Neural systems operate in various dynamic states that determine

1999). To investigate the function of a brain area, it is therefore crucial to determine the state of that system. One grave difficulty is that even under well controlled conditions, the thalamocortical network may undergo random dynamic state fluctuations

TheJournalofNeuroscience,September15,2000,20(18):7011–7016

Stimulus-BasedStateControlintheThalamocorticalSystem

LeeM.MillerandChristophE.Schreiner

W.M.KeckCenterforIntegrativeNeuroscience,andUniversityofCaliforniaSanFrancisco/BerkeleyBioengineeringGroup,UniversityofCaliforniaMedicalCenter,SanFrancisco,California94143

Neuralsystemsoperateinvariousdynamicstatesthatdeterminehowtheyprocessinformation(LivingstoneandHubel,1981;FunkeandEysel,1992;MorrowandCasey,1992;Abelesetal.,1995;Guidoetal.,1995;MukherjeeandKaplan,1995;KenmochiandEggermont,1997;Wo¨rgo¨tteretal.,1998;KisleyandGer-stein,1999).Toinvestigatethefunctionofabrainarea,itisthereforecrucialtodeterminethestateofthatsystem.Onegravedif cultyisthatevenunderwellcontrolledconditions,thethalamocorticalnetworkmayundergorandomdynamicstate uctuationswhichalterthemostbasicspatialandtemporalre-sponsepropertiesoftheneurons.Theseuncontrolledstatechangeshindertheevaluationofstate-speci cpropertiesofneuralprocessingand,consequently,theinterpretationofthalamocorticalfunction.

Simultaneousextracellularrecordingsweremadeintheaudi-torythalamusandcortexoftheketamine-anesthetizedcatunderAcommondynamicstateischaracterizedbywidespread,synchro-nousneuralactivityinthethalamusandcerebralcortex.Inpartic-ular,activitywaxesandwanesacrossbothstructuresatarateof7–14Hz.Thisstateoccursinsensory,motor,andassociationsystemsofmanymammals,includinghumans,duringvariousstimulus-drivenandspontaneousepochs,andunderdiversebehavioralconditions(MoruzziandMagoun,1949;Chang,1950;AndersenandAndersson,1968;SteriadeandLlina´s,1988;Buzsa´ki,1991;Tiihonenetal.,1991;Eggermont,1992;MorrowandCasey,1992;Pfurtscheller,1992;Steriadeetal.,1993;ContrerasandSteriade,1996;Llina´setal.,1999;Cotillonetal.,2000).Theoscillatoryactivityisimposedontheneuronalnetworkbytheinhibitorythalamicreticularandexcitatorythalamocorticalcells,whichcan reintwodistinctmodes(SteriadeandLlina´s,1988).Therhythmicor“burst”modetypi esdrowsyorsleepinganimals;thesingle-spikeor“tonic”modeismorecommonlyseeninalertanimals.Inbothawakeandunconsciousanimals,however,random uctuationsbetweenthesemodesoccur(LivingstoneandHubel,1981;MorrowandCasey,1992;MukherjeeandKaplan,1995;GuidoandWeyand,1995).The uctuationsare,moreover,accom-paniedbychangesintheresponsepatternsandinthespatialandtemporalreceptive eldpropertiesoftheneurons(LivingstoneandHubel,1981;FunkeandEysel,1992;MorrowandCasey,1992;Guidoetal.,1995;MukherjeeandKaplan,1995;KenmochiandEggermont,1997;Wo¨rgo¨tteretal.,1998).Uncontrolled,thesechangescanseverelyhindertheevaluationofkeyaspectsofneuralprocessing.

Theideaofintentionallyalteringorarrestingsuchmodes,i.e.,

ReceivedMay1,2000;revisedJune29,2000;acceptedJuly5,2000.

ThisworkwassupportedbytheNationalInstitutesofHealth(DC02260,NS34835),theNationalScienceFoundation(NSF97203398),andtheWhitakerFoundation.WethankMontyA.Escab ´fortheuseofhisdynamicripplestimulusandbothEscab ´andHeatherL.Readformuchhelpintheconceptionandexecutionoftheexperiments.MarkKvaledevelopedthespike-sortingsoftware.JefferyWinerprovidedhelpfulcommentsonthismanuscript.

