Experimental Brain Research

, Volume 236, Issue 4, pp 1129–1138 | Cite as

The neural circuits of number and letter copying: an fNIRS study

  • Christina Artemenko
  • Andra Coldea
  • Mojtaba Soltanlou
  • Thomas Dresler
  • Hans-Christoph Nuerk
  • Ann-Christine Ehlis
Research Article


In our daily lives, we are constantly exposed to numbers and letters. However, it is still under debate how letters and numbers are processed in the brain, while information on this topic would allow for a more comprehensive understanding of, for example, known influences of language on numerical cognition or neural circuits shared by numerical cognition and language processing. Some findings provide evidence for a double dissociation between numbers and letters, with numbers being represented in the right and letters in the left hemisphere, while the opposing view suggests a shared neural network. Since processing may depend on the task, we address the reported inconsistencies in a very basic symbol copying task using functional near-infrared spectroscopy (fNIRS). fNIRS data revealed that both number and letter copying rely on the bilateral middle and left inferior frontal gyri. Only numbers elicited additional activation in the bilateral parietal cortex and in the left superior temporal gyrus. However, no cortical activation difference was observed between copying numbers and letters, and there was Bayesian evidence for common activation in the middle frontal gyri and superior parietal lobules. Therefore, we conclude that basic number and letter processing are based on a largely shared cortical network, at least in a simple task such as copying symbols. This suggests that copying can be used as a control condition for more complex tasks in neuroimaging studies without subtracting stimuli-specific activation.


Number processing Letter processing Copying task fNIRS 



This research was supported by the LEAD Graduate School & Research Network (GSC1028), which is funded within the framework of the Excellence Initiative of the German federal and state governments. This research was further funded by a Grant from the Science Campus Tübingen, project 8.4 to HCN supporting MS. MS was also supported by the DFG Grant (NU 265/3-1) to HCN. ACE was partly supported by the IZKF Tübingen (Junior Research Group, Grant 2115-0-0). We would like to thank Minako Uga and Ippeita Dan for their help in preparing the spatial registration and anatomical labeling of fNIRS channels. We would also like to thank our research assistants for their help in data collection and language proofreading of the manuscript.


  1. Abboud S, Maidenbaum S, Dehaene S, Amedi A (2015) A number-form area in the blind. Nat Commun 6:6026. PubMedPubMedCentralCrossRefGoogle Scholar
  2. Acheson DJ, Hagoort P (2013) Stimulating the brain’s language network: syntactic ambiguity resolution after TMS to the inferior frontal gyrus and middle temporal gyrus. J Cogn Neurosci 25(10):1664–1677. PubMedCrossRefGoogle Scholar
  3. Amalric M, Dehaene S (2016) Origins of the brain networks for advanced mathematics in expert mathematicians. Proc Natl Acad Sci 113(18):4909–4917. PubMedPubMedCentralCrossRefGoogle Scholar
  4. Ansari D (2008) Effects of development and enculturation on number representation in the brain. Nat Rev Neurosci 9(4):278–291. PubMedCrossRefGoogle Scholar
  5. Ansari D (2016) The neural roots of mathematical expertise. Proc Natl Acad Sci 113(18):4887–4889. PubMedPubMedCentralCrossRefGoogle Scholar
  6. Arsalidou M, Taylor MJ (2011) Is 2 + 2 = 4? Meta-analyses of brain areas needed for numbers and calculations. NeuroImage 54(3):2382–2393. PubMedCrossRefGoogle Scholar
  7. Baldo JV, Dronkers NF (2007) Neural correlates of arithmetics and language comprehension: a common substrate? Neuropsychologia 45:229–235. PubMedCrossRefGoogle Scholar
  8. Carreiras M, Quiñones I, Hernández-Cabrera JA, Duñabeitia JA (2015) Orthographic coding: brain activation for letters, symbols, and digits. Cereb Cortex 25(12):4748–4760. PubMedCrossRefGoogle Scholar
  9. Chan AM, Dykstra AR, Jayaram V, Leonard MK, Travis KE, Gygi B, Baker JM, Eskandar E, Hochberg LE, Halgren E, Cash SS (2014) Speech-specific tuning of neurons in human superior temporal gyrus. Cereb Cortex 24(10):2679–2693. PubMedCrossRefGoogle Scholar
  10. Cipolotti L, Butterworth B (1995) Toward a multiroute model of number processing: impaired number transcoding with preserved calculation skills. J Exp Psychol Gen 124(4):375. CrossRefGoogle Scholar
  11. Cohen L, Dehaene S, Naccache L, Lehéricy S, Dehaene-Lambertz G, Hénaff MA, Michel F (2000) The visual word form area: spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients. Brain 123(2):291–307. PubMedCrossRefGoogle Scholar
  12. Corbetta M, Shulman GL (2002) Control of goal-directed and stimulus-driven attention in the brain. Nat Rev Neurosci 3(3):215–229. CrossRefGoogle Scholar
  13. Cui X, Bray S, Reiss AL (2010) Functional near infrared spectroscopy (NIRS) signal improvement based on negative correlation between oxygenated and deoxygenated hemoglobin dynamics. NeuroImage 49(4):3039–3046. PubMedCrossRefGoogle Scholar
  14. Dehaene S (2011) The number sense: how the mind creates mathematics, 2nd edn. Oxford University Press, Oxford. Google Scholar
  15. Dehaene S, Akhavein R (1995) Attention, automaticity, and levels of representation in number processing. J Exp Psychol Learn Mem Cogn 21(2):314–326. PubMedCrossRefGoogle Scholar
  16. Dehaene S, Cohen L (1995) Towards an anatomical and functional model of number processing. Math Cogn 1(1):83–120Google Scholar
  17. Dehaene S, Dehaene-Lambertz G (2016) Is the brain prewired for letters? Nat Neurosci 19(9):1192–1193. PubMedCrossRefGoogle Scholar
  18. Dehaene S, Piazza M, Pinel P, Cohen L (2003) Three parietal circuits for number processing. Cogn Neuropsychol 20(3–6):487–506. PubMedCrossRefGoogle Scholar
  19. Ester EF, Sprague TC, Serences JT (2015) Parietal and frontal cortex encode stimulus-specific mnemonic representations during visual working memory. Neuron 87(4):893–905. PubMedPubMedCentralCrossRefGoogle Scholar
  20. Frankland SM, Greene JD (2015) An architecture for encoding sentence meaning in left mid-superior temporal cortex. Proc Natl Acad Sci 112(37):11732–11737. PubMedPubMedCentralCrossRefGoogle Scholar
  21. Friederici AD (2011) The brain basis of language processing: from structure to function. Physiol Rev 91(4):1357–1392. PubMedCrossRefGoogle Scholar
  22. Fulbright RK, Manson SC, Skudlarski P, Lacadie CM, Gore JC (2003) Quantity determination and the distance effect with letters, numbers, and shapes: a functional MR imaging study of number processing. Am J Neuroradiol 24(2):193–200PubMedGoogle Scholar
  23. Grotheer M, Herrmann K-H, Kovacs G (2016) Neuroimaging evidence of a bilateral representation for visually presented numbers. J Neurosci 36(1):88–97. PubMedCrossRefGoogle Scholar
  24. Hampshire A, Chamberlain SR, Monti MM, Duncan J, Owen AM (2010) The role of the right inferior frontal gyrus: inhibition and attentional control. NeuroImage 50(3):1313–1319. PubMedPubMedCentralCrossRefGoogle Scholar
  25. Hannagan T, Amedi A, Cohen L, Dehaene-Lambertz G, Dehaene S (2015) Origins of the specialization for letters and numbers in ventral occipitotemporal cortex. Trends Cogn Sci 19(7):374–382. PubMedCrossRefGoogle Scholar
  26. Holm S (1979) A simple sequentially rejective multiple test procedure. Scand J Stat 6(2):65–70. Google Scholar
  27. James KH, Gauthier I (2006) Letter processing automatically recruits a sensory–motor brain network. Neuropsychologia 44(14):2937–2949. PubMedCrossRefGoogle Scholar
  28. Japee S, Holiday K, Satyshur MD, Mukai I, Ungerleider LG (2015) A role of right middle frontal gyrus in reorienting of attention: a case study. Front Syst Neurosci 9:23. PubMedPubMedCentralCrossRefGoogle Scholar
  29. Joseph JE, Cerullo MA, Farley AB, Steinmetz NA, Mier CR (2006) fMRI correlates of cortical specialization and generalization for letter processing. NeuroImage 32(2):806–820. PubMedCrossRefGoogle Scholar
  30. Katzev M, Tuscher O, Hennig J, Weiller C, Kaller CP (2013) Revisiting the Functional specialization of left inferior frontal gyrus in phonological and semantic fluency: the crucial role of task demands and individual ability. J Neurosci 33(18):7837–7845. PubMedCrossRefGoogle Scholar
  31. Kaufmann L, Wood G, Rubinsten O, Henik A (2011) Meta-analyses of developmental fMRI studies investigating typical and atypical trajectories of number processing and calculation. Dev Neuropsychol 36(6):763–787. PubMedCrossRefGoogle Scholar
  32. Klein E, Moeller K, Nuerk H-C, Willmes K (2010) On the neuro-cognitive foundations of basic auditory number processing: an fMRI study. Behav Brain Funct 6:42. PubMedPubMedCentralCrossRefGoogle Scholar
  33. Klein E, Willmes K, Jung S, Huber S, Braga LW, Moeller K (2016) Differing connectivity of Exner’s area for numbers and letters. Front Hum Neurosci 10:281. PubMedPubMedCentralCrossRefGoogle Scholar
  34. Knops A, Nuerk H-C, Fimm B, Vohn R, Willmes K (2006) A special role for numbers in working memory? An fMRI study. Neuroimage 29(1):1–14. PubMedCrossRefGoogle Scholar
  35. Kruschke JK (2013) Bayesian estimation supersedes the t test. J Exp Psychol 142(2):573–588. CrossRefGoogle Scholar
  36. Liu C-L, Hue C-W, Chen C-C, Chuang K-H, Liang K-C, Wang Y-H, Wu CW, Chen J-H (2006) Dissociated roles of the middle frontal gyri in the processing of Chinese characters. Neuroreport 17(13):1397–1401. PubMedCrossRefGoogle Scholar
  37. McCloskey M, Schubert T (2014) Shared versus separate processes for letter and digit identification. Cogn Neuropsychol 31(5–6):437–460. PubMedCrossRefGoogle Scholar
  38. Menon V, Rivera SM, White CD, Glover GH, Reiss AL (2000) Dissociating prefrontal and parietal cortex activation during arithmetic processing. Neuroimage 12(4):357–365. PubMedCrossRefGoogle Scholar
  39. Park J, Hebrank A, Polk TA, Park DC (2012) Neural disocciation of number and letter recognition and its relationship to parietal numerical processing. J Cogn Neurosci 24(1):39–50. PubMedCrossRefGoogle Scholar
  40. Pernet C, Celsis P, Démonet J-F (2005) Selective response to letter categorization within the left fusiform gyrus. NeuroImage 28(3):738–744. PubMedCrossRefGoogle Scholar
  41. Polk TA, Stallcup M, Aguirre GK, Alsop DC, D’esposito M, Detre JA, Farah MJ (2002) Neural specialization for letter recognition. J Cogn Neurosci 14(2):145–159. PubMedCrossRefGoogle Scholar
