Polyvagal Theory: A Science Of Safety. Frontiers In Integrative

doi:10.3389/fnint.2022.871227

Editedby: DarrenJ.Edwards, SwanseaUniversity,UnitedKingdom

Reviewedby: SaraScrimin, UniversityofPadua,Italy

SoniaPellissier, UniversitéSavoieMontBlanc,France

*Correspondence: StephenW.Porges sporges@indiana.edu; sporges@gmail.com

Received: 07February2022

Accepted: 03March2022

Published: 10May2022

Citation: PorgesSW(2022)Polyvagal Theory:AScienceofSafety. Front.Integr.Neurosci.16:871227. doi: 10.3389/fnint.2022.871227

PolyvagalTheory:AScienceof Safety

StephenW.Porges1,2*

1 TraumaticStressResearchConsortium,KinseyInstitute,IndianaUniversity,Bloomington,IN,UnitedStates, 2 Department ofPsychiatry,UniversityofNorthCarolinaatChapelHill,ChapelHill,NC,UnitedStates

Contemporarystrategiesforhealthandwellbeingfailourbiologicalneedsbynot acknowledgingthatfeelingsofsafetyemergefrominternalphysiologicalstatesregulated bytheautonomicnervoussystem.Thestudyoffeelingsofsafetyhasbeenanelusive constructthathashistoricallybeendependentuponsubjectivity.Acknowledgingthat feelingsofsafetyhaveameasurableunderlyingneurophysiologicalsubstratewouldshift investigationsoffeelingsofsafetyfromasubjectivetoanobjectivescience.Polyvagal Theoryprovidesaninnovativescientificperspectivetostudyfeelingsofsafetythat incorporatesanunderstandingofneuroanatomyandneurophysiology.Thisperspective identifiesneuralcircuitsthatdownregulateneuralregulationofthreatreactionsand functionallyneutralizedefensivestrategiesvianeuralcircuitscommunicatingcues ofsafetythatenablefeelingsofsafetytosupportinterpersonalaccessibilityand homeostaticfunctions.Basically,whenhumansfeelsafe,theirnervoussystemssupport thehomeostaticfunctionsofhealth,growth,andrestoration,whiletheysimultaneously becomeaccessibletootherswithoutfeelingorexpressingthreatandvulnerability. Feelingsofsafetyreflectacorefundamentalprocessthathasenabledhumansto survivethroughtheopportunisticfeaturesoftrustingsocialengagementsthathavecoregulatorycapacitiestomitigatemetabolicallycostlydefensereactions.Throughthe studyofneuraldevelopmentandphylogeny,wecanextractfoundationalprinciples andtheirunderlyingmechanismsthroughwhichtheautonomicnervoussystemleads tofeelingsofsafetyandopportunitiestoco-regulate.Severalprincipleshighlightthe validityofascienceofsafetythatwhenimplementedinsocietalinstitutions,ranging fromhealthcaretoeducation,wouldenhancehealth,sociality,andleadtogreater productivity,creativity,andasenseofwellbeing.Byrespectingourneedtofeelsafe asabiologicalimperativelinkedtosurvival,werespectourphylogeneticheritageand elevatesocialityasaneuromodulatorthatfunctionallyprovidesthescientificvalidation forasocietalfocusonpromotingopportunitiestoexperiencefeelingsofsafetyand co-regulation.

Keywords:polyvagaltheory,autonomicnervoussystem,ventralvagalcomplex,socialengagementsystem, threatreactions,feelingsofsafety,neuroception

INTRODUCTION

Contemporarystrategiesforhealthandwellbeingfailour biologicalneedsbynotacknowledgingthatfeelingsofsafety emergefrominsidethebody.Thispaperfocusesonfeelings ofsafety,anelusiveconstructthathashistoricallybeen dependentuponsubjectivity.Itisproposedthatfeelingsofsafety haveameasurableunderlyingneurophysiologicalsubstrate. Acknowledgingthatfeelingsofsafetyareanemergentproperty ofautonomicstatewouldshiftinvestigationsoffeelingsofsafety fromasubjectivetoanobjectivescience.

Inwritingthispaper,Ihavereflectedonapersonalquestion–whatprinciplecanbeextractedfromconductingempirical researchformorethanfivedecades?Whatprinciplehas captivatedmypassionandintellectualcuriosity?Whattheme wouldIusetoorganizetheinformationfrommypapers,books, andtalks?Or,simplyphrasedwhathaveIlearned?

Afterreflectingonthisquestion,Iarrivedataconciseand intuitiveprinciplethathumans,associalmammals,areonan enduringlifelongquesttofeelsafe.Thisquestappearstobe embeddedinourDNAandservesasaprofoundmotivator throughoutourlife.Theneedtofeelsafeisfunctionally ourbodyspeakingthroughourautonomicnervoussysteminfluencingourmentalandphysicalhealth,socialrelationships, cognitiveprocesses,behavioralrepertoire,andservingasa neurophysiologicalsubstrateuponwhichsocietalinstitutions dependentoncooperationandtrustfunctionarebased.

Feelingsafefunctionsasasubjectiveindexofaneuralplatform thatsupportsbothsocialityandthehomeostaticprocesses optimizinghealth,growth,andrestoration.Operationally,feeling safeisoursubjectiveinterpretationofinternalbodilyfeelingsthat arebeingconveyedviabi-directionalneuralpathwaysbetween ourbodilyorgansandourbrain.Feelingsofsafetyarenot equivalenttoanobjectivemeasurementofsafety,whichmay pragmaticallybedefinedastheremovalofthreat.Feelingsafe ismoreakintoafeltsenseasdescribeby Gendlin (1997). AlthoughGendlin,asaphilosopherandpsychologist,wasnot physiologicallyoriented,hedescribeda“feltsense”notasa mentalexperience,butasaphysicalone.

Inunderstandingthemotivationtofeelsafe,feelingsof safetymaytobeconceptualizedfromthePolyvagalTheory. PolyvagalTheoryprovidesaninnovativescientificperspective thatincorporatesanunderstandingofphylogeneticshiftsin vertebrateneuroanatomyandneurophysiology;thisperspective identifiesneuralcircuitsthatdownregulateneuralregulationof threatreactionsandfunctionallyneutralizedefensivestrategies vianeuralcircuitscommunicatingcuesofsafety.Feelingsof safetyareoperationallytheproductofcuesofsafety,via neuroception(seebelow),downregulatingautonomicstatesthat supportthreatreactionsandupregulatingautonomicstatesthat supportinterpersonalaccessibilityandhomeostaticfunctions. Basically,whenhumansfeelsafe,theirnervoussystemssupport thehomeostaticfunctionsofhealth,growth,andrestoration, whiletheysimultaneouslybecomeaccessibletootherswithout feelingorexpressingthreatandvulnerability.

Inexplainingtheprofoundimportanceoffeelingsafe,we areimmersedintheambiguityofourlanguagewhenit

comestodescribingfeelingsandlinkingfeelingstounderlying neurophysiologicalstates.Thisproblemdatestotheearliest psychologistssuchasWundt(WundtandJudd, 1902),who adoptedandstandardizedintrospectiontechniquestoexplore sensations,whichweessentiallylimitedtoexternalstimuli. PolyvagalTheoryleadstowardahierarchicalconceptualization offeelingsashigherbraininterpretationsoftheneuralsignals conveyinginformationregardingvisceralorgans(e.g.,heart, gut,etc.)tothebrainstem.Thispsychophysiologicalperspective emphasizesthefoundationalfunctionofautonomicstateinthe subjectiveexperiencesofglobalfeelingsandspecificemotions. Withinthishierarchicalconceptualization,feelingsofsafetyare preeminentandformthecoreofanenduringmotivational systemthatshiftsautonomicstate,whichinturndrivesbehaviors, emotions,andthoughts.Theresultingmodelsuggeststhat feelingsofsafetyreflectthefoundationalautonomicstate supportingmaturation,health,andsociality.

Inanearlierpaper(Porges, 1996),ahierarchicalmodelof self-regulationwasproposedtoprovideinsightsintooptimizing interventionstrategiesforhigh-riskinfants.Themodelreflects maturationalcompetenciesinneuralregulationthatprovidea substrateforthemorecomplexco-regulatorysocialbehaviors. Themainpointofthemodelisthathigherbehavioral functions,whicharefrequentlyintentional,aredependentonthe functioningofthemoresurvivalfocusedfoundationalsystems embeddedinthebrainstem.Thelevelsaredescribedin Table1. Level1isfocusedonthefunctionofbrainstemstructures inoptimizingphysiologicalhomeostasisthroughneuraland neurochemicalbidirectionalcommunicationbetweenvisceral organsandbrainstemstructures,whichregulatetheautonomic nervoussystem.TheneuralpathwaysinvolvedinLevel1are functionalatbirthinhealthyfull-terminfants.AnindexofLevel Icanbederivedfromquantifyingrespiratorysinusarrhythmia, aperiodiccomponentofbeat-to-beatheartratevariabilitythat issynchronouswithspontaneousbreathingandavalidindexof cardiacvagaltoneviaventralvagalpathways(Lewisetal., 2012). However,inthepreterminfantthesystemisnotsufficiently mature,andtheamplitudeofrespiratorysinusarrhythmiais notabilitylow(Porges, 1992). PorgesandFurman (2011) provide amoredetaileddescriptionofthematurationalchangesinthe neuralregulationoftheautonomicnervoussystemasa“neural platform”forsocialbehavior.

LevelIIemphasizesconnectionsbetweenhigherbrain structuresandthebrainsteminregulatingautonomicstate. SuccessinLevelIIisachievedwhenthesuck-breathe-vocalize circuitisintegratedwiththeventralvagalpathway(Porges andLipsitt, 1993).Thiscircuitenablesnursingandsoothing tooccurandisdependentontheneuralpathwaysthat definetheventralvagalcomplex(Porges, 1998).Ashigher brainstructures,viacorticobulbarpathways,regulatethese brainstemnucleioftheventralvagalcomplex,thepathways aresubsequentlyrepurposedasanintegratedsocialengagement system,whichfostersocialcommunicationandco-regulation. Itisthroughtheseconnectionsthatsafetycuescanrecruit metabolicallyefficientstatesofcalmness(e.g.,slowheartrate) tooptimizehealth,growth,andrestoration.Oralternatively, threatcuescandownregulatethesocialengagementsystemto

TABLE1| Hierarchicalmodelofself-regulation(Porges, 1996).

LevelI:Neurophysiologicalprocessescharacterizedbybidirectionalcommunicationbetweenthebrainstemandperipheralorganstomaintainphysiologicalhomeostasis.

LevelII:Physiologicalprocessesreflectingtheinputofhighernervoussysteminfluencesonthebrainstemregulationofhomeostasis.Theseprocessesareassociated withmodulatingmetabolicoutputandenergyresourcestosupportadaptiveresponsestoenvironmentaldemands.

LevelIll:Measurableandoftenobservablemotorprocessesincludingbodymovementsandfacialexpressions.Theseprocessescanbeevaluatedintermsofquantity, quality,andappropriateness.

LevelIV:Processesthatreflectthecoordinationofmotorbehavior,emotionaltone,andbodilystatetosuccessfullynegotiatesocialinteractions.UnlikethoseofLevelIII, theseprocessesarecontingentwithprioritizedcuesandfeedbackfromtheexternalenvironment.

optimizemetabolicallycostlydefensivestrategies.Themetabolic requirementsforfight/flightbehaviorsrequireresourcestobe divertedfromhomeostaticfunctions.Autonomicallythisis observedthroughthedisengagementofthevagalbrake(Porges etal., 1996).Insafesocialsettingsthevagalbrakeisdynamically adjustingheartratetomatchthemetabolicneedsofthe behavior.Theabilitytodisengagethevagalbrakewhenmotor behaviors,whicharerequiredinsocialinteractions,arerelatedto subsequentcompetenciesinsocialbehavior.Morerecentlyanew metric,vagalefficiency,wasintroducedtodescribethedynamic “efficiency”ofthevagalbrake(i.e.,cardioinhibitorypathwaysto theheartmonitoredbyquantifyingtheamplitudeofrespiratory sinusarrhythmia)inregulatingheartrate.Thismetricevaluates theslopeoftheregressionlinebetweenshorttimeperiods(e.g., 15s)ofsynchronousmeasuresofheartrateandrespiratorysinus arrhythmia.Functionally,theslopeisprovidinganestimateof howmuchheartratewouldchangewithastandardizedunit changeintheamplitudeofrespiratorysinusarrhythmia.This metrichasbeenusefulinevaluatingsleepstateinfull-term newborns(Porgesetal., 1999)andthematurationaltrajectory inpre-terminfants(Porgesetal., 2019).Itisalsosensitiveto alcohol(Reedetal., 1999)andmayserveasapotentialindicator ofdysautonomia,sinceitisgreatlydepressedinindividuals withanadversityhistory(Daleetal., underreview)andin thosediagnosedwiththehypermotilitysubtypeofEhlers-Danlos Syndrome(Kolaczetal., 2021).Inthecontextofthischapter, LevelIIprovidesthefoundationalneuralplatformforfeelingsof safetyandaccesstothecircuitsthatwouldenableaneuroception ofsafety(seebelow).

Table1 emphasizesthehierarchicalnatureofspecific autonomicstatesandaccessibilityofbehaviorsthatwecluster asself-regulationskills.Theoptimalfunctionofeachlevelis contingentoneachoftheprecedinglevelsbeingadequately functioning.Observersofdevelopingchildrenareawareofthe strongmaturationalinfluencethatpushesthechildthrough thesequence.However,fewareawareoftheparallelsbetween developmentandevolutionandhowthisinformationinformsus regardingtheadaptivefunctionsofspecificautonomicstates.Itis notthataspecificautonomicstateisgoodorbad,butratherwhat adaptivefunctionsdidancestralvertebratesaccesswhilebeingin aspecificautonomicstate.

DISSOLUTION

ConsistentwithPolyvagalTheory(Porges, 2021a,b),the sequencingofthehierarchyofneuralmaturationmirrors

featuresofvertebrateevolution.Thetheoryemphasizesthe modificationsintheneuralregulationoftheautonomicnervous systemthatishighlightedthroughphylogenetictransitions, especiallythetransitionfromasocialreptilestothesocialityand co-regulationfeaturesofsocialmammals.Operationallydefining feelingsofsafetyasdependentonanautonomicstate,provides anopportunitytostudythepotentialemergentpropertiesthat aredependentonaccesstothisstate.Thus,itisproposedthat theconsequenceoffeelingsafeprovidestheneuralplatformfor cooperativebehaviors,bothsupportingphysiologicalsystems andenablingaccessibilitytohigherbrainstructuresforlearning, creativity,appreciationofaesthetics,andevenspirituality.

Anacknowledgmentofthishierarchy,resultsinquestions aboutthesequentialunfoldingofresponsestochallenges orientingwithinthebody(e.g.,feverandillness)andoutside thebody(e.g.,threat).Diseaseandinjurytothebrainhave beenobservedtodisinhibitphylogeneticallymoreancient evolutionarystructures,thatinthehealthyindividualare regulated(e.g.,inhibited)bynewerbrainstructures.Thiswas describedby Jackson (1884),whostatedthat“thehighernervous arrangementsinhibit(orcontrol)thelower,andthus,when thehigheraresuddenlyrenderedfunctionless,thelowerrisein activity.”Jacksonlabeledthisprocess,dissolution,toemphasize thatitisevolutioninreverse.

WhileJacksonemphasizedadissolutionprocessthatmirrors thereverseofevolutioninbrainstructures(i.e.,moving fromneocortextolowerbrainstructures),PolyvagalTheory emphasizesthereverseofevolutionintheneuralstructures andpathwaysthatregulatethemammalianautonomicnervous system.Inthishierarchyofadaptiveresponses,thenewest socialengagementcircuitisusedfirst;ifthatcircuitfailsto providesafety,theoldercircuitsarerecruitedsequentially.The elementsofthesocialengagementsystemarefunctionalatbirth inthefull-terminfant(see PorgesandFurman, 2011)and servetoenableinfantandmothertoco-regulateautonomic statesviareciprocalcuesofsafety.Theproductofthiscoregulationistheoptimizationofhomeostaticfunctionsenabling theinfanttomatureandthemothertorecoverfromthe metabolicallydemandingdeliveryprocess.Earlyinlifethiscoregulationprovidestheneurophysiologicalplatformformotherinfantinteractionsandattachment(Bowlby, 1988),andthe establishmentofsocialbonds,whichcanbeconceptualizedas beingdependentonassociationswithfeelingsofsafety.

FocusingonLevelsIandIIweseethatoptimalbehavior isdependenttheneuralregulationoftheautonomicnervous systemandtheconnectivitybetweencorticalareas,allowing theaccurateinterpretationofcuesofsafetyandthreat,and

thebrainstemareasregulatingtheautonomicnervoussystem. Thequantificationofrespiratorysinusarrhythmiaprovidesa quantitativeportalintoLevelI,whilethevagalefficiencymetric wouldreflectLevelIIcompetency.

AUTONOMICSTATEASAN INTERVENINGVARIABLE

Byplacingautonomicstateatthecoreoffeelingsofsafetyor threat,thepragmaticsurvivalbehaviorsoffightandflight,aswell ascomplexproblem-solvingstrategiesthatwouldleadtoescape, areconsequentialanddependentonthefacilitatoryfunctionof theANSinoptimizingthesestrategies.Similarly,turningoff threatreactionsandcalmingautonomicstate,viatheventral cardioinhibitoryvagalpathway,willpromoteinterpersonal accessibility,whilesimultaneouslysupportingtheco-regulation ofautonomicstate.Thismodelpositionsautonomicstateasan interveningvariablemediatingtheinterpretationofcontextual cuesandshapingourreactions.Withinthisconceptualization, dependingontheindividual’sautonomicstate,thesame contextualcuesandchallengesmayresultindifferentbehavioral, cognitive,andphysiologicalreactions.Forexample,recent researchdocumentsthatindicesofautonomicstateinfluenced theimpactthepandemiconmentalhealth(see Kolaczetal., 2020a),perceivedstressincollegestudents(Fanningetal., 2020),effectivenessofneurostimulationonabdominalpain (Kovacicetal., 2020),calmingbehaviorininfantsfollowing thestillfaceprocedure(Kolaczetal., 2022),andprotest behaviorsininfantsindaycaresettings(Ahnertetal., 2021). Thiswouldbetruebothwithinandbetweenindividuals(see Porgesetal., 2013).Thus,theremaybearangeofreactions amongindividualswhosharethesameenvironmentalcontext, butwhoareindifferentautonomicstates.Inaddition,the sameindividualmayalsohavearangeofreactingtorepeated exposurestothesameenvironmentalcontextthatwouldbe mediatedbyvariationsinautonomicstate.PTSDsymptoms maybetheproductofaretunedautonomicnervoussystem followingextremeand/orrepeatedexposurestothreat.Research supportstheconceptualizationthatthementalandphysical healthconsequencesofadversityarereflectedinaretuned autonomicnervoussystemlockedintostatesofdefensethat limitedanaccesstothecalmingpathwaysthroughtheventral vagusassociatedwithsociality(Williamsonetal., 2013, 2015; Kolaczetal., 2020b).

Acknowledgingtheimportantroleofautonomicstateasan interveningvariablewouldhaveprofoundconsequencesonour understandingofbehaviorandtheoften-faultyassumptionthat abehaviorisintentionalandreliablyregulatedbyrewardsand punishments.Themodelproposesthatourcognitiveintentand ourbodilystatecanpromotecompetingbehavioraloutcomes. Asanobserverofbothbehaviorandautonomicstate,mybetis onthepotencyofautonomicstate.Thisconclusionissupported bythelinkbetweenautonomicstateandfeelingsofthreatand ourembeddedbiobehavioralprogramtosurvive.Sincethese statesofdefenseareregulatedbyprimitiveneuralcircuits,circuits whicharesharedwithmanymoreancientvertebrates,intentional

self-regulationeffortsoriginatinginthecortexarefrequently ineffectiveindownregulatingsurvivaldrivenreactionstothreat, whicharedependentonlowerbrainstructures.Thesurvival programisevolutionarilyold,whiletheprogramthatturnsoff threatreactionswithcuesofsafetytopromotecalmness,sociality, andhomeostaticfunctionsisamammalianinnovationofa repurposedautonomicnervoussystemthatmaybeinfluencedby higherbrainstructures.Althoughthecalmingsystemiseffective indownregulatingthreatreactionsinresponsetomildthreats,it isdifficulttoaccesswhenthedefensivesystemsareinahighly activatedsurvivalmode.

Functionally,weneedtoconceptualizethemodelashaving bothbottom-upandtop-downpathwayswiththebottomuppathwaysbeingacombinationofbeingbothreflexive andderivativeofearlyevolutionarysurvivalprocesses.The foundationalarefunctionallyhardwiredvia“neuroception”(see below).Thus,althoughcuesofsafetyorthreatwilltrigger atop-downreflexivechangesinautonomicstate,thestates becomeassociatedwiththoughtsandbehaviors.Thisprocessis initiatedthroughinterceptionandthenbottom-upfeelingsof autonomicstateareinterpretedbyhigherbrainstructures,which inturnmayinitiateintentionalbehaviors.Thislinkagebetween feelings(i.e.,autonomicstate)andbehaviorsandthoughts formtheneurophysiologicalbasisforaspectsofassociative learning.Thepremiseofmanytherapeuticstrategiesisto separatethefeelingsfromtheassociativethoughtsandbehaviors. StrategiesthatarePolyvagal-informedfocusonenablingthe clienttoexperiencethefeelingswithoutlinkingthefeelings tothoughtsorbehaviors(see Dana, 2018; PorgesandDana, 2018).Basically,theclientlearnsthatthefeelingsarenot intentionalorundervoluntarycontrolbutarepartofanadaptive reflexivesystemthatiswiredintoournervoussystem.Thus, althoughattributesofthesequenceareinitiallyreflexive,there areeffectiveportalstomodifytheassociation.Forexample, acknowledgingthehierarchyoforganizationoftheautonomic nervoussystemwouldsuggestthattheintroductionofcues ofsafetywouldbeafunctionalantidotetothreatreactions byreducingtheassociativelinksbetweenfeelingsofthreat andthoughtsandactions.Thesespeculationsareconsistent withdissolution,aprocessinwhichthecorticalinfluenceon regulating(i.e.,calming)autonomicstatebecomelesseffective. Functionally,therepurposedneuralsystemthatemergedduring thetransitionfromancientreptilestoearlymammalsallowed socialitytofunctionasaneuromodulator,calmingphysiology andoptimizingbodilyfunctions.Inadditiontosociality,positive memoriesandvisualizationsassociatedwithpositiveexperiences enablehumanstoaccesspositivefeelings(i.e.,autonomicstate) toactivelyinhibitthreatreactions.

Accesstosocialityasaneuromodulatorisinfluencedby bothautonomicstateandtheflexibilityorresiliencethatan individual’sautonomicstatehasinreturningfromastateof threattoastatethatsupportshomeostasis.Wealsolearnthat thisaccessibilityis,inpart,dependentonapersonalhistory duringwhichautonomicstatemayhavebeenretunedtooptimize defense.Thisisfrequentlyobservedinindividualswithasevere adversityhistory,whosetraumaticexperienceshaveretunedthe autonomicnervoussystemtobelockedinstatesofdefense.

Thisisreportedbyfosterparentsofchildren,whohavebeen abusedandforsafetyconcernshavebeenremovedfromtheir biologicalparents.

CULTURALLYANDPHILOSOPHICAL INFLUENCESDIVERTINTERESTIN FEELINGSOFSAFETY

Withinoureducationalinstitutionswehavebeenacculturalized toacceptthedictumcoinedbyphilosopherReneDescartes“I think,thereforeIam”(cogito,ergosum)(Descartes, 1986).This viewhasledtoaculturalexpectationthattherationalmind definesusandthatfeelingsdistortthisexpectationandneed tobeconstrained.

PolyvagalTheoryprovidesanalternativeperspectiveto thishistoricalproposition.First,thetheorywouldleadtoa perspectivethatratherthatthinkingdefiningourexistence, feelingdoes.Specifically,arevisedPolyvagal-informedstatement wouldsuggestthatIfeelmyself,thereforeIam.Ifrequentlyuse thisexampleinmytalks,althoughIusetheFrenchandnot theLatinpresentationofthedictum.Reflexiveverbsaremore commonlyusedinFrenchthaninEnglish.Reflexiveverbsare actionsthatthesubjectisperforminguponitself.Thus,using thereflexiveformoftheverbtofeelwillunambiguouslyconvey internalfeelingsandnotthesensationsoffeeling(touching)an object.InEnglishwhenweusethewordfeel,itisambiguous andmayreflecteithersituation.Byusingjepense,doncjesuis, itiseasilyrephrasedwiththereflexiveformoftheverbtofeel. Themodifiedstatementjemesens,doncjesuisemphasizesthat ifIfeelmyself,Iexist.Astatementconsistentwiththecurrent interestinembodimentandreportsfromtraumasurvivorsof beingdisembodiedandexperiencingabodilynumbness.

Descartes’philosophyledtoapartitioningofhuman experienceintoseparatedomainsdependentonmind(mental activities)andbody(physicalstructure).Descartesproposedthat mentalstatesorprocessescannotexistoutsideofthebodyand thebodycannotthink.Theseparationbetweenmindandbody, oftenlabeledasCartesiandualism,hasbeenconsistentwithour contemporarycognitive-centricworldviewthatismirroredin acortico-centricbrain-bodyseparationthatdominatesmuchof medicalandmentalhealthtreatmentmodels.Descartesargued thatrationaledecisionmakingcanonlybedevelopedwhen judgmentsarebasednotonpassion(i.e.,bodilyfeelings).This dualismisstillprevalentincurrentmedicalpractices,especially whenillnesscannotbelinkedtoaspecificorgandysfunction. Whenobjectiveclinicalassessmentsofbodilyfluidsand/or tissuesdonotprovideapositiveclinicalindicatorleadingtoan understooddisorder,physiciansoftenassumethatthedisorder ispsychiatricorpsychosomaticandthepatientshouldget psychiatricconsultationandcare.

Accordingto Damasio (1994),Descartes’perspectivehada fatalerrorinnotacknowledgingtheinteractionoffeelings(i.e., body)withthementalactivities(i.e.,brain).Consistentwith thePolyvagalTheory, Damasio (1994) emphasizesthatbodily feelingscanhaveapowerfulinfluenceonmentalprocesses. Thus,rationalthought,asespousedbyDescarteswouldbe

aspecialcaseofmentalprocessinginwhichtheautonomic nervoussystemisnotdisruptingcognitivefunction.Perhaps,this specialcaseisdependentonanautonomicstateassociatedwith feelingsofsafety.

Culturally,wehavealsobeeninfluencedbytheconceptof survivalofthefittest.Thisconceptwasfirstintroducedby HerbertSpencer(1851).Spencerproposedthatindividualselfpreservationisthemostimportantmoralprinciple.Theterm wasthenusedbyCharlesDarwin(1859)inOntheOrigin ofSpecies.Darwinsuggestedthattheorganismsbestadjusted totheirenvironmentwerethemostsuccessfulinsurviving andreproducing.Overthedecades“survivalofthefittest”has frequentlybeeninterpretedasthestrongestandmostaggressive, whichwouldsuggestthatcontrolofresourcesandaccessto matingpartnerscouldbeanobjectivemetricoffitnessand eventuallytheproductofnaturalselection.

Inthemid-20thcentury,amoreintegratedmodelemerged thatbegantoreconcilethefindingsofgeneticsandinheritance withDarwin’stheoryanditsemphasisonnaturalselection. Theresolutionwascalledtheevolutionarysynthesisormodern synthesis,andoneofitsarchitectswasRussianpopulation geneticistTheodosiusDobzhansky.Thekeyrevelationwasthat mutation,bycreatinggeneticdiversity,suppliedtherawmaterial fornaturalselectiontoacton.Insteadofmutationandnatural selectionbeingalternativeexplanations,theywerejoinedinthis newsynthesis.Thissynthesisledtoanalternativeperspective offitness.Dobzhansky’sinsightsleadtothefollowingfrequently quotedstatementthat“thefittestmayalsobethegentlest, becausesurvivaloftenrequiresmutualhelpandcooperation” (Dobzhansky, 1962).AccordingtoDobzhansky,itisthiscapacity tocooperatethatenabledtheearliestmammalianspeciesto surviveinahostileworlddominatedbyphysicallylargerand potentiallyaggressivereptiles.

Dobzhansky’sinsightfulstatementconvergesontheemphasis ofPolyvagalTheoryonthephylogenetictransitionsin neuroanatomyandneurophysiologyassocialmammals evolvedfromasocialreptiles.Mutualhelpandcooperation aredependentonanervoussystemthathasthecapacityto downregulatethreatreactionstoallowtheproximitynecessary forcooperativebehaviorsandco-regulation.Inmammalsthis isneuroanatomicallyandneurophysiologicallyobservedinthe repurposedneuralcircuitsoriginatinginbrainstemareasthat regulatetheautonomicnervoussystem.Therepurposedsystem enablesfeelingsofsafetytoco-occurwithsociality.

THEPHYLOGENETICJOURNEY

Feelingsofsafetyformthefoundationalneuralplatformfor sociality.Throughthelensofevolution,PolyvagalTheory focusesonhowmammalsadaptedmanyofthephylogenetical ancestralstructuresthatevolvedtosupportsurvivalina hostileworld.Notethatthetitleoftheinitialpublication presentingthetheory(Porges, 1995)isasynopsisofthetheoryOrientinginadefensiveworld:Mammalianmodificationsofour evolutionaryheritage.APolyvagalTheory.Thetitlesummarizes aphylogeneticnarrativeinwhichthesurvivalofmammals

wasdependentonanabilitytodownregulateandmodifythe innatedefensivesystemsthatwereinheritedfromtheirreptilian ancestors.Theseembeddedvestigialcircuitswiththeiremergent adaptivefunctionsareembeddedinthegenesofmammals. Formammals,whosesurvivalisdependentontheirsocialityto cooperate,toconnect,andtoco-regulate(Dobzhansky, 1962),the ancientdefenseprogramshadtobeharnessedandrepurposed toenabletheexpressionofsignalsofsafetyandcalmnessin proximitytoanothertrustedmammal.

PolyvagalTheory’sinterestininvestigatingmammalian autonomicregulationfromaphylogeneticperspectivedoesnot focusontheobvioussimilaritieswithmoreancientvertebrates. Rather,itfocusesontheuniquemodificationsthatenabled mammalstooptimizetheirsurvival.Consistentwiththistheme, PolyvagalTheoryfocusesontheevolvedneuralcircuitsthat enabledmammalstodownregulatethesympatheticactivation thatcouldsupportmobilizationtofightorflee,toreduce psychologicalandphysicaldistancewