Sequential Neural Processes in Abacus Mental Addition: An EEG and fMRI Case Study

15 Pages·2012·4.45 MB·English

Sequential Neural Processes in Abacus Mental Addition:
An EEG and fMRI Case Study
Yixuan Ku1,2*, Bo Hong2, Wenjing Zhou2, Mark Bodner3, Yong-Di Zhou4*
1TheKeyLabofBrainFunctionalGenomics(MOE),InstituteofCognitiveNeuroscience,SchoolofPsychologyandCognitiveScience,EastChinaNormalUniversity,
Shanghai,China,2DepartmentofBiomedicalEngineering,SchoolofMedicine,TsinghuaUniversity,Beijing,China,3MINDResearchInstitute,SantaAna,California,United
StatesofAmerica,4DepartmentofNeurosurgery,JohnsHopkinsUniversity,Baltimore,Maryland,UnitedStatesofAmerica
Abstract
Abacusexpertsareabletomentallycalculatemulti-digitnumbersrapidly.Somebehavioralandneuroimagingstudieshave
suggested a visuospatial and visuomotor strategy during abacus mental calculation. However, no study up to now has
attempted to dissociate temporally the visuospatial neural process from the visuomotor neural process during abacus
mentalcalculation.Inthepresentstudy,anabacusexpertperformedthementaladditiontasks(8-digitand4-digitaddends
presentedinvisualorauditorymodes)swiftlyandaccurately.The100%correctratesinthisexpert’staskperformancewere
significantly higher than those of ordinary subjects performing 1-digit and 2-digit addition tasks. ERPs, EEG source
localizations,andfMRIresultstakentogethersuggestedvisuospatialandvisuomotorprocessesweresequentiallyarranged
during the abacus mental addition with visual addends and could be dissociated from each other temporally. The
visuospatialtransformationofthenumbers,inwhichthesuperiorparietallobulewasmostlikelyinvolved,mightoccurfirst
(around380 ms)aftertheonsetofthestimuli.Thevisuomotorprocessing,inwhichthesuperior/middlefrontalgyriwere
mostlikelyinvolved,mightoccurlater(around440ms).Meanwhile,fMRIresultssuggestedthatneuralnetworksinvolvedin
the abacus mental addition with auditory stimuli were similar to those in the visual abacus mental addition. The most
prominently activated brain areas in both conditions included the bilateral superior parietal lobules (BA 7) and bilateral
middlefrontalgyri(BA6).Theseresultssuggestasupra-modalbrainnetworkinabacusmentaladdition,whichmaydevelop
from normalmental calculationnetworks.
Citation:KuY,HongB,ZhouW,BodnerM,ZhouY-D(2012)SequentialNeuralProcessesinAbacusMentalAddition:AnEEGandfMRICaseStudy.PLoSONE7(5):
e36410.doi:10.1371/journal.pone.0036410
Editor:Yu-FengZang,HangzhouNormalUniversity,China
ReceivedJanuary3,2012;AcceptedApril9,2012;PublishedMay4,2012
Copyright:(cid:1)2012Kuetal.Thisisanopen-accessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense,whichpermitsunrestricted
use,distribution,andreproductioninanymedium,providedtheoriginalauthorandsourcearecredited.
Funding:ThisworkwassupportedbytheNationalNaturalScienceFoundationofChina(31100742)andChinaPostdoctoralScienceFoundation(20100480615
and201104246).Thefundershadnoroleinstudydesign,datacollectionandanalysis,decisiontopublish,orpreparationofthemanuscript.
CompetingInterests:Theauthorshavedeclaredthatnocompetinginterestsexist.
*E-mail:[email protected](YK);[email protected](YDZ)
Introduction abacususers(butnotabacusexperts)movedtheirfingersasifthey
had been manipulating a real abacus, and prohibition of this
The abacus has been used in Asia since 1200 A.D. for rapid movement or interfering with finger-tapping impaired their
precisecalculation[1].Thedesignationof‘‘Abacusexperts’’refers performance[2].Itseemedthattherewasalsoa‘‘mentalabacus’’
to those who have an unusual capability of operating a physical in those trained-abacus users’ minds. In addition, Hatano and
abacus for calculation, as well as calculating mentally with an Osawa demonstrated that inperformance of adelayed match-to-
abacus in mind through long-time training [2]. They can swiftly sample task, abacus experts could remember a sequence of 16-
and accuratelyperformmental addition with largenumbers. digitsforwardor14digitsbackward,whichwereusedasstimuliin
There are substantial studies on the neural mechanisms of thetask[14].Thedigitmemoryoftheexpertswasmoreinterfered
mental calculation for average people [3,4,5,6,7,8]. Some of the with concurrent visual-spatial tasks than with aural-verbal tasks
studieshavesupportedacognitivemodelinwhichthenumbersin [14].Performanceinmentalarithmetictasksoftheexpertswasalso
mental arithmetichave tworepresentational systems: a language- more affected by presentation of abacus images than by human
based system to store tables of exact arithmetic knowledge, and facesordigitnumbers[15].Allthosebehavioralstudies,together
a language-independent system for quantity manipulation and with several neuroimaging studies [16,17,18], suggested a visuos-
approximation, which relies on visuospatial networks [5]. Others patial representation of numbers, which had been developed
have however suggested that the basic numerical calculation throughabacuspracticethatinvolvedvisuomotorprocessingunder
strategy is finger-counting based representation [8]. In addition, certain rules. It might be more efficient to mentally manipulate
anumberofneuroimagingstudiesonneuralnetworkshaveshown multi-digit numbers using a visuospatial representation than
thatparietalandfrontalareasarethemaincorticalareasinvolved asequentiallyorganizedphonologicalrepresentation[18].
in mental calculation for average people [5,8,9,10,11,12]. However, none of the above studies had attempted to
Nevertheless, none of those studies is able to explain the dissociate the sequential neural processes, one from another,
extraordinary capabilityof mental calculation forabacus experts. during abacus mental calculation. We thus designed mental
Early behavioral studies suggested that a ‘‘mental abacus’’ was addition experiments (see figure 1A and 1B), in which we
used by abacus experts [13]. During mental calculation, trained- recorded electroencephalographic (EEG) signals from an abacus
PLoSONE | www.plosone.org 1 May2012 | Volume 7 | Issue 5 | e36410
EEGandfMRICaseStudyonAbacusMentalAddition
expert performing mental addition tasks, in an attempt to and her parents gave written informed consents before the
examine the temporally sequential processes for mental addition. experiment.
Furthermore, we measured the subject’s brain activities with
functional magnetic resonance imaging (fMRI) when the subject Behavioral Tasks for EEG Recording
was performing the same tasks, in order to explore the neural The EEG experiment was conducted in a dark, sound-proof
network underlying those processes. We hypothesized that there room, free of ambient electromagnetic interference. The subject
would be sequential visuospatial and visuomotor processes was placed in a comfortable chair facing an LED screen at eye
during abacus mental addition, in which both parietal and level with two speakers, one on each side of the screen, while
frontal cortical areas would be involved. performingthetasks.Sixdifferenttasks(labeledV-8,V-4,V-C,A-
8, A-4, and A-C, see descriptions later) were used in this study.
Methods Three of them (V-8, V-4, and V-C) were visual tasks, while the
other three (A-8, A-4, and A-C) were auditory tasks. The
The protocol of the experiment was approved by the
experiment is illustrated in figure 1A and 1B. In the visual tasks,
institutionalethicscommitteeintheSchoolofMedicine,Tsinghua
10numbers(formentaladdition)or10pseudo-words(forcontrol)
University. One abacus expert (female, age 16), who was one of
weredisplayedonebyonesequentiallyinthecenterofthescreen
the top performers in the World Mental Calculation Competi-
in each experimental run. In the auditory tasks, 10 numbers (or
tions, participated in the experiment as the subject. The subject
pseudo-words) were pronounced also one by one sequentially
Figure1.Demonstrationofexperimentalrunsinvisualandauditorytasks.Invisualtasks,thevisualstimulicouldbe8-digitnumbers,4-
digitnumbersor4-letterpseudo-words.Likewise,inauditorytasks,theauditorystimulicouldalsobe8-digitnumbers,4-digitnumbersor4-letter
pseudo-words.
doi:10.1371/journal.pone.0036410.g001
PLoSONE | www.plosone.org 2 May2012 | Volume 7 | Issue 5 | e36410
EEGandfMRICaseStudyonAbacusMentalAddition
Figure2.ERPresultsoftheEEGexperiments.(A)GrandaverageofERPsinvisualtasks.Themostprominentpeaksarenamed.(B)EEGelectrode
arrangements.Nineregionsofinterest(ROI)aredisplayedwiththenineframes.Theresultsofpost-hocTukeyHSDtestontheamplitudesofP2(C),
LPC-1(D,E),andLPC-2(F).
doi:10.1371/journal.pone.0036410.g002
PLoSONE | www.plosone.org 3 May2012 | Volume 7 | Issue 5 | e36410
EEGandfMRICaseStudyonAbacusMentalAddition
Table1. Behavioralresults from theabacus expert Table2.Statistical results ofthethree ERP components
performing the mentaladditiontasks (8-digit and4-digit (*p,0.05; **p,0.01;*** p,0.001).
addition),aswell astheaverage subjects performing the
mentaladditiontasks (2-digit and1-digit addition).
LPC1 LPC2
P2(170,210ms) (360,400ms) (420,460ms)
Average Amplitude
subjects Task V-2 V-1 A-2 A-1
TASK F(2,513)=20.97*** F(2,513)=20.03*** F(2,513)=39.19***
AR(%) 77.062.5 98.060.6 66.363.8 96.360.9
AP F(2,513)=46.45*** F(2,513)=416.06*** F(2,513)=510.03***
RT(s) 1.9560.14 1.1260.07 2.3060.18 1.3260.14
LR F(2,513)=9.20*** F(2,513)=10.08*** F(2,513)=4.64*
Abacusexpert Task V-8 V-4 A-8 A-4
TASK*AP F(4,513)=2.64* F(4,513)=4.24** NS
AR(%) 100 100 100 100
TASK*LR NS F(4,513)=2.56* F(4,513)=3.20*
RT(s) 1.8660.69 1.6560.81 2.4160.91 1.7660.73
AP*LR NS F(4,513)=13.61*** F(4,513)=8.75***
doi:10.1371/journal.pone.0036410.t001 TASK*AP*LR NS NS NS
Latency
throughspeakers.Thedurationofeachstimuluswasonesecond, TASK F(2,513)=5.80** F(2,513)=3.90* NS
andtheintervalbetweenstimulusonsetswastwoseconds.Invisual
AP F(2,513)=27.00*** NS NS
tasks, 8-digit numbers (V-8), 4-digit numbers (V-4) and 4-letter
LR F(2,513)=23.60*** NS F(2,513)=4.20*
pseudo-words (V-C) were presented. In the A-8 task, the 1-s
duration of the stimulus was equally divided into eight segments TASK*AP NS NS NS
(125 msforeach).Eachsegmentstartedwithanoralpresentation TASK*LR NS F(4,513)=3.80** NS
ofadigit(inChinese).Thisdigitwasrandomlyselectedfromnine AP*LR F(4,513)=8.00*** NS NS
digits (1to 9)recorded by a male andits duration was artificially
TASK*AP*LR NS NS NS
compressedinto100ms.InA-4andA-Ctasks,the1-sdurationof
the stimulus was equally divided into four segments (250 ms for doi:10.1371/journal.pone.0036410.t002
each). Eachsegment started withan orally presented digitlasting
for230msinA-4,andaletterlastingfor230msinA-C.Inboth (Compumedics, US). Afterwards, the 60 channel EEG data
tasks, the digits and letters were also recorded by a male and were analyzed using Matlab 7.0 (Math Works, US) and
artificiallycompressedinto230ms.Thesubjectwasinstructedto EEGLAB 6.0 toolbox (Swartz Center for Computational
maintainfocusonthecenterofthescreeninthevisualtasks.Inthe Neurosciences, US) [19]. Event-related potentials (ERPs) were
auditory tasks, a cross was presented in the center of the screen calculated by averaging the trials. The baseline was established
duringtheentireperiodofarun.Thesubjectwasrequiredtofix by averaging voltages from the 50ms preceding the onset of the
her sights on the cross. In the mental addition tasks, the subject stimulus and was subtracted from the ERPs. ERP components
wasrequiredtoaddthetennumberspresentedinsuccessionand were defined as peaks and troughs, and named as routines (P2,
thenselectthecorrectanswer(sum)fromthreeoptionspresented LPC-1, and LPC-2 as in figure 2A). The amplitude of an ERP
on the screen one second after the off-set of the last of those ten component was measured from its peak to the baseline (peak-
numbers, by pressing one of the corresponding buttons on value minus the baseline-value). The latency was measured from
a keyboard. In the control tasks, the subject was instructed to the stimulus onset to the peak.
randomlypressoneofthethreebuttonsonesecondaftertheoff-
setofthelastpseudo-word.Twentyrunswerecarriedoutforeach Statistical Analyses
task and were grouped into two blocks. The blocks of different Three-wayanalysisofvariance(ANOVA)wasusedtocompare
tasks were presented randomly. The interval between runs was ERP components (amplitude and latency). Since the offset of an
3,5seconds,andbetweenblocks,5,10minutes.Thesubjectwas auditory stimulus (an aurally-presented number, or word) could
instructed toavoidunnecessaryeyemovementsduringthewhole not be defined as accurately as the visual one, only visual ERP
task. components were included in statistical analysis. The electrodes
were grouped into 9 regions of interest (ROI) as indicated in
EEG Recording and Processing figure2B,andERPsfromelectrodesofeachregionwereaveraged
EEG signals were recorded by an EEG recording system across electrodes to improve signal-to-noise-ratio. The ANOVA
(SynAmps2, Compumedics, Ltd Corp, US). Sixty Ag-AgCl scalp factors were TASK (V-8, V-4 and V-C), AP (frontal-central,
electrodes (Quick-Caps, Neuroscan) were arranged in a standard central-parietal and parietal-occipital), and LR (left, medial and
10–20 system (figure 2B). EEG signals from each electrode were right). All ERP statistical analyses were performed with Statistica
referenced to linked earlobes. Two linked electrodes were placed (StatSoft, US).
ontheearlobes(oneoneachearlobe).Thesignalfromthelinked
earlobeelectrodesservedasthereference.Theimpedanceofeach sLORETA Analyses
electrode was kept below 5 kV during the experiment. Addition- Brain generators associated with modulation of ERPs were
ally, the electro-oculogram (EOG) signal was recorded to detect estimated by standardized low resolution brain electromagnetic
horizontal and vertical eye movements. EEG (60 electrodes) and tomographic analysis (sLORETA). The current density was
EOG (2 bipolar electrodes) signals were filtered (0.1–100Hz represented in 3-D Tailarach space of the scalp-recorded
band-pass),amplified,digitized(1000Hzsamplerate),andstored electrical activity using the sLORETA software package [20].
for off-lineanalysis. sLORETA was used to provide an approximate three-di-
EOG contamination in EEG was excluded by means of mensional solution of the EEG inverse problem, aiming to
linear regression implemented in Neuroscan EDIT software determine the most active brain regions in a given instant of
PLoSONE | www.plosone.org 4 May2012 | Volume 7 | Issue 5 | e36410
EEGandfMRICaseStudyonAbacusMentalAddition
Figure3.SourcelocalizationofP2component.(A)sLORETAresultsofthesubtractionofP2tracesbetweenV-CandV-4.(B)sLORETAresultsof
thesubtractionofP2tracesbetweenV-CandV-8.
doi:10.1371/journal.pone.0036410.g003
PLoSONE | www.plosone.org 5 May2012 | Volume 7 | Issue 5 | e36410
EEGandfMRICaseStudyonAbacusMentalAddition
Figure4.SourcelocalizationofLPC-1component.(A)sLORETAresultsofthesubtractionofLPC-1tracesbetweenV-4andV-C.(B)sLORETA
resultsofthesubtractionofLPC-1tracesbetweenV-8andV-C.
doi:10.1371/journal.pone.0036410.g004
PLoSONE | www.plosone.org 6 May2012 | Volume 7 | Issue 5 | e36410
EEGandfMRICaseStudyonAbacusMentalAddition
Figure5.SourcelocalizationofLPC-2component.(A)sLORETAresultsofthesubtractionofLPC-2tracesbetweenV-4andV-C.(B)sLORETA
resultsofthesubtractionofLPC-2tracesbetweenV-8andV-C.
doi:10.1371/journal.pone.0036410.g005
PLoSONE | www.plosone.org 7 May2012 | Volume 7 | Issue 5 | e36410
EEGandfMRICaseStudyonAbacusMentalAddition
Table3. Thebrainareas activated in4-digitvisual mental addition,incontrast to thevisual controltask (family-wise-error
correctedp,0.001).
AnatomicalLocalization Coordinates Cluster(Voxels) Z-Value
X(mm) Y(mm) Z(mm)
SuperiorParietalLobule BA7 222 270 60 577 11.34
BA7 232 252 56 11.17
SuperiorParietalLobule BA7 18 264 52 676 9.46
BA7 34 246 48 8.89
BA7 36 254 52 7.98
MiddleFrontalGyrus BA6 26 24 50 135 8.45
MiddleFrontalGyrus BA6 222 214 54 147 8.11
InferiorParietalLobule BA40 42 228 40 86 7.87
InferiorParietalLobule BA40 250 240 50 60 6.98
InferiorFrontalGyrus BA9 258 14 28 54 6.79
PrecentralGyrus BA4 254 214 26 47 6.67
InferiorFrontalGyrus BA45 54 14 20 38 5.82
doi:10.1371/journal.pone.0036410.t003
time. This analysis was based on the measurements of a dense Functional volumes were analyzed by using Statistical Para-
grid of electrodes, which were placed on the entire scalp surface metric Mapping 5 (SPM5; www.fil.ion.ucl.ac.uk/spm/software/
covering the brain [20]. spm5) implemented in MATLAB. Motion correction to the first
sLORETA was used to estimate the current source density functional scan was performed using a six-parameter rigid-body
distributionforepochsofbrainelectricalactivityonadensegridof transformation [22]. The motion corrected images were
6239voxelsat5 mmspatialresolution.Threeperiodsweretaken normalized to the Montreal Neurological Institute (MNI)
for analysis according to the three prominent ERP components: coordinate system, and spatially smoothed with a 6-mm full-
P2, 170–210ms; LPC-1, 360–400 ms; LPC-2, 420–460ms. The width-at-half-maximum-isotropic Gaussian kernel. Statistical
difference in ERP waveform between the addition task and the fMRI analysis was performed using the general linear model
control taskwere submitted forsLORETA[21]. (GLM), as implemented in SPM5. Next, we created contrast
images for each stimulus between the mental addition task and
fMRI Experiments and Data Analyses the control task. Family-wise-error (FWE) was corrected for
multiple spatial comparisons. Clusters with more than 10
ThefMRIexperimentwascarriedoutinsideathree-TeslaMR
contiguous supra-threshold (FWE p,0.05) voxels were shown
scanner (Siemens Trio) in the Institute of Biophysics, Chinese
in activation tables.
Academy of Science. A high resolution T1-weighted multi-sliced
anatomicalimagewasacquiredinthesagitalorientation,usinga3D
Results
gradient echo sequence (pulse repetition=2530ms; echo
time=3.37 ms; inversion time=1100; number of signals aver-
Behavioral Results
aged=1; matrix size=25662566190), for the reference of func-
Behavioralresultsoftheabacusexpertwasrecordedandlisted
tional images. Multi-sliced T2*-weighted fMRI images were
(table1)togetherwiththeresultsofourpreviousstudy[23]from
obtained with a gradient echo-planar sequence using axial slice
averagesubjectswhoperformedadditiontaskswithfewerdigits(1-
orientation (25 slices; voxel size=3.44 mm63.44mm65mm;
digit and 2-digit). In all addition tasks, the expert made 100
matrix size=64664625; TR=2000ms; TE=30ms; flip an-
percent correct choices. The 100% accuracy of the expert was
gle=90u).Thesubjectwasscannedwhileperformingthetask,lying
overthreestandarddeviationsawayfromthemeancorrectrateof
in the scanner and faced with an LED screen where task images
theaverage subjects ineach taskasgivenin table1.
(numbers,pseudo-words,andinstructions)wereprojectedwithan
opticalfiber.Thevisualanglewas0.6degreeforeachdigitorletterin
ERP Results
thestimulus.Auditorystimuliwerepresentedthroughanair-driven
Averaged event related potentials (ERPs) along the midline
earphonesystem.Thesubjectselectedthecorrectanswerbypressing
electrodes were shown in figure 2A. The three separated ERP
oneofthethreebuttonsinabuttoncase.ThetasksusedinthefMRI
components were P2 (peaked around 190ms), LPC1 (peaked
experimentwereidenticaltothoseintheEEGexperiment.ThefMRI
around 380ms), and LPC2 (peaked around 440ms). ANOVA
experiment for the subject included four sessions, each of them
results of these ERPs are shown in table 2. Task conditions
containingsixtaskblocks(correspondingtosixtasksrespectively:V-8,
(TASK:V-8,V-4,V-C)exertedsignificanteffectsonamplitudesof
V-4, V-C, A-8, A-4, and A-C) that were arranged in a random
all the three ERP components, as well as AP (frontal-central,
sequence.Eachofthoseblocksincludedtwoexperimentalruns,and
central-parietal and parietal-occipital) and LR (left, middle, and
eachrunconsistedof10stimuli,correspondingto10MRIscans.
right) factors. The TASK*AP interaction was significant for the
Therefore,eachofthesixtaskscontained80scansintotal.Thesubject
amplitudes of P2 and LPC-1. The TASK*LR interaction was
tookarestof10secondsbetweenblocksandarestof3–5minutes
significantfortheamplitudesofLPC-1andLPC-2.Resultsofthe
betweensessions.
post-hoc TukeyHSDtest ontheamplitudes ofERP components
PLoSONE | www.plosone.org 8 May2012 | Volume 7 | Issue 5 | e36410
EEGandfMRICaseStudyonAbacusMentalAddition
sLORETA Results
sLORETA was applied to subtractions of ERP traces [21]
betweentheadditiontaskandthecontroltask.Timewindowsfor
the analysis were the periods of the three ERP components (P2,
LPC-1 and LPC-2). The sLORETA results of these components
were shown in figures 3, 4, and 5 respectively. Cortical areas
showing maximal activity were observed as follows: around
190ms (P2), the most active area was located in the left middle
temporalgyrus(BA21)forsubtractionsbetweenV-CandV-8/V-
4 (figure 3); around 380ms (LPC-1), the most active areas were
locatedinbilateralsuperiorparietallobules(BA7)andprecuneus
(BA 7) for subtractions between V-8/V-4 and V-C (figure 4);
around440ms(LPC-2),forasubtractionbetweenV-4andV-C,
themostactiveareawaslocatedintheleftmiddletemporalgyrus
(BA 21), and for a subtraction between V-8 and V-C, the most
active areas were located in bilateral superior frontal gyri (BA 8)
andbilateral middle frontalgyri (BA6) (figure 5).
fMRI Results
Brain activation of V-4 in contrast to V-C (abbreviation, V4/
VC) is shown in table 3 and figure 6A. The most active areas
include bilateral superior parietal lobules (BA 7) (cluster size: left
577 volumes, right 676 volumes; FWE p,0.001) and bilateral
middle frontal gyri (BA 6) (cluster size: left 147 volumes, right 135
volumes;FWEp,0.001).BrainactivationofV-8incontrasttoV-
C (abbreviation, V8/VC) isshown intable 4 and figure 6B. The
most active areas also include bilateral superior parietal lobules
(BA 7) (cluster size: left 835 volumes, right 916 volumes; FWE
p,0.001)andbilateralmiddlefrontalgyri(BA6)(clustersize:left
362 volumes, right 278 volumes; FWE p,0.001), and the
corresponding active cluster sizes are larger than those in table 3
andfigure 6A.
Brain activation of A-4 in contrast to A-C (abbreviation, A4/
AC) is shown in table 5 and figure 7A. The most active areas
include bilateral superior parietal lobules (BA 7) (cluster size: left
398 volumes, right 421 volumes; FWE p,0.001) and bilateral
middle frontal gyri (BA 6) (cluster size: left 100 volumes, right 77
volumes;FWEp,0.001).BrainactivationofA-8incontrasttoA-
C (abbreviation, A8/AC) is shown in table 6 and figure 7B. The
most active areas also include bilateral superior parietal lobules
(BA 7) (cluster size: left 1308 volumes, right 1763 volumes; FWE
p,0.001)andbilateralmiddlefrontalgyri(BA6)(clustersize:left
513 volumes, right 422 volumes; FWE p,0.001), and the
corresponding active cluster sizes are larger than those in table 5
andfigure 7A.
Figure 6. fMRI results in visual mental addition. (A) Glass-brain Brain activation of V-8 in contrast to V-4 yields no significant
viewsoffMRIactivatedareasofV-4vs.V-C(p,0.05,family-wise-error (FWEp,0.05)results.BrainactivationofA-8incontrasttoA-4is
corrected). Talairach coordinates of the activated points are listed in shownintable7andfigure8A.Themostprominentactivationis
table 3. (B) Glass-brain views of fMRI activated areas of V-8 vs. V-C
observed in left inferior frontal gyrus (BA 44) (cluster size=137
(p,0.05, family-wise-error corrected). Talairach coordinates of the
volumes, FWE p,0.001).
activatedpointsarelistedintable4.
doi:10.1371/journal.pone.0036410.g006 TheconjunctionofbrainactivationsbetweenV4/VCandA4/
ACisshowninfigure8B,whichisasubsetoftheconjunctionof
brain activations between V8/VC and A8/AC (figure 8C). The
(P2, LPC-1, LPC-2) are shown in figures 2C–2F. The P2
mostprominentconjunctionactivationsbetweenV4/VCandA4/
amplitude was significantly larger in V-C than that in V-8 and
AC are observed in bilateral superior parietal lobules (BA 7)
V-4 at parietal-occipital recording sites (figure 2C). The LPC-1
(cluster size: left 388 volumes, right 403 volumes; FWE p,0.001)
amplitudeinV-8wassignificantlylargerthanthoseinV-4andV-
and bilateral middle frontal gyri (BA 6) (cluster size: left 90
C at middle frontal-central and central-parietal recording sites
volumes, right76volumes; FWE p,0.001).
(figures2Dand2E).ThedifferencebetweenV-8andV-CinLPC-
Brain activation of V4/VC in contrast to A4/AC yields no
1intherightrecordingsiteswasnearsignificance(p=0.058).The
significant (FWE p,0.05) results. Brain activation of A8/AC in
LPC-2amplitudeinV-8andV-4wassignificantlylargerthanthat
contrast to V8/VC is shown in table 8 and figure 8D. The most
in V-C at middle recording sites. Meanwhile, the LPC-2
prominent activations are observed in left superior frontal gyrus
amplitudeinV-8waslargerthanthatinV-4atmiddleandright
(BA6)(clustersize=151volumes,FWEp,0.001),leftsupramar-
recording sites (figure 2F).
ginal gyrus (BA40) (cluster size=221 volumes, FWE p,0.001),
PLoSONE | www.plosone.org 9 May2012 | Volume 7 | Issue 5 | e36410
EEGandfMRICaseStudyonAbacusMentalAddition
Table4. Thebrainareas activated in8-digitvisual mental addition,incontrast to thevisual controltask (family-wise-error
correctedp,0.001).
AnatomicalLocalization Coordinates Cluster(Voxels) Z-Value
X(mm) Y(mm) Z(mm)
SuperiorParietalLobule BA7 222 270 60 835 13.95
BA7 230 252 56 12.38
BA7 224 262 58 11.1
SuperiorParietalLobule BA7 16 264 54 916 13.1
BA7 32 246 48 10.15
BA7 26 252 52 9.5
Sub-Gyral BA6 26 24 52 278 12.34
InferiorParietalLobule BA40 42 228 40 253 9.57
BA2 52 226 50 7.02
MiddleFrontalGyrus BA6 222 214 56 362 9.19
BA6 224 22 64 8.16
BA6 216 22 56 6.93
MiddleFrontalGyrus BA9 256 16 30 74 7.93
InferiorParietalLobule BA40 252 238 50 81 7.22
BA40 256 232 44 5.74
PostcentralGyrus BA2 254 218 30 21 5.65
doi:10.1371/journal.pone.0036410.t004
and left inferior frontal gyrus (BA44) (cluster size=187 volumes, is because of years of training in abacus calculation that the
FWE p,0.001). expert can perform those tasks quickly and accurately, which
are very difficult for average people.
Discussion
Sequential Processes During Abacus Mental Addition
Behavioral Results
The most significant difference observed between the mental
In the current study, the abacus expert performed the
additiontaskandthecontroltaskwasintheERPcomponents(P2,
addition tasks with multi-digit (8-digit and 4-digit) numbers
LPC-1andLPC-2).P2hasbeenconsideredtobeanERPindexof
swiftly and accurately. Her accuracy rates (100%) were
taskrelevanceevaluationofvisualstimuli[25].Fromthispointof
significantly higher than those of the average subjects perform-
view, theP2 in the addition task should be different from that in
ing analogous 1-digit and 2-digit addition tasks. The accuracy of
the control task. Indeed, the P2 amplitude in the addition
the average people performing addition tasks dropped as the
condition was significantly lower than that in the control
addends got larger (more digits in the tasks), which dropped to
condition. The source of the difference was located most
almost zero as the addends reached 4-digits [24]. Apparently, it
Table5.Thebrainareasactivatedin4-digitauditorymentaladdition,incontrasttotheauditorycontroltask(family-wise-error
correctedp,0.001).
AnatomicalLocalization Coordinates Cluster(Voxels) Z-Value
X(mm) Y(mm) Z(mm)
SuperiorParietalLobule BA7 222 270 60 398 10.17
BA7 230 252 56 8.32
SuperiorParietalLobule BA7 18 262 50 421 9.48
BA7 34 246 48 6.94
BA7 34 254 54 6.43
MiddleFrontalGyrus BA6 26 24 50 77 7.09
PrecentralGyrus BA6 224 214 54 100 6.98
InferiorFrontalGyrus BA9 258 14 28 25 6.3
InferiorParietalLobule BA40 40 228 40 15 5.75
InferiorParietalLobule BA40 250 240 50 12 5.75
doi:10.1371/journal.pone.0036410.t005
PLoSONE | www.plosone.org 10 May2012 | Volume 7 | Issue 5 | e36410