  42. Reilhac C, Peyrin C, Démonet J-F, Valdois S (2013) Role of the superior parietal lobules in letter-identity processing within strings: FMRI evidence from skilled and dyslexic readers. Neuropsychologia 51(4):601–612. PubMedCrossRefGoogle Scholar
  43. Rivera SM, Reiss AL, Eckert MA, Menon V (2005) Developmental changes in mental arithmetic: evidence for increased functional specialization in the left inferior parietal cortex. Cereb Cortex 15(11):1779–1790. PubMedCrossRefGoogle Scholar
  44. Rorden C, Brett M (2000) Stereotaxic display of brain lesions. Behav Neurol 12(4):191–200. PubMedCrossRefGoogle Scholar
  45. Roux FE, Lubrano V, Lauwers-Cances V, Giussani C, Démonet JF (2008) Cortical areas involved in Arabic number reading. Neurology 70(3):210–217. PubMedCrossRefGoogle Scholar
  46. Sasai S, Homae F, Watanabe H, Taga G (2011) Frequency-specific functional connectivity in the brain during resting state revealed by NIRS. NeuroImage 56(1):252–257. PubMedCrossRefGoogle Scholar
  47. Shum J, Hermes D, Foster BL, Dastjerdi M, Rangarajan V, Winawer J, Miller KJ, Parvizi J (2013) A brain area for visual numerals. J Neurosci 33(16):6709–6715. PubMedPubMedCentralCrossRefGoogle Scholar
  48. Singh AK, Okamoto M, Dan H, Jurcak V, Dan I (2005) Spatial registration of multichannel multi-subject fNIRS data to MNI space without MRI. NeuroImage 27(4):842–851. PubMedCrossRefGoogle Scholar
  49. Sokolowski HM, Fias W, Ononye BC, Ansari D (2017) Are numbers grounded in a general magnitude processing system? A functional neuroimaging meta-analysis. Neuropsychologia 105:50–69. PubMedCrossRefGoogle Scholar
  50. Soltanlou M, Artemenko C, Ehlis A-C, Huber S, Fallgatter AJ, Dresler T, Nuerk H-C (2018) Reduction but not shift in brain activation in arithmetic learning in children: a simultaneous fNIRS-EEG study. Sci Rep 8:1707. PubMedPubMedCentralCrossRefGoogle Scholar
  51. Starrfelt R, Behrmann M (2011) Number reading in pure alexia—A review. Neuropsychologia 49(9):2283–2298. PubMedCrossRefGoogle Scholar
  52. Tong Y, Frederick B (2010) Time lag dependent multimodal processing of concurrent fMRI and near-infrared spectroscopy (NIRS) data suggests a global circulatory origin for low-frequency oscillation signals in human brain. NeuroImage 53(2):553–564. PubMedPubMedCentralCrossRefGoogle Scholar
  53. Tsuzuki D, Jurcak V, Singh AK, Okamoto M, Watanabe E, Dan I (2007) Virtual spatial registration of stand-alone fNIRS data to MNI space. NeuroImage 34(4):1506–1518. PubMedCrossRefGoogle Scholar
  54. Tzourio-Mazoyer N, Landeau B, Papathanassiou D, Crivello F, Etard O, Delcroix N, Mazoyer B, Joliot M (2002) Automated anatomical labeling of activations in SPM using a macroscopic anatomical parcellation of the MNI MRI single-subject brain. NeuroImage 15(1):273–289. PubMedCrossRefGoogle Scholar
  55. Venkatraman V, Ansari D, Chee MW (2005) Neural correlates of symbolic and non-symbolic arithmetic. Neuropsychologia 43(5):744–753. PubMedCrossRefGoogle Scholar
  56. Yeo DJ, Wilkey ED, Price GR (2017) The search for the number form area: a functional neuroimaging meta-analysis. Neurosci Biobehav Rev 78:145–160. PubMedCrossRefGoogle Scholar
  57. Zhou X, Chen C, Zhang H, Xue G, Dong Q, Jin Z, Zhang L, Peng C, Zhao H, Guo Y, Jiang T, Chen C (2006) Neural substrates for forward and backward recitation of numbers and the alphabet: a close examination of the role of intraparietal sulcus and perisylvian areas. Brain Res 1099(1):109–120. PubMedCrossRefGoogle Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.LEAD Graduate School & Research NetworkUniversity of TübingenTübingenGermany
  2. 2.Department of PsychologyUniversity of TübingenTübingenGermany
  3. 3.School of PsychologyUniversity of GlasgowGlasgowUK
  4. 4.Graduate Training Centre of Neuroscience/IMPRS for Cognitive and Systems NeuroscienceTübingenGermany
  5. 5.Leibniz-Institut für WissensmedienTübingenGermany
  6. 6.Department of Psychiatry and PsychotherapyUniversity of TübingenTübingenGermany

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