Brazilian
Journal
of
OTORHINOLARYNGOLOGY
www.bjorl.org
ORIGINAL
ARTICLE
Cortical
inhibition
effect
in
musicians
and
non-musicians
using
P300
with
and
without
contralateral
stimulation
夽
,
夽夽
Camila
Maia
Rabelo
∗,
Ivone
Ferreira
Neves-Lobo,
Caroline
Nunes
Rocha-Muniz,
Thalita
Ubiali,
Eliane
Schochat
DepartamentofPhysiotherapy,SpeechandLanguageTherapy,FaculdadedeMedicina,UniversidadedeSãoPaulo(FMUSP), SãoPaulo,SP,Brazil
Received25July2013;accepted22July2014 Availableonline21November2014
KEYWORDS
Electrophysiology; Event-related potentials,P300; Hearing;
Music
Abstract
Introduction:Musicians havemore robustandefficientneuralresponses inthecortical and sub-cortical regions, demonstratingthatmusicalexperiencebenefits theprocessing ofboth non-linguisticandlinguisticstimuli.
Objective: ThisstudyaimedtoverifyP300’slatencyandamplitudebehavioralusing contralat-eralstimulationinmusiciansandnon-musicians.
Methods:Thiswasacase---controlstudy.Subjectsweredividedintwogroups:musicians, com-prising30professionalmusicians,andnon-musicians,comprising25subjectswithoutmusical experience.
Results:Thepresentstudyshowedthatthemusicianshadlowerlatenciesandhigher ampli-tudesthanthenon-musiciansintheP300withoutcontralateralnoise.FortheP300amplitude values, the difference between groups persisted,andthe musicians presentedsignificantly higher amplitudevaluescomparedwith thenon-musicians; additionally, theanalysis ofthe noiseeffectontheP300responseshowedthatthelatencyvaluesweresignificantlyincreased inthemusicians.
Conclusion: Thecentralauditorynervoussystemofmusicianspresentspeculiarcharacteristics ofelectrophysiologicalresponsesprobablyduetotheplasticityimposedbymusicalpractice. © 2014Associac¸ãoBrasileira de Otorrinolaringologiae CirurgiaCérvico-Facial. Publishedby ElsevierEditoraLtda.Allrightsreserved.
夽 Pleasecitethisarticleas:RabeloCM,Neves-LoboIF,Rocha-MunizCN,UbialiT,SchochatE.Corticalinhibitioneffectinmusiciansand
non-musiciansusingP300withandwithoutcontralateralstimulation.BrazJOtorhinolaryngol.2015;81:63---70.
夽夽
Institution:DepartamentofPhysiotherapy,SpeechandLanguageTherapy,FaculdadedeMedicina,UniversidadedeSãoPaulo(FMUSP), SãoPaulo,SP,Brazil.
∗Correspondingauthor.
E-mail:cmrabelo@gmail.com(C.M.Rabelo). http://dx.doi.org/10.1016/j.bjorl.2014.11.003
PALAVRAS-CHAVE
Eletrofisiologia; Potencialevocado P300;
Audic¸ão; Música
Efeitodainibic¸ãocorticalutilizandooP300emmúsicosenãomúsicoscomesem estimulac¸ãocontralateral
Resumo
Introduc¸ão:Osmúsicospossuemrespostasneuraismaisrobustaseeficientesemregiões corti-cais,mostrandoqueaexperiênciamusicalbeneficiaoprocessamentodeestímuloslinguísticos enãolinguísticos.
Objetivo:Verificar como alatênciae aamplitudedoP300se comportausandoestimulac¸ão contralateral,emmúsicosenãomúsicos.
Método: Estudodecaso-controle.Osindivíduosforamdivididosemdoisgrupos:GM(grupode músicos)com30músicosprofissionaiseGNM(grupodenão músicos)com25indivíduossem experiênciamusical.
Resultados: Osresultadosmostraramque:GMtevelatênciasmenoreseamplitudesmaioresdo queaGNMnoP300semruídocontralateral.ParaosvaloresdeamplitudedoP300,adiferenc¸a entreosgrupossemanteve,eoGMapresentouvaloresdeamplitudesignificativamentemaiores emcomparac¸ãocomoGNM;eaanálisedoefeitodoruídosobrearespostaP300mostrouque osvaloresdelatênciaforamsignificativamentemaioresnoGM.
Conclusão:Concluímosqueosistemanervosoauditivocentraldemúsicosapresenta caracterís-ticaspeculiaresde respostaseletrofisiológicasprovavelmentedevidoàplasticidadeimposta pelapráticamusical.
©2014Associac¸ãoBrasileira deOtorrinolaringologiaeCirurgiaCérvico-Facial.Publicadopor ElsevierEditoraLtda.Todososdireitosreservados.
Introduction
Theeffectsofmusicalexperienceontherepresentationof sounds in the auditory cortexhave been functionallyand anatomically observed in several studies. Anatomical dif-ferenceswerefoundinvariousbrainstructures,suchasthe Heschl’sgyrus, the secondary auditory cortex, the corpus callosum,andthetemporalplaneofmusicians.1
Astudyby Ohnishetal.in2001,usingfunctional mag-neticresonanceimaging(FMRI),demonstratedthatpassive musiclisteningproducessignificantactivationinthe supe-riortemporal and bilateral medial gyrus, together known asthe auditory association cortex, in both musicians and non-musicians.Musiciansshowrightdominanttemporal cor-ticalactivation,whereasnon-musiciansshowleftdominant temporalcorticalactivation.2
Chermak stated that, by stimulating different areas of the brain, such as the frontal, temporal, parietal, and sub-cortical regions, music can help improve several attention-related functions, including memory, learning, language,andevenemotionalaspects.3
Several authors also agree that musicians have more robust and efficient neural responses in the cortical and sub-corticalregions,demonstratingthatmusicalexperience benefits the processingof both non-linguistic and linguis-ticstimuli.Thus,musicaltraininghasbeenafrequentand effective resourcein the rehabilitation of communication disorders.3---5
Auditoryevokedpotentials(AEPs)areimportanttoolsin theinvestigationofauditoryfunctionbecause,inaddition tobeingobjectiveandnoninvasivetests,theyaresensitive toplasticchangesintheauditorypathwaythatresultfrom externalstimulation.6
P300 is an endogenous long-latency auditory evoked potential(LLAEP) that dependsontheconscious response of theindividualand appearsasa positivewave between 50 and 500ms after acoustic stimulus presentation, with amplituderangingfrom7to25V.Thispotentialiselicited
in an auditory discrimination task termed ‘‘the oddball paradigm’’, and is alsoknown asa cognitive potentialas it is used to investigate cognitive abilities, such as dis-crimination and attention. The P300 generators are still beinginvestigated,butitisknownthatP3isoriginatedby differentstructuresnotonlyinthecortex,butalsoin sub-cortical regions.Thus, itcan besaidthat P300comprises responses fromfrontal andcentro-parietalcortex, aswell asthehippocampus.7Thereareevidencesthatsubthalamus
andmedialgeniculatebodycontributestoP300generation, withsomeactivitiesattheorbitalgyrus,rostralthalamus, andanteriorcommissure.8,9Moreover,the current
investi-gationsregarding latepotentialsfocusontherelationship between their characteristics and informationprocessing, suchascodification,memory,anddecision-making.10
AEPstudieshaveshownthattheauditorycortexresponds to sounds differently in musicians and non-musicians,11,12
and that the auditory cortexplasticity, in relation to the effectsofmusicaltraining,ishigherwhenthetrainingbegins in childhood.2,13 In2003, Trainoretal. observed
improve-ment in LLAEPs after auditory musical training in both childrenandadults,showingthatmusiccanalterthe audi-tory cortical representation.13 Other authorssuggest that
this typeof stimulationcan be usedasa toolin auditory rehabilitation.3
musicians anda groupof non-musicians(NMG); the group ofmusicians(MG)presentedreducedlatenciesandgreater amplitudes.11
