Neural correlates of counting large numerosity

The mastery of counting numerosities larger than those correctly estimated by infants or non-human species is an important foundation for the development of higher level calculation skills. The cognitive processes involved in counting are related to spatial attention, language, and number processing. However, the respective involvement of language- and/or visuo-spatial-based brain systems during counting is still under debate. In the present functional magnetic resonance imaging study, we asked 27 right-handed participants to perform an enumeration task on visual arrays of bars that varied in numerosity. Each enumeration condition was contrasted to a color-detection condition that was numerically and spatially matched to the counting condition. The results showed a behavioral discontinuity in response time slopes between large (6–10) and small (1–5) numerosities during enumeration, suggesting that during large enumeration, participants engaged counting processes. Comparing brain regional activity during the enumeration of large numerosity to the enumeration of smaller numerosity, we found increased activation in the bilateral fronto-parietal attentional network, the inferior parietal gyri/intraparietal sulci, and the left ventral premotor and left inferior temporal areas. These results indicated that in adults who master enumeration, counting more than five items requires the strong involvement of spatial attention and eye movements, as well as numerical magnitude processes. Counting large numerosity also recruited verbal working memory areas, subtending a subvocal articulatory code and a visual representation of numbers.