INTRODUCTIONTOSLEEPRBENBADISUniversityofSouthFloridaCollegeofMedicineT - PDF document

1 INTRODUCTIONTOSLEEPR.BENBADISUniversityo
INTRODUCTIONTOSLEEPR.BENBADISUniversityofSouthFloridaCollegeofMedicine,Tampa,FloridaINTRODUCTIONBasicPrinciplesEEGrecordssynapticpotentialsfrompyramidalcells.Itis Sleep:AComprehensiveHandbook,EditedbyT.Lee-Chiong.2006JohnWiley&Sons,Inc. limitedtospecializedsurgicalepilepsycentersandisbeyondthescopeofthischapter(forreview,see[6,7]).TechnicalAspectsInhumanclinicalEEG,electrodesareplacedaccordingtoastandardsystemknownasthe10-20system(Figure130.2).Itusesfouranatomicallandmarks(nasion,inion,andthetwopreauricularpoints)fromwhichmeasurementsaremadeandelectrodesareplacedat10%or20%ofthedistances.Therearetwotypesofmontages:bipolarandreferential.Inamontage,eachelectrodeislinkedtothenextalongachain(i.e.,AB,BC,CD,DE).Thetypicallongitudinaloranteroposteriorbipolarmontageisoftenreferredtoasadoublebanana.Anothercommonbipolarmontageisthetransverse(fromlefttorightacrossthehead).Inareferential(ormonopolar)montage,eachelec-trodeislinked(compared)toacommonreference.Ahelp-fulanalogyisthatmeasuringvoltageeldswithelectrodesisakintomeasuringmountainpeaks/altitudeswithsur-veyors[8](Figure130.3).Intermsoflocalization,maxi-mumvoltage(altitude)isindicatedbyaphasereversalonbipolarmontages,orbymaximumamplitudeonreferentialmontages(Figure130.3).Contrarytoacommonmiscon-ception,phasereversalsarenotatallindicativeofanabnormality,andinfacthavenothingtodowiththenatureofavoltageeld(i

2 .e.,thedischargeis).Instead,phasereversa
.e.,thedischargeis).Instead,phasereversalsindicatethemaximum(negativityorpositivity) Figure130.1Polarityconvention.Thisisanarbitrarybutcriticalrule.ByconventionoftheampliersusedinclinicalEEG,anupgoingdeectionindicatesthatinput1(grid1orG1)ismorenegative(orlesspositive)thaninput2(grid2orG2).Thusstate-mentslikepositivityisupnegativityisupmakenosenseunlessitisstatedwhetherthepositivityisatgrid1orgrid2. C3CzFigure130.2The1020systemofelectrodeplacement.Thisusesfouranatomicallandmarks(nasion,inion,andthetwopreauri-cularpoints)fromwhichmeasurementsaremadeandelectrodesareplacedat10%or20%ofthedistances.Lettersrefer(grossly)tothelobe(i.e.,Fp,frontopolar;F,frontal;T,temporal;P,parietal;O,occipital).Odd-numberedelectrodesareontheleft,even-num-beredelectrodesontheright,andmidlineelectrodesaredesignated A-BB-CC-DD-E CDBEACBAED Referential A-REFB-REFD-REFE-REF CDBEACBAED Figure130.3Measuringavoltageeldisanalogoustomeasur-ingthealtitudeofamountain.(a)Onabipolarmontage,amaxi-mumpeak(voltage)isindicatedbyaphasereversal.(b)Onareferentialmontage,amaximumpeak(voltage)isindicatedbythehighestamplitude.INTRODUCTIONTOSLEEPELECTROENCEPHALOGRAPHY andhaveeverythingtodowiththelocationofthedischargewherethedischargeis).ThedisplayonEEGtypicallyusesapaperspeed(obsoleteconceptwithdigitalrecordings)of3cm/s(intheUnitedStates),thatis,3timesfasterthanthePSGpaperspeedof1cm/s.Byconvent