Musacchiaetal.,in2007,evaluatedthebrainstemAEPs inaMG,andobservedthattheyexhibitedreducedlatencies andlargeramplitudeswhencomparedwithaNMG,bothfor musicalandspeechstimuli.5
Even beyond sub-cortical and cortical functional enhancements, musical trainingmayshape auditory func-tion in structures that are as peripheral as the cochlea; musiciansdemonstratedagreater degreeof efferent con-troloverouterhaircellactivityalongthebasilarmembrane than non-musicians.14,15 Such comprehensive perceptual
andneuralenhancementsmaybedriven,atleastpartially, by strengthened cognitive control over basic auditory processing,as engenderedby auditory attention,16---18 two
auditorycognitiveskillsthatareenhancedinmusicians. Krishnamurti, in 2001, observed the influence of con-tralateralcompetitivenoiseinP300latencyandamplitude. According totheauthor, theintroduction of contralateral competitivenoisecomplicatesthesituation,increasingthe difficulty of P300discrimination and consequently result-ing in increased latency and decreased amplitude of this potential.19
Although behavioral studies have found similar effects in musicians and non-musicians,20 the results with
event-relatedpotentials(ERPs)areinconsistent.21
Previous studies have demonstrated the reduction of cochlear response --- decreased amplitude and increased latencies --- due toinhibitory effectinduced by the pres-enceof noise. These changesin responses wereobserved throughouttheauditorypathway,throughassessmentsfrom thecochleauptotheauditorycortex,22demonstratingthat
theauditorysystemofhealthyindividualssuffersinhibition effectsinthepresenceofacompetitivestimulus.
Moreover,littleisknownaboutthephysiological mecha-nismsthatunderliethefunctioningoftheefferentpathway. Toinvestigatethepositiveeffectofmusicalexperienceon theauditorypathway,thisstudyaimedtoassessthelatency andamplitudeofP300cognitivepotentialresponsesinthe presenceandabsenceofcontralateralnoiseinmusiciansand non-musicians.Thisstudyaddressedthefollowingresearch questions:Aretheredifferencesinthelatenciesand ampli-tudesofP300auditoryERPs,withandwithoutcontralateral noise,betweenmusiciansandnon-musicians?Can contralat-eralnoiseinhibitP300responseinbothgroups?
Methods
The present study wasconducted at theauthors’ laband wasapprovedbytheethicscommittee(No.0874/07).
Participants
Thiswasacase---controlstudythatincluded30professional musiciansofbothgenderswhohadformallystudiedmusic sincechildhoodorteenageyearsandstillpracticesomekind ofmusicalinstrument,between20and53yearsofage,who werereferredtoastheMG.Inthecontrolgroup,25subjects of both genders without any formal musical experience, between18 and30 yearsofage, wereselectedand were
referredtoastheNMG.Allparticipantssignedaninformed consent.
Asinclusioncriteria,itwasestablishedthatallofthe par-ticipantsshouldhavehearingthresholdswithinthenormal limitsat frequencies of250---8000Hz,23 which wasverified
throughpuretone audiometry,and an absenceofhearing complaints and/or neurological disorders. The difference betweenthegroupswasdeterminedbasedonyearsof musi-calexperience.
Theproceduresperformed intheNMGandMGincluded thefollowing: P300 withandwithout contralateralnoise. P300 was elicited through the Bio-Logic Traveler Express AuditoryEvokedPotentialMachine(ANSI,1996),usingTDH 39earphones.Toevaluate P300,the activeelectrodewas positionedatCz,thereferenceelectrodeswerepositioned onthe right(A2) andleft(A1)mastoids(a linkedmastoid electroderegardlessofearofpresentation),andtheground electrodewaspositionedatFz.24Atoneburstat1500Hzwas
usedasdeviant (rare stimulus),presented randomly with 20%probability,mixedwithafrequenttoneburststimulus at1000Hzandpresentedwith80%probabilityusingthe odd-ballparadigm,70dBHLintensityandarateofonestimulus per second. Individuals were asked to verbally count the rarestimuli.P300wasidentifiedasthepositivedeflection 250---500msafterthestimulus.
