, despite their pervasive use and the large number of people who have difficulty in learning them. We hypothesized that effective processing of fractions relies on conceptual knowledge. To test this hypothesis, we recorded functional magnetic resonance imaging signals from 68 participants (34 females and 34 males) when they performed a magnitude comparison task (whole number vs. fraction) with different levels of difficulty (short-distance number pairs vs. long-distance number pairs), and examined whether brain regions that handle conceptual knowledge are more involved in processing fractions than in processing whole numbers. Spatial patterns for brain activity related to processing fractions and whole numbers differed greatly in the left middle temporal gyrus (MTG) as well as in the parietal and frontal cortices. Further analysis showed that activation patterns in the left MTG differed between tasks, but activation intensity did not. In contrast, no significantly different activation patterns were found between short-distance and long-distance conditions in the left MTG. Additionally, functional connectivity (FC) from the left MTG to the intraparietal sulcus (IPS) was stronger when processing fractions than when processing whole numbers, regardless of the distance between numbers (short or long). However, similar effect was not detected between short-distance and long-distance conditions. Further, FC strength from the left MTG to the IPS positively correlated with accuracy in comparing fractions. The results suggest that the left MTG plays a critical role in processing fractions.