CorrespondenceshouldbeaddressedtoLeeM.Miller,BuildingHSE-834,P.O.Box0732,513ParnassusAvenue,UniversityofCaliforniaMedicalCenter,SanFrancisco,CA94143.E-mail:lmiller@phy.ucsf.edu.

Copyright©2000SocietyforNeuroscience0270-6474/00/207011-06$15.00/0

severalstimulusconditions.Byconsideringthecellularandnet-workmechanismsthatgovernstatechanges,wedevelopacomplexstimulusthatcontrolsthedynamicstateofthethalamo-corticalnetwork.Traditionalauditorystimulihaveambivalenteffectsonthalamocorticalstate,sometimeselicitinganoscilla-torystateprevalentinsleepinganimalsandothertimessup-pressingit.Bycontrast,ourcomplexstimulusclampsthenet-workinadynamicstateresemblingthatobservedinthealertanimal.Itthusallowsevaluationofneuralinformationprocessingnotconfoundedbyuncontrolledvariations.Stimulus-basedstatecontrolillustratesageneralanddirectmechanismwherebythefunctionalmodesofthebrainarein uencedbystructuralfea-turesoftheexternalworld.

Keywords:dynamicstate;thalamocortical;spindles;oscilla-tions;ketamine;alertingstimuli;burstmode;tonicmodedynamicstatecontrol,hasalonghistoryincentralneurophysiol-ogy.The ringmodeofthalamiccells,andthereforethethalamo-corticalstate,isresponsivetoelectrical,chemical,andsurgicalmanipulation(MoruzziandMagoun,1949;Steriadeetal.,1985;SteriadeandLlina´s,1988;McCormickandvonKrosigk,1992).Whereasthesetraditionalmanipulationsalterthalamicnetworkproperties,theyarenonspeci candmayhavewidespreadandsometimesdevastatingeffectsonthebrain.Previousstudiessug-gest,however,thatsuchextrememethodsarenotessentialtomodulatethalamocorticalstate,andanexternalstimuluswiththeappropriatequalitiesmightsuf ce(MoruzziandMagoun,1949;PompeianoandSwett,1962;Tiihonenetal.,1991).Astimuluswiththesequalitieswouldbede ned,withreferencetothebehavioralcorrelatesofaburst-to-tonicmodechange,an“alertingstimulus”(Tennigkeitetal.,1996).

Clearly,notallstimuliaresuf cienttopreventtheoscillatorymode,because7–14Hzrhythmscanbeelicitedorentrainedbytraditionalclicksandtones,light ashes,mechanicalpinches,andsynchronouselectricalstimulation(Chang,1950;PompeianoandSwett,1962;AndersenandAndersson,1968;Eggermont,1992;Pfurtscheller,1992;ContrerasandSteriade,1996;Dinseetal.,1997).Wedevelopacandidatealertingstimulusfortheauditorymodality,the“dynamicripple”,whosespectrotemporalpropertiesaremotivatedbythecellularandnetworkmechanismsthatregu-latethalamocorticalstatechanges.Wethendeterminewhetherthedynamicripplestimulusaffectstheoscillatorydynamicstateandhowitseffectsdifferfromtraditionalstimuli.

MATERIALSANDMETHODS

Thedynamicripplestimulus(Escab ´etal.,1998)isanelaborationofthestaticandthemovingripplesounds(SchreinerandCalhoun,1994;Ko-walskietal.,1996).Itisatemporallyvaryingbroadbandsoundcomposedof230sinusoidalcarriers(500–20,000Hz)withrandomizedphase.Themagnitudeofanycarrieratanytimeismodulatedbythespectrotemporalenvelope,consistingofsinusoidalamplitudepeaks(“ripples”)onaloga-rithmicfrequencyaxisthatchangethroughtime.Twoparametersde netheenvelope:thenumberofpeaksperoctave,orrippledensity,andthespeedanddirectiontheyaresweeping,ortemporalfrequencymodulation(FM).BothrippledensityandtemporalFMratewerevariedrandomlyandindependentlyduringthe20min,nonrepeatingstimulus.Rippledensityvariedslowly(maximumrateofchange,1Hz)between0and4cyclesper

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