Toverifythesuppressioneffect,thetest wasrepeated withtheuse ofwhite noise (WN)in thecontralateral ear withthe sameintensity asthetone burst(70dB HL). The WNwasgeneratedbyBio-LogicSystem.Suppressionvalues for both thelatency and amplitude parameterswere cal-culatedbysubtractingthevalueobtainedwithnoise from the value obtained without noise (latency value without noise−latencyvaluewithnoise).Theresponsesuppression
effectoflatencyisinverselyproportionaltotheamplitude; thus,whilethelatencyvaluesareexpectedtoincreasein thepresence ofcontralateral noise,the amplitudevalues shoulddecrease.
Inthepresentstudy,theexaminerapplyingthetestwas also responsible for the analysis of its results; thus, this was not a blind study. Although it could be argued that suchanalysismaybeinfluencedbyitssubjectiveaspects, the authors donot believe this influence undermines the obtained results. When interference was observed during thesweeping,anewsweepwasperformed.
The intra-and inter-groupanalyses were basedonthe verificationof thenumericalvaluesof thelatency,in ms, andoftheamplitudes,inV,oftheP300intheevaluation
withandwithoutcontralateralnoiseandonthecomparison ofthevaluesobtainedineach situation.Thesedatawere subjected tothe Kolmogorov---Smirnov test, and a normal distributionwasobservedforallofthedatasets.
Table1 ComparisonoftheP300latencyvalues(ms) with-outcontralateral noise between theNMG andMGfor the rightandleftear.
P300latency withoutnoise(ms)
Rightear Leftear
NMG MG NMG MG
Mean 324.48 305.2 313.64 309.13
Median 325 303 324 307.5
SD 35.98 35.63 46.61 41.25
Minimum 257 254 221 232
Maximum 377 372 385 404
Size 25 30 25 30
p-Value 0.035 0.705
NMG,groupofnon-musicians;MG,groupofmusicians.
valuesweremarkedwithanasteriskwhen≤0.05.Statistical analysiswasperformedusingtheSPSSsoftware.
Results
Table1showsdescriptivestatisticsofthedataobtainedin the comparison of the P300 latency valueswithout noise betweentheNMGandMGfortherightandleftear.
ItwasobservedthatthemeanP300latencywithout con-tralateralnoiseintheNMGwasgreaterthanthatobserved in theMG. However,this differencewasonly statistically significantfortherightear[F1.53=4.67;p=0.035].
Using the t-test for dependent samples, no statisti-callysignificantdifferenceswereobserved ineithergroup in the comparison between the left and right ears for theP300latencyvalueswithoutcontralateralnoise[NMG:
t(24)=1.052;p=0.30;MG:t(29)=−0.831;p=0.41]. Table 2 presents descriptive statistics of the data obtainedinthecomparisonbetweentheP300latency val-ueswithcontralateralnoisethatwereobtainedbytheNMG andMGfortherightandleftears.
Nostatisticallysignificantdifferenceswereobservedin thecomparisonoftheP300latencyvalueswithcontralateral noisebetween theNMGandthe MGforthe rightand left ears.
Table 2 Comparison of the P300 latency values (ms) obtainedwithcontralateralnoisebetweentheNMGandthe MGfortherightandleftears.
P300latencywith noise(ms)
Rightear Leftear
NMG MG NMG MG
Mean 320.68 333.00 312.64 330.63
Median 321.00 328.00 312.00 324.50
SD 41.73 35.63 44.27 47.00
Minimum 247.00 272.00 237.00 242.00 Maximum 413.00 408.00 395.00 430.00
Size 25 30 25 30
p-Value 0.243 0.153
NMG,groupofnon-musicians;MG,groupofmusicians.
Table 3 Comparison between the P300 amplitude (V) withoutcontralateral noise betweentheNMGandtheMG fortherightandleftears.
P300amplitude withoutnoise(V)
Rightear Leftear
NMG MG NMG MG
Mean 10.81 19.93 9.55 18.21
Median 9.46 20.85 9.71 18.10
SD 5.13 9.02 3.55 7.45
Minimum 4.11 4.51 3.67 4.59
Maximum 25.21 39.12 15.11 30.4
Size 25 30 25 30
p-Value <0.001 <0.001
NMG,groupofnon-musicians;MG,groupofmusicians.
No statistically significant differences were observed betweentheearsineithergroupfortheP300latency val-ues with contralateralnoise [NMG: t(24)=1.100; p=0.28; MG:t(29)=0.425;p=0.67].
Table3showsdescriptivestatisticsofthedataobtained in the comparison of the P300 amplitude values without competitivenoisebetweentheNMGandtheMGfortheright andleftears.
Statisticallysignificantdifferenceswereobservedwhen comparingtheP300amplitudevaluesbetweentheNMGand MGfor both theright ear[F1.53=20.06;p<0.001] andthe
leftear[F1.53=28.25;p<0.0001].
Nostatisticallysignificant differenceswereobserved in eithergroupinthecomparisonoftheP300amplitude val-ues between the ears without contralateral noise [NMG:
t(24)=1.485;p=0.15;MG:t(29)=1.847;p=0.07].
Table4showsthecomparisonsoftheNMGandMGwith respecttotheresultsfoundfortheP300amplitudevalues withcontralateralnoisefortherightandleftear.
Statistically significant differences were found in the comparison of the P300 amplitude values with contralat-eralnoisebetweentheNMGandtheMGforboththeright ear[F1.53=27.03;p<0.001]andtheleftear[F1.53=19.902;
p<0.001].
In the comparison between the ears for the NMG, no statistically significant differences were observed in the P300amplitudevalueswithcontralateralnoise [NMG;
Table4 ComparisonoftheP300amplitudes(V)with con-tralateralnoisebetweentheNMGandMGfortherightand leftears.
P300amplitude withnoise(V)
Rightear Leftear
NMG MG NMG MG
Mean 9.79 19.62 8.58 16.85
Median 8.04 18.43 6.29 16.48
SD 5.73 7.86 5.60 7.71
Minimum 2.80 7.5 2.81 4.59
Maximum 23.60 39.8 21.22 38.89
Size 25 30 25 30
p-Value <0.001 <0.001
Table5 ComparisonoftheP300latencysuppression(ms) betweentheNMGandtheMGfortherightandleftears.
Latency suppression(ms)
Rightear Leftear
NMG MG NMG MG
Mean 3.80 −27.80 1.00 −21.50
Median 4.00 −24.50 −5.00 −20.50
SD 34.82 29.31 30.67 37.50
Minimum −72.00 −102.00 −73.00 −125.00
Maximum 84.00 21.00 54.00 44.00
Size 25 30 25 30
p-Value <0.001 0.020
NMG,groupofnon-musicians;MG,groupofmusicians.
t(24)=1.300; p=0.290]. For the MG, a statistically sig-nificant differencewas found between the right and left earsfortheP300amplitudevalueswithcontralateralnoise [t(29)=3.357;p=0.002].
Table5showsdescriptivestatisticsfor thecomparisons betweentheNMGandtheMGregardingtheresultsobserved fortheP300latencysuppressionvalues.
Statistically significant differences were found in the comparison of the P300 latency suppressionbetween the NMG and the MG for both the right ear [F1.53=13m35;
p=0.001]andtheleftear[F1.53=5.77;p=0.020].
NostatisticallysignificantdifferencesintheP300latency suppression values were observed in either group in the comparisonbetweenears[NMG:t(24)=0.308;p=0.76;MG:
t(29)=0.950;p=0.35].
Table6presentsdescriptivestatisticsforthecomparisons betweentheNMGandtheMGregardingtheresultsobserved fortheP300amplitudesuppressionvalues.
Nostatisticallysignificantdifferenceswereobservedin the comparisonof the P300 amplitudesuppression values betweentheNMGandtheMGfortherightear[F1.53=0.257;
p=0.615]andtheleftear[F1.53=0.08;p=0.779].
Additionally,nostatisticallysignificantdifferenceswere observed in the comparison between the right and left ears for the P300 amplitude suppression values [NMG:
t(24)=0.05;p=0.95;MG:t(29)=−0.814;p=0.42].
Intheintra-groupcomparison,theP300latencyobtained intheabsenceandpresenceofcontralateralnoisewasnot
Table 6 Comparison of the P300 amplitude suppression (V) between theNMGandthe MGfor the rightandleft ears.
Amplitude suppression(V)
Rightear Leftear
NMG MG NMG MG
Mean 1.02 0.31 0.96 1.35
Median 0.72 0.41 1.92 2.21
SD 4.25 5.82 3.99 5.81
Minimum −11.76 −11.09 −8.94 −12.42
Maximum 9.40 18.04 6.55 12.64
Size 25 30 25 30
p-Value 0.615 0.779
NMG,groupofnon-musicians;MG,groupofmusicians.
significantly affected by the contralateral noise effect in theNMGforeithertherightear[F(1,24)=1.446;p=0.241] or the left ear [F(1,24)=1.476; p=0.236]. However, in theMG,contralateralnoisesignificantlyaffectedtheP300 latency value, causing a significant increase in this mea-sureinboth ears[rightear:F(1,29)=26.97;p<0.001; left ear:F(1,29)=9.861; p=0.004]. However, the P300 ampli-tude valuewas notsignificantly affectedby the effectof contralateralnoiseineithergroup.
Discussion
This study provided evidence that: (1) the MGhad lower averagelatencyvaluesandhigheraverageamplitudes com-pared to NMG in P300 without contralateral noise. This differencewasstatisticallysignificantforamplitudevalues in both ears, but it was significant only in the right ear for latency values; (2) regarding P300 with contralateral noise,theMGalsopresentedsignificantlyhigheramplitude valueswhencomparedwiththeNMG,althoughno statisti-callysignificantdifferencewasobservedbetweenthegroups for latency values; however, (3) no laterality effect was observed(differencebetweentherightandleftears)inany ofthe groups; and (4)the analysisof the noiseeffect on theP300response(intra-groupanalysis)demonstratedthat thelatencyvalueswere significantlyincreasedinthe MG. Nevertheless,thisresponsewasnotobservedin theNMG. Inaddition,fortheamplitudevalues,thepresenceofnoise didnotsignificantlyaffecttheresponseforeithergroup.
Differencesbetweenmusiciansandnon-musicians withoutcontralateralstimulation
The superior performance reportedin the MG, evidenced bylowerlatenciesandhigheramplitudes,corroboratesthe findings of other studies that observed lower latency for AEPsin musicians when compared withnon-musicians.5,11
Althoughpreviousstudieshadverifieddifferencesbetween musiciansandnon-musiciansinbothears,25---27inthepresent
studynostatisticallysignificantdifferencesbetweenlatency valuesinleftearwereobserved.Theauthorsattributethis fact to the small sample and the wide age range of the participants.
TheP300latencycanbeusedasameasureofthespeed ofinformationprocessinginanoddballparadigm.Thus,it issuggestedthatthereducedlatencyobservedinmusicians mayberelatedtothefaster transmissionand categoriza-tionofthestimulus,aswellasthegreatereffectivenessin discriminatingthetargetstimulus,which canbejustified, inthiscase,bythemusicalstimulation.5
RegardingtheP300amplitudevalues,statistically signif-icantdifferenceswereobservedbetweentheNMGandthe MGforbothrightandleftears(Table3).Thisfindingisalso inagreementwiththeliterature,ashigheramplitudevalues inmusiciansreflectmoreneuralconnectionsintheauditory pathwayandsuggestthatmusicaltraininghasaneffect.3---5
amplitudes,28---30astheseindividualsexhibitmoreaccurate
auditoryinformationprocessingandmoreeffective involv-ingauditorypitchdiscrimination.Anotherpossiblecauseof thelowerlatencyvaluesobservedintheMGmaybethe pres-enceof enhancedneural generators in the cortex, whose capacityto evaluate acoustic stimuli is better and faster thaninnon-musicians.Therefore,thestimulationanalysis timeisshorterinthisgroup,resultinginsmallerlatencies.31
The improvement in auditory processing in musically trainedindividualsprobablymodifiesthecortical organiza-tion, and those changes can be extended to sub-cortical sensory structures. Such changes have been observed throughout the auditory pathway, fromthe brain stem to thecortex.5Certainauthorsalsoreportthatthebrainstem
responsesofmusiciansaremorerobust,reflectingalongthe entirepathway.Thisgreaterrobustnesscouldberelatedto neuralresponsesthataremoresynchronizedtotheonsetof sound,whichischaracteristicofahighlyfunctional periph-eralauditorysystem.
How musicians perform ontasks that depend on audi-toryabilities motivates hypothesesconcerningthe impact ofmusic trainingonbrainmechanismsthat underlie audi-toryattentionandworkingmemory.Duringsuchtasks(e.g., when subjects are instructed to listen for certain tar-get tones or timbres), musicians demonstrate heightened recruitmentofcorticalareasassociatedwithsustained audi-toryattentionandworkingmemory,17 suchasthesuperior
parietal cortex, as well as more consistent activation of prefrontal control regions.32 Indications that music
train-ingincreasesthecontributionsofthesuperiorparietaland prefrontalcorticestoactiveauditoryprocessingandtheir rolesinsustainingauditory attentionandworking memory maysupportthe hypothesis that music training tunesthe brain’sauditory cognitivenetworksforcross-domain audi-toryprocessing.
Effectofcontralateralnoiseontheresponsesof musiciansandnon-musicians
This study demonstrated that P300 presented different behaviors in the presence and absence of contralateral noise, especially in musicians. The musician’s average latencyforP300inthepresenceofcontralateralnoisewas significantlylaterthanwithoutthecontralateralnoise.This differenceinP300latencieswithandwithoutcontralateral noisewasnotobservedinNMG.Inaddition,forthe ampli-tudevalues,thepresenceofnoisedidnotsignificantlyaffect theresponseforeithergroup.
Studies of P300with masking noise alsodemonstrated increasedlatencies with unaffectedamplitudes.33,34
How-ever, in a recent study,Schochat etal.22 did not observe
differencesregardingP300latencieswithandwithout con-tralateralnoiseinnormaladults.
No statistically significant difference was observed betweengroupsforP300latencyvalueswithcontralateral noise. Still, it is possible tonote that MG latencies were moreaffectedbycontralateralnoiseincomparisontoNMG, onceMGlatencieswerelaterthanNMGs.
However,fortheP300amplitudevalues,thedifference between groups remained, and the MG presented signifi-cantlyhigheramplitudevaluescomparedwiththeNMG.
In addition, when comparing the suppression values betweenthegroups,themusiciansshowedhigher suppres-sionvalues.
These findings, altogether, may be explained by the inhibitory effect the contralateral noise has on P300 responses, more specifically, on latency measures, which shows more vulnerability to this inhibitory effect. The latencymeasurehasbeenrelatedtotheprocessingof audi-toryinformationandtoauditorydiscrimination,35 andthis
isconsideredthemostreliablemeasureintheP300study. Schochatelal.22observedthepresenceoftheinhibitory
effectusingacontralateralnoiseinbothotoacoustic emis-sion (OAE) and the late auditory potential P300. Studies using TOAE have described this inhibitory effect as the decreaseofthecochlearresponsethroughtheactivationof theMOCinthepresenceofcontralateralnoise.This mech-anism may provide an anti-masking effect that increases the discrimination of signal variation. In addition,it sup-plies afeedback gain-controlsystem for moderate sounds levelsthatmediatesselectiveattentionandfocuses atten-tion during learning.36,37 Although the techniques used in
thepresentstudyaredifferentfromthoseaforementioned, in general,thepresent findingscorroboratethe inhibitory effectactions,mostprobablybyefferentsystemactivation, usingP300.
Thefunction of themedialefferent system iscomplex and stillnot clear, asit involves different mechanisms of action mediated by the medial and lateralolivary tracts. However,evidencepresentedbyseveralstudieshasshown that the MOCB plays an important role in the capacity ofspeechintelligibilityinnoise conditions.Recent studies usingcochlear computermodeling andspeechrecognition haveshownthattheactivationoftheMOCBeffectimproved speechrecognitioninnoiseconditions.38Thus,MOCB
activ-ity in humans should be of great importance for both thefunctioning ofthe peripheralauditory system andthe improvement of auditory signal processing,especially for listening in noise conditions.39 The efferent system also
contributes to the optimization of the discrimination of interaural differences at high frequency signals, increas-ing the differencebetween the information that reaches both cores of the superior olivary complex. This impor-tantroleoftheefferentpathwayhasrepercussionsonthe ability tolocatesounds ofhigh frequency stimuli.Speech signals,especiallyconsonants, arehighfrequency stimuli, and therefore, the integrity of the auditory system as a wholeisrequiredforverbalinformationtobeappropriately processed.40
The authors also attribute the present findings to the actionoftheefferentsystem.TomchikandLu,41inastudyof
animals’auditorysystem,suggestedthat‘‘primaryafferent neuronsadapttonoise,reducingtheirevokedfiringratesin responsetoanadditionalstimulus,whichmayincreasethe latencyofresponses’’.Theyalsosuggestedthatbroadband noisedisruptsthephase-lockingofprimaryafferentstoan addedstimulus.
showgreaterperceptualauditoryadvantagesandenhanced speechprocessing,aswellasadvantagesinfrequency dis-criminationandtemporalprocessing.
Anotherpossibleexplanationfor thepresentfindingsis related tothe corticofugal modulation theory in humans. Studieshavedemonstratedthatelectricalstimulationinthe auditory cortex may resultin amplitude reductionof the OAEvaluesinthecontralateralear.Otherstudieshavealso suggested a top-down control of the corticofugal descen-dingauditorypathwaysinthemedialolivocochlearefferent system.42,43 Otherstudies,whohavefailedtodemonstrate
correlationsbetweenOAEamplitudeandsuppressioneffect, alsoreinforcethe hypothesisthatthereareother aspects influencinginMOC,suchascorticalmodulation.26,27
Even beyond sub-cortical and cortical functional enhancements, musical trainingmayshape auditory func-tion in structures that are as peripheral as the cochlea; musiciansdemonstrateagreaterdegreeofefferentcontrol over outer hair cell activity along the basilar membrane thannon-musicians.15 Suchcomprehensiveperceptual and
neural enhancements may be driven, at least in part, by strengthened cognitive control over basic auditory processing, as engendered by auditory attention32,44 and
workingmemory,17,18 twoauditorycognitiveskillsthatare
enhancedinmusicians.
Thus, it can be stated that musical training may be animportanttoolforauditorytraining,prevention, habili-tation,andreversionofawiderangeofauditoryprocessing deficits.
Regarding the absence of the laterality effect in both groupsandboth evaluatedconditions,theauthorsbelieve that theseresults canbe explainedbythe fact thatboth hemispheres participate in this cognitive processing task. ThissupportstheviewthatP300reflectsanintegrationof functionofvariousareasofthebrain.
Some shortcomings of this study may have influenced the results: absence of a sample size calculation, broad agerange,broad rangeof yearsofformalmusicpractice, the absence of manual dominance as an inclusion crite-rion,andthe long durationof thetest. Nevertheless, the authors believe that thisstudy presents promising results regarding theuse of newtolls toverify themedial olivo-cochlearefferentsystemactivity,aswellasnewinformation onthisactivitythroughaLLAEPinmusicians.Futurestudies shouldtaketheseshortcomingsintoconsideration.
Conclusion
Inthisstudy,evidenceaboutcorticalinhibition effectwas foundusinganERP(P300)inthepresenceandabsenceof contralateralnoiseconditioninbothgroups.Besides, musi-ciansdemonstratedagreaterinhibitioneffectincomparison with non-musicians, evidencing that the central auditory nervoussystemoftheformerpresentscharacteristic pecu-liarities due to the musical practice to which they are constantlyexposed.
Conflicts
of
interest
Theauthorsdeclaretohavenoconflictsofinterest.
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