3 ion,intheUnitedStates,montagesareusually
ion,intheUnitedStates,montagesareusuallydisplayedleftoverright.Filtersandtheirprinciplesaresimilartothoseusedinpolysomnography.Inclinicalneurophysiologey(e.g.,EEG,PSG),wave-formsanddischargesaredescribedandcharacterizedbythefollowingparameters:Amplitude:howhighthevoltageis(inV).Duration:howlongthedischargeis(inmsorseconds).Frequency:howfrequentlyawaveformrepeatsitself(incyclespersecondsorhertz).Thefrequencyisthereciprocaloftheduration(e.g.,adurationon200msisthesameasafrequency5Hz.)Morphology:theshapeandcongurationofthedis-charge(thisisqualitative).Latency:thedelaybetweenanarbitraryevent(e.g.,stimulus)andanotherevent(inms).Location:wherethedischargeis.Reactivity:whataffectsthedischarge.ARTIFACTSAlthoughEEGisdesignedtorecordcerebralactivity,italsorecordselectricalactivitiesarisingfromsitesotherthanthebrain.Therecordedactivitythatisnotofcerebraloriginistermedartifactandcanbeconvenientlydividedintophysiologicandextraphysiologicartifacts.Physiologicartifactsaregeneratedbythebodybutarisefromsourcesotherthanthebrain.artifactsarisefromoutsidethebody(i.e.,equipment,environment).PhysiologicArtifactsMuscle(Electromyogram)ActivityMyogenicpotentialsareprobablythemostcommonartifactsandareseenonvirtuallyallEEGperformedinclinicalpractice.Frontalisandtemporalismuscles(e.g.,clenchingofjawmuscles)areparticularlycommon.Asageneralrule,thepotentialsgeneratedinthemuscl

4 esareofshorterdurationthanthosegenerated
esareofshorterdurationthanthosegeneratedinthebrainandareidentiedeasilyonthebasisofduration,morphology,andhighfrequencyof100Hz(Figures130.4and130.10].Aparticulartypeofmuscleartifactischewing,characterizedbyrhyth-micburstsofmusclemaximuminthetemporalchains(Figure130.5). Figure130.4Muscle(EMG)andEKGartifact.Muscleartifactisseenashigh-amplitude,veryfast(50Hz),andvariablefrequencydis-charges,whicharemoreprominentontheleftinthissample.EKGiseasilyidentiedinseveralchannelsasclearlysimultaneoustotheEKGARTIFACTS GlossokineticArtifactInadditiontomuscleactivity,thetongue(liketheeyeball)functionsasadipole,withthetipnegativewithrespecttothebase.Inthiscasethetipofthetongueisthemostimportantpartbecauseitismoremobile.Theartifactproducedbythetonguehasabroadpotentialeldthatdropsfromfrontaltooccipitalareas,althoughitislesssteepthanthatproducedbyeyemovementartifacts.Theamplitudeofthepotentialsisgreaterinferiorlythaninparasagittalregions;thefrequencyisvariablebutusuallyinthedeltarangeandoccurssynchronouslywhenthepatientLah-lah-lah-lah,whichcanbeveriedbythetech-nologist.Chewingandsucking(pacier)canproducesimi-larartifacts.EKGArtifactSomeindividualvariationsintheamountandpersistenceofEKGartifactarerelatedtotheeldoftheheartpotentialsoverthesurfaceofthescalp.Generally,subjectswithshortandwideneckshavethelargestEKGartifactsontheirEEGrecordings.Thevoltageandapparentsurfaceo

5 ftheartifactvaryfromderivationtoderivati
ftheartifactvaryfromderivationtoderivationand,consequently,frommontagetomontage.Theartifactisobservedbestinreferentialmontagesusingearelectrodes(A1andA2).EKGartifactisrecognizedeasilybyitsrhythmicityandcoincidencewiththeEKGtracing(Figure130.4).Thesituationbecomesdifcultwhenabnor-malcerebralactivity(e.g.,sharporslowwaves)appearsintermixedwithEEGartifact.PulseartifactoccurswhenanEEGelectrodeisplacedoverapulsatingvessel.ThepulsationcancauseslowwavesthatmaysimulateEEGactivity.Adirectrela-tionshipexistsbetweenEKGandthepulsewaves.TheQRS Figure130.5Chewingartifact.ThisEMGartifactoccursinrhythmicburstsofmusclemaximuminthetemporalchains.INTRODUCTIONTOSLEEPELECTROENCEPHALOGRAPHY complex(i.e.,electricalcomponentoftheheartcontraction)happensslightlyaheadofthepulsewaves200300msecdelayafterEKG.EyeMovementsEyemovementsareobservedonallEEGrecordingsandareusefulinidentifyingsleepstages.Theeyeballactsasadipolewithapositivepoleanteriorly(cor-nea)andanegativepoleposteriorly(retina).Whenthegloberotatesaboutitsaxis,itgeneratesalarge-amplitudealternatecurrenteld,whichisdetectablebyanyelectrodesneartheeye.TheothersourceofartifactscomesfromEMGpotentialsfrommusclesinandaroundtheorbit.Verticaleyemovementstypicallyareobservedwithblinks(i.e.,sphenomenon).Ablinkcausesthepositivepole(i.e.,cornea)tomoveclosertofrontopolar(Fp1Fp2)electrodes,producingsymmetricdownwarddeections.Dur

6 ingdownwardeyemovementthepositivepole(i.
ingdownwardeyemovementthepositivepole(i.e.,cornea)oftheglobemovesawayfromfrontopolarelectro-des,producinganupwarddeectionbestrecordedinchan-nels1and5inthebipolarlongitudinalmontage.LateraleyemovementsaffectlateralfrontalelectrodesF7andF8(whicharejustaboutwhereeyeelectrodesofthePSGwouldbe).Duringaleftlateraleyemovement,thepositivepoleoftheglobemovestowardF7andawayfromF8.Usingabipolarlongitudinalmontage,thereisamaximumpositivityinelectrodeF7andmaximumnegativitysimultaneouslyinelectrodeF8(Figure130.6).Aso-calledlateralrectusspike(Figure130.7)maybepresentinelec-trodeF7.Withrightlateraleyemovement,theopposite Figure130.6EyemovementsandsawtoothwavesinREMsleep.Duringthisrapidlateraleyemovementtotheleft,thereisamaximumpositivityinelectrodeF7andmaximumnegativitysimultaneouslyinelectrodeF8.Inthevicinityoftherapideyemovement,therearetypicalsawtoothwavesinthecentralregion(C3andC4).ARTIFACTS RespirationArtifactsRespirationcanproducetwokindsofartifacts.Onetypeisintheformofslowandrhythmicactivity,synchronouswiththebodymovementsofrespira-tionandmechanicallyaffectingtheimpedanceof(usually)oneelectrode.Theothertypecanbesloworsharpwavesthatoccursynchronouslywithinhalationorexhalationandinvolvethoseelectrodesonwhichthepatientislying.SeveralcommerciallyavailabledevicestomonitorrespirationcanbecoupledtotheEEGmachine.AswiththeEKG,onechannelcanbededicatedtorespiratorymo

7 vements.SkinArtifactsBiologicalprocesses
vements.SkinArtifactsBiologicalprocessesmayalterimpedanceandcauseartifacts.Sweatisacommoncause(Fig-ure130.8).Sodiumchlorideandlacticacidfromsweatingreactwithmetalsoftheelectrodesandproducelargeandveryslow(usually0.5Hz)baselinesways.ExtraphysiologicArtifactsElectrodeArtifactsThemostcommonelectrodeartifactistheelectrodeMorphologicallythisappearsassin-gleormultiplesharpwaveformsduetoabruptimpedancechange.Itisidentiedeasilybyitscharacteristicappear-ance(i.e.,abruptverticaltransientthatdoesnotmodifythebackgroundactivity)anditsusualdistribution,whichislimitedtoasingleelectrode(Figure130.9).Ingeneral,sharptransientsthatoccuratasingleelectrode(i.e.,eld)shouldbeconsideredartifactsuntilprovedother-wise.Atothertimes,theimpedancechangeislessabrupt, Figure130.7Rapideyemovementsandlateralrectusspikes.Withtheeyemovementstotheleft,lateralrectusspikesareseeninelectrodeF7.INTRODUCTIONTOSLEEPELECTROENCEPHALOGRAPHY Figure130.8Sweatartifact.Notetheveryslow(0.5Hz)sways.Theslowfrequencyissimilartoslowrollingeyemovements,butthedistributionisnot(inthiscaseitaffectselectrodesontheleftsideofthehead). Figure130.9Electrodeartifact.ThistypicalelectrodeartifactistheelectrodeNotethesinglesharpwaveformwithabruptverticaltransientthatdoesnotmodifythebackgroundactivity,anditsdistribution,whichislimitedtoasingleelectrode(P4).ARTIFACTS andtheartifactmaymimicalow-voltagearrhythmicdelt

8 awave.AlternatingCurrent(60Hz)ArtifactAd
awave.AlternatingCurrent(60Hz)ArtifactAdequateground-ingonthepatienthasalmosteliminatedthistypeofartifactfrompowerlines.Theproblemariseswhentheimpedanceofoneoftheactiveelectrodesbecomessignicantlylargebetweentheelectrodesandthegroundoftheamplier.Inthissituation,thegroundbecomesanactiveelectrodethat,dependingonitslocation,producesthe60Hzartifact.Theartifacthastheexactfrequencyof60Hzandiseasilyidentiedbyincreasingthetimebase(Figure130.10).MovementsintheEnvironmentMovementofotherper-sonsaroundthepatientcangenerateartifacts,usuallyofcapacitiveorelectrostaticorigin.Theartifactproducedbyrespiratorsvarieswidelyinmorphologyandfrequency.Monitoringtheventilatorrateinaseparatechannelhelpstoidentifythistypeofartifact.Interferencefromhigh-frequencyradiationfromradio,TV,hospitalpagingsystems,andotherelectronicdevicescanoverloadEEGers.Thecuttingorcoagulatingelectrodeusedintheoperatingroomalsogenerateshigh-voltagehigh-fre-quencysignalsthatinterferewiththerecordingsystem.Touchingorhittingelectrodescanproduceoddwaveforms, Figure130.10The60Hzandmuscle(EMG)artifact.The60HzartifactisatelectrodeO2(thusseeninchannelsT6O2andP4O2).Notethatitsamplitudeisperfectlyregularandexactlyandsteadilyat60Hz.EMG(muscle)artifact,bycontrast,isofcomparablefrequencybutaffectsseveralelectrodes,isvariableinamplitude,andvariableinfrequency(notalwaysnorexactlyat60Hz).INTRODUCTIONTOSLEEPELECT

9 ROENCEPHALOGRAPHY and,forexample,repetit
ROENCEPHALOGRAPHY and,forexample,repetitiveheadmovementscanproducerhythmicartifacts(Figure130.11).PhoticStimulationPhoticstimulationisperformedduringroutineEEGrecord-ingsandcanproducesomephysiologicandsomeextraphy-siologicartifacts,soitisdescribedhereseparately.Photicdrivingisanormalphysiologicresponse,whichisactuallyavisualevokedpotential.Itistheoccipitalcor-texresponsetoashinglightsandisthusseenintheocci-pitalregion(electrodesO1andO2).Itiseasilyidentibecauseitistime-lockedwith(samefrequencyas)thestrobelight(Figure130.12).photomyoclonicresponseisaspecialtypeofEMGartifactthatoccursduringintermittentphoticstimulation.Somesubjectscontractthefrontalisandorbicularismuscles.Thissuperciallyresemblesnormalphoticdrivingbutisfrontal(Figure130.13),whereasnormalphoticdriv-ingisoccipital.Ascanbeshownbyspreadingthetimebase,thesecontractionsoccurapproximately5060maftereachphotocell(photoelectric)artifactcanalsobeseenwithphoticstimulation.Thisaffectsoneelectrode(Figure130.14)andiseasilyidentiedasitdisappearsifoneblocksthelightfromtheelectrodeinquestion.THENORMALEEGCommonPatternsofWakefulnessAlphaRhythmThealpharhythm(Figure130.15)istypicallywhatEEGreadersidentifyrst.Thenormalalpharhythmhasthefollowingcharacteristics:Frequencyof812Hz:Lowerlimitofnormalgener-allyacceptedinadultsandchildrenolderthan8yearsis8Hz.Location:Posteriordominant;occasionally,themaxi-mummayb

10 ealittlemoreanterior,anditmaybemorewides
ealittlemoreanterior,anditmaybemorewidespread.Morphology:Rhythmic,regular,andwaxingand Figure130.11Movementartifact.Thisisanexampleofrhythmicartifactgeneratedbyrepetitivemovements(shakingtheheadonthepillowhittingtherightposteriorelectrodesT6andO2).Thisshouldnotbemistakenforafocalseizure.NotethephasereversalT6,eventhoughthisisanartifact.THENORMALEEG Figure130.12Normalphoticdriving.Bioccipitalrhythmicactivitytime-lockedwith(samefrequencyas)thestrobelight(thefrequencyisshownaslinesatthebottom).Usually,photicdrivingisseenatseveralfrequencies,suchasshownhere.Notethatonlylocationdifferentiatesthisfrom(frontal)photomyoclonic(orphotomyogenic)response(Figure130.13). Figure130.13Photomyoclonic(orphotomyogenic)response.Bifrontalrhythmicactivitytime-lockedwith(samefrequencyas)thestrobelight(theashfrequencyisshownaslinesatthebottom).Notethatonlylocationdifferentiatesthisfrom(occipital)photicdriving(Figure130.12).INTRODUCTIONTOSLEEPELECTROENCEPHALOGRAPHY Amplitude:Generally20Reactivity:Bestseenwitheyesclosed;attenuateswitheyeopening.Occasionallythealpharhythmisofverylowamplitudeorevennotidentiable.Thisisnotinitselfabnormal.Inadditiontoamplitude,othercharacteristicscanvarysome-whatwithoutbeingabnormal,includingmorphology(e.g.,spiky),distribution(e.g.,widespread),andharmonicfrequency(e.g.,sloworfastalphavariant).BetaActivityNormalbetaactivity(Figure130.16)hasthe

11 followingcharacteristics:Frequency(byden
followingcharacteristics:Frequency(bydenition)greaterthan13Hz,typically25Hz.Location:Mostlyfrontocentralbutsomewhatvari-able;somedescribevarioustypesaccordingtolocationandreactivitygeneralized,precentral,andposterior.Morphology:Usuallyrhythmic,waxingandwaning,andsymmetric.Amplitude:Usuallyintherangeof5Reactivity:Mostcommon1825Hzbetaactivityenhancedduringstages1and2sleepandtendstodecreaseduringdeepersleepstages;centralbetaactiv-itymaybereactive(attenuates)tovoluntarymove-mentsandproprioceptivestimuli;ininfantsolderthan6months,onsetofsleepmarkedbyincreasedbetaactivityincentralandpostcentralregions.Inhealthyindividuals,betaactivitycommonlycanbemildlydifferent(35%)inamplitudebetweenthetwohemispheres,whichmaybecausedbydifferencesinskullthickness.Theamountandvoltageofbetaactivityisenhancedbycommonlyusedsedativemedications(benzo-diazepines,barbiturates). Figure130.14Photocell(photoelectric)artifact.Thisisproducedatonesingleelectrode(usuallyfrontalratherthanoccipital)andisedbybeingtime-lockedwiththestrobe.Itwouldalsodisappearifoneshieldedtheelectrodeinquestionfromthelight.THENORMALEEG MuRhythmCharacteristicsofthemurhythm(Fig-ure130.17)areasfollows:Frequencyof711Hz:Generallyinalphafrequencyband(812Hz).Location:Centroparietalarea.Morphology:Arch-likeshapeorlikean;mostoftenasymmetricandasynchronousbetweenthetwosidesandmaybeunilateral.Amplitude:Generallylowt

12 omediumandcomparabletothatofthealpharhyt
omediumandcomparabletothatofthealpharhythm.Reactivity:murhythmattenuateswithcontralateralextremitymovement,thethoughtofamovement,ortactilestimulation.Asymmetry,unilaterality,orasynchronyofthemurhythmisnotabnormalunlessassociatedwithotherabnormalities.Veryhighvoltagemuactivitymayberecordedinthecentralregionsoverskulldefectsandmaybecomesharpincongurationandthuscanbemistakenforepileptiformdischarges.WhenmurhythmisdetectedinanEEG,itshouldbeveriedbytestingitsreactivity.CommonPatternsofSleepSleepArchitectureSleepgenerallyisdividedintwobroadtypes:non-rapideyemovement(NREM)andrapideyemovement(REM)sleep.OnthebasisofEEGchanges,NREMsleepisdividedfurtherintofourstages(stage1,stage2,stage3,stage4).REMsleepisdenednotonly Figure130.15Normalalpharhythm.Thissampledepictsthetypicalwell-formedsinusoidalrhythmicactivityat9HzintheoccipitalINTRODUCTIONTOSLEEPELECTROENCEPHALOGRAPHY Figure130.16Normalbetaactivity.Thissampledepictsthetypicalfast(25Hz)low-amplitudeactivityinbothfrontalregions.Asshownhere,normalamountsofbetaactivityaremoderateandtendtowaxandwane. Figure130.17Murhythm.Thissampledepictsthetypicalm-shapedbicentralburstsatafrequencyof812Hz.Iftested,thiswouldreact(attenuate)tocontralateralmovement.THENORMALEEG byEEG,butalsobyEMGandeyemovements.NREMandREMsleepoccurinalternatingcycles,eachlastingapproximately90100minutes,withatotalof46cycles.Ingeneral,inthehealth

13 yyoungadultNREMsleepaccountsfor7590%ofsl
yyoungadultNREMsleepaccountsfor7590%ofsleeptime(35%stage1,60%stage2,and1020%stages3and4).REMsleepaccountsfor1025%ofsleeptime.Totalsleeptimeinthehealthyyoungadultapproximates10hours.Inthefull-termnewborn,sleepcycleslastapproximately60minutes.Thenewbornsleepsapproxi-mately1620hoursperday,withahigherproportion50%)ofREMsleep.Stage1(‘‘Drowsiness’’)Slowrollingeyemovements(SREMs)(Figure130.18)areusuallytherstevidenceofdrowsinessseenontheEEG.SREMsofdrowsinessmostoftenarehorizontalbutcanbeverticaloroblique,andtheirdistributionissimilartoeyemovementsingeneral.However,theyareslow(i.e.,typically0.250.5Hz).Becauseoftheirfrequency,SREMssuperciallyresemblesweatartifactsbutareeasilyidentiedbytheirnonrandomdistributiontypicalofeyemovements(e.g.,phasereversalsatF7andF8ifhorizontal).SREMsdisappearinstage2anddeepersleepstages.Alphaactivitydropout(Figure130.18)typicallyoccurstogetherwithornearbySREMs.Thealpharhythmgradu-allybecomesslower,lessprominent,fragmented,anddisappears.Vertexsharptransients(Figures130.19and130.20),alsocalledvertexwavesorVwaves,arealmostuniversal.AlthoughtheyoftenaregroupedtogetherwithK-com-plexes,strictlyspeaking,vertexsharptransientsaredistinctfromK-complexesbecausetheyarebrieferinduration,smallerinamplitude,andmorefocal(i.e.,lesswidespread).LikeK-complexes,vertexwavesaremaximumatthevertex(centralmidlineplacementofelectrodes(Cz)),sothat,depen

14 dingonthemontage,theymaybeseenonbothside
dingonthemontage,theymaybeseenonbothsides,usuallysymmetrically,atC3andC4.Theiramplitudeis50V.Theycanbecontouredsharplyandoccurinrepetitiveruns,especiallyinchildren.Theypersistinstage2sleepbutusuallydisappearinsubsequentstages.UnlikeK-complexes,vertexwavesdonotdenestage2. Figure130.18Drowsiness(stage1sleep):slowrollingeyemovements.Notetheveryslow(0.30.5Hz)oscillationsatF7andF8.Likerapideyemovements,anegativityatF7occursatthesametimeasapositivityatF8foraneyemovementtotheright,andviceversaforaneyemovementtotheleft.Alsonotetheattenuationandslowingofthealpharhythm(alphadropout)betweentherstandsecondhalfofthesample.Thisistheotherearlyndingofstage1sleep.INTRODUCTIONTOSLEEPELECTROENCEPHALOGRAPHY Positiveoccipitalsharptransientsofsleep(POSTS)(Figure130.19)areseenverycommonlyonEEGandhavebeensaidtobemorecommonduringdaytimenapsthanduringnocturnalsleep.MostcharacteristicsofPOSTSarecontainedintheirname.Theyhaveapositivemaximumattheocciput,arecontouredsharply,andoccurinearlysleep(stages1and2).Theirmorphologyisbestdescribedasreversedcheckmark,andtheiramplitudeis50V.Theytypicallyoccurinrunsof45Hzandarebisynchronous,althoughtheymaybeasymmetric.Theypersistinstage2sleepbutusuallydisappearinsub-sequentstages.Hypnagogichypersynchrony(Figure130.21)isalesscommonbutwellrecognizednormalvariantofdrowsinessinchildrenaged3monthsto13years.Thisisdescribedasparoxysmalbursts(35H

15 z)ofhigh-voltage(ashighasV)rhythmicwaves
z)ofhigh-voltage(ashighasV)rhythmicwaves,maximallyexpressedintheprefrontal-centralareas.Stage2Sleepspindles(Figure130.22)normallyappearininfantsaged68weeksandareinitiallyasynchro-nous,becomingsynchronousbytheageof2years.Sleepspindleshaveafrequencyof1216Hz(typically14Hz)andaremaximalinthecentralregion(vertex),althoughtheyoccasionallypredominateinthefrontalregions.Theyoccurinshortburstsofwaxingandwaningfusiformrhythmicactivity.Amplitudeisusually20V.Lesstypicalorextremespindles(describedbyGibbsandGibbs)areunusuallyhigh-voltage(100400V)andpro-longed(20s)spindleslocatedoverthefrontalregions.K-complexes(Figure130.23)arehighamplitude(V),broad(200ms),diphasic,transientsoftenassociated Figure130.19VertexsharptransientandPOSTS.Thevertexwavesshowthecharacteristicmaximum(phasereversal)atCz.Inthisexam-ple,theyarevery(restrictedtoCz)andarenotseenatC3orC4.POSTS(positivesharptransientsofsleep)areseenwiththeirtypicalbioccipitallocationandreversedcheckmarkmorphology.THENORMALEEG withsleepspindles.Locationisfrontocentral,withatypicalmaximumatthemidline(centralmidlineelectrodes(Cz)orfrontalmidlineelectrodes(Fz)).Theyoccurspontaneouslyorasanarousalresponse.Stage3/4Slow-wavesleep(SWS),ordeltasleep,ischaracterized,asthenameimplies,bydeltaactivity.Thistypicallyisgeneralizedandpolymorphicorsemirhythmic(Figure130.24).Bystrictsleepstagingcriteriaonpolysom-nography,SWSisden

16 edbythepresenceofsuchdeltaactivityformor
edbythepresenceofsuchdeltaactivityformorethan20%ofthetime,andanamplitudecriterionofatleast75Voftenisapplied.Thedistinctionbetweenstages3and4isonlyaquanti-tativeonethathastodowiththeamountofdeltaactivity.Stage3isdenedbydeltaactivitythatoccupies2050%ofthetime,whereasinstage4deltaactivityrepresentsgreaterthan50%ofthetime.SleepspindlesandK-complexesmaypersistinstage3andeventosomedegreeinstage4,buttheyarenotprominent.Asmentionedearlier,SWSusuallyisnotseenduringroutineEEG,whichistoobriefarecording.However,itisseenduringprolongedEEGmonitoring.OneimportantclinicalaspectofSWSisthatcertainparasomniasoccurspecicallyoutofthisstageandmustbedifferentiatedfromseizures.Theseslow-wavesleepparasomniasincludeconfusionalarousals,nightterrors(pavornocturnus),andsleepwalking(somnambulism).REMSleepREMsleepnormallyisnotseenonroutineEEGrecordings,becausethenormallatencytoREMsleep(100min)iswellbeyondthedurationofroutineEEGrecordings(approximately2030min).Theappear-anceofREMsleepduringaroutineEEGisreferredtoassleep-onsetREMperiod(SOREMP)andisabnormalandwarrantsanMSLT.WhilenotobservedonroutineEEG,REMsleepcommonlyisseenduringprolonged(24h)EEGmonitoring. Figure130.20Stage1sleep:vertexsharptransients.Onthistransversebipolarmontage,thevertexwavesshowthecharacteristicmax-imum(phasereversal)atCz.NotethattheyarealsoseenfrontallywithaphasereversalafFz.INTRODUCTIONTOSLEEPELECTROENCE