Numerical and Spatial Networks Underlying the Mental Number Line Edward M. Hubbard1, Philippe Pinel1, Manuela Piazza1 and Stanislas Dehaene1,2 1. INSERM Unit 562, Gif-Sur-Yvette, France 2. College de France
Introduction
Geometrical Relations Between Tasks
Saccadic Eye Movements
• A large body of evidence suggests fundamental connections between number and space in the intraparietal sulcus (for recent reviews see refs. 1,2). • However, these interactions are difficult to explore, as the critical regions lie adjacent to each other. Previous studies have examined the organization of spatial and numerical tasks in the parietal lobe3, but not based on physiological properties. • To better explore the anatomical organization of spatial and numerical tasks, we developed a series of “localizer” tasks, derived from proposed human homologues of monkey regions (see 1 for a review) to identify functional regions of interest (ROIs) based on responsivity to calculation4,5, saccades (LIP)6,7 and multisensory stimulation (VIP)8,9. • We then explored the anatomical and functional overlap between these regions using whole brain SPM, voxel-by-voxel correlation and MDS.
Methods: Tasks and Imaging Parameters • We tested 16 normal adult subjects scanned with a Brucker 3T scanner. • Because IPS activations have been linked to manual response planning, subjects were asked to mentally name result. • Addition and subtraction matched on final result, as illustrated here:
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5
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8
9
Subtraction and Spatial Processes Add Sub Let Sac Tact Flow
Add Sub Let Sac Tact Flow
10 11 12 13 14 15 16 17 18
- Range: subtraction 4-16, addition 4-16 - Average: subtraction 10, addition 10 • Multisensory (VIP) and saccade (LIP) localizers (see methods below).
Functional Correlations Between Eye Movements and Calculation
Add Sub Let Sac Tact Flow
Calculation > Letter Naming
Left Hemisphere
Add Sub Let Sac Tact Flow
Add Sub Let Sac Tact Flow
Add Sub Let Sac Tact Flow
Right Hemisphere
FEF Calculation
Addition 0.3106 0.0929
Subtraction 0.3494 0.0904
Addition 0.5061 0.1745
Subtraction 0.5152 0.1628
VIP
0.2719
0.2967
0.1641
0.0434
LIP
0.0424
0.2278
0.2615
0.2378
Conclusions Localizing Area VIP
Common Networks for Addition and Subtraction
Correlation Between Addition and Subtraction Addition > Subtraction (t > 2.72)
Addition (t > 4.02)
Left Right Hemisphere Hemisphere
Subtraction (t > 4.02)
FEF
0.7889
0.8599
Calculation
0.9104
0.8314
VIP
0.7489
0.6851
LIP
0.8443
0.8809
Conjunction
• Using fMRI we identified parietal and frontal regions involved in mental calculation (addition and subtraction), human homologues of macaque areas LIP and VIP. • These regions partially overlapped and were partially dissociable. • Increased overlap between numerical and spatial processes when –Performing on-line computation (subtraction) –Compared to memory retrieval (addition). • Functional correlations showed significant shared neural mechanisms between calculation and spatial processes, especially in frontal regions. • We find evidence of a partial overlap between multisensory regions (VIP) and calculation. • Whether this difference is due to phylogenetic or ontogenetic factors is an open question for further exploration.
References 1. Hubbard, E.M., Piazza, M. Pinel, P. and Dehaene, S. (2005). Interactions between numbers and space in parietal cortex. Nat. Rev. Neurosci., 6(6): 435448. 2. Fias, W. & Fischer, M. H. (2005) in Handbook of Mathematical Cognition (ed Campbell, J. I. D.) 43-54 (Psychology Press, New York). 3. Simon, O., Mangin, J. F., Cohen, L., Le Bihan, D., and Dehaene, S. (2002). Topographical layout of hand, eye, calculation, and language-related areas in the human parietal lobe. Neuron 33: 475-487. 4. Chochon, F., Cohen, L., Van De Moortele, P. F. & Dehaene, S. (1999). Differential contributions of the left and right inferior parietal lobules to number processing. J. Cognit. Neurosci. 11, 617–630. 5. Dehaene, S., Piazza, M., Pinel, P. & Cohen, L. (2003). Three parietal circuits for number processing. Cognit. Neuropsychol. 20, 487–506. 6. Medendorp, W. P., Goltz, H. C., Villis, T. & Crawford, J. D. (2003). Gaze-centered updating of visual space in human parietal cortex. J. Neurosci. 23, 6209-6214. 7. Medendorp, W. P., Goltz, H. C., Crawford, J. D. & Villis, T. (2005). Integration of target and effector information in human posterior parietal cortex for the planning of action. J. Neurophys. 93, 954-962. 8. Bremmer, F. et al. (2001). Polymodal motion processing in posterior parietal and premotor cortex: a human fMRI study strongly implies equivalencies between humans and monkeys. Neuron 29, 287–296. 9. Sereno, M.I. & Huang, R.S. (2006). A human parietal face area contains aligned head-centered visual and tactile maps. Nat. Neuro. 9(10), 1337-1343.
