Unlike natural numbers, negative numbers do not have natural physical referents. How does the brain represent such abstract mathematical concepts? Two competing hypotheses regarding representational systems for negative numbers are a rule-based model, in which symbolic rules are applied to negative numbers to translate them into positive numbers when assessing magnitudes, and an expanded magnitude model, in which negative numbers have a distinct magnitude representation. Using an event-related functional magnetic resonance imaging design, we examined brain responses in 22 adults while they performed magnitude comparisons of negative and positive numbers that were quantitatively near (difference <4) or far apart (difference >6). Reaction times (RTs) for negative numbers were slower than positive numbers, and both showed a distance effect whereby near pairs took longer to compare. A network of parietal, frontal, and occipital regions were differentially engaged by negative numbers. Specifically, compared to positive numbers, negative number processing resulted in greater activation bilaterally in intraparietal sulcus (IPS), middle frontal gyrus, and inferior lateral occipital cortex. Representational similarity analysis revealed that neural responses in the IPS were more differentiated among positive numbers than among negative numbers, and greater differentiation among negative numbers was associated with faster RTs. Our findings indicate that despite negative numbers engaging the IPS more strongly, the underlying neural representation are less distinct than that of positive numbers. We discuss our findings in the context of the two theoretical models of negative number processing and demonstrate how multivariate approaches can provide novel insights into abstract number representation.
Keywords: number cognition, symbolic number comparisons, distance effect, integers, negative numbers, intraparietal sulcus, prefrontal cortex, representational similarity
Citation: Blair KP, Rosenberg-Lee M, Tsang JM, Schwartz DL and Menon V (2012) Beyond natural numbers: negative number representation in parietal cortex. Front. Hum. Neurosci. 6:7. doi: 10.3389/fnhum.2012.00007
Received: 01 October 2011; Accepted: 18 January 2012;
Published online: 10 February 2012.
Edited by:Seppe Santens, Ghent University, Belgium
Reviewed by:Lars Nyberg, Umeå University, Sweden
Copyright: © 2012 Blair, Rosenberg-Lee, Tsang, Schwartz and Menon. This is an open-access article distributed under the terms of the Creative Commons Attribution Non Commercial License, which permits non-commercial use, distribution, and reproduction in other forums, provided the original authors and source are credited.
*Correspondence: Kristen P. Blair, Stanford University School of Education, Wallenberg Hall, Building 160, 450 Serra Mall, Stanford, CA 94305, USA. e-mail: firstname.lastname@example.org; Miriam Rosenberg-Lee and Vinod Menon, Department of Psychiatry and Behavioral Sciences, 401 Quarry Rd., Stanford University School of Medicine, Stanford, CA 94305-5179, USA. e-mail: email@example.com; firstname.lastname@example.org
† Kristen P. Blair and Miriam Rosenberg-Lee have contributed equally to this work.