Modulating Neuronal Activity Produces Specific and Long-Lasting Changes in Numerical Competence

Abstract

Around 20% of the population exhibits moderate to severe numerical disabilities [1Dowker A. Use of derived fact strategies by children with mathematical difficulties.Cogn. Dev. 2009; 24: 401-410Crossref Scopus (29) Google Scholar, 2Parsons S. Bynner J. Does Numeracy Matter More?. NRDC, London2005Google Scholar, 3Butterworth B. Developmental dyscalculia.in: Campbell J.I.D. Handbook of Mathematical Cognition. Psychology Press, New York2004: 455-467Google Scholar], and a further percentage loses its numerical competence during the lifespan as a result of stroke or degenerative diseases [4Willmes K. Chapter 17 acalculia.Handb Clin Neurol. 2008; 88: 339-358Crossref PubMed Scopus (14) Google Scholar]. In this work, we investigated the feasibility of using noninvasive stimulation to the parietal lobe during numerical learning to selectively improve numerical abilities. We used transcranial direct current stimulation (TDCS), a method that can selectively inhibit or excitate neuronal populations by modulating GABAergic (anodal stimulation) and glutamatergic (cathodal stimulation) activity [5Stagg C.J. Best J.G. Stephenson M.C. O'Shea J. Wylezinska M. Kincses Z.T. Morris P.G. Matthews P.M. Johansen-Berg H. Polarity-sensitive modulation of cortical neurotransmitters by transcranial stimulation.J. Neurosci. 2009; 29: 5202-5206Crossref PubMed Scopus (653) Google Scholar, 6Utz K.S. Dimova V. Oppenländer K. Kerkhoff G. Electrified minds: Transcranial direct current stimulation (tDCS) and galvanic vestibular stimulation (GVS) as methods of non-invasive brain stimulation in neuropsychology—a review of current data and future implications.Neuropsychologia. 2010; 48: 2789-2810Crossref PubMed Scopus (352) Google Scholar]. We trained subjects for 6 days with artificial numerical symbols, during which we applied concurrent TDCS to the parietal lobes. The polarity of the brain stimulation specifically enhanced or impaired the acquisition of automatic number processing and the mapping of number into space, both important indices of numerical proficiency [7Rubinsten O. Henik A. Developmental dyscalculia: Heterogeneity might not mean different mechanisms.Trends Cogn. Sci. 2009; 13: 92-99Abstract Full Text Full Text PDF PubMed Scopus (179) Google Scholar, 8Booth J.L. Siegler R.S. Numerical magnitude representations influence arithmetic learning.Child Dev. 2008; 79: 1016-1031Crossref PubMed Scopus (398) Google Scholar, 9Dehaene S. Izard V. Spelke E. Pica P. Log or linear? Distinct intuitions of the number scale in Western and Amazonian indigene cultures.Science. 2008; 320: 1217-1220Crossref PubMed Scopus (416) Google Scholar]. The improvement was still present 6 months after the training. Control tasks revealed that the effect of brain stimulation was specific to the representation of artificial numerical symbols. The specificity and longevity of TDCS on numerical abilities establishes TDCS as a realistic tool for intervention in cases of atypical numerical development or loss of numerical abilities because of stroke or degenerative illnesses.