Electrophysiological Evidence for Multiple Representations of Number in the Human Brain

In adult human brains, the horizontal segment of the intraparietal sulcus plays a large role in representing numeric magnitude. In children and non-human primates, however, frontal cortex may play a larger role. We hypothesized that there is a link between observed developmental changes in locus of representation (frontal to parietal) and type of representation used (logarithmic to linear). Participants were presented with number lines and asked to judge accuracy of linear, logarithmic, or log-linear placements. Consistent with hypotheses, event-related potentials generally revealed greatest parietal N1 amplitudes for linear placements and greatest frontal P3 amplitude for logarithmic placements. Additionally, effects of linear placements on cortical activity were moderated by numerical magnitude: parietal N1 amplitudes decreased with magnitude, whereas frontal P3 amplitudes increased with magnitude. These results suggest adults possess logarithmic and linear representations of number, and when logarithmic representations were elicited; there was greater involvement of frontal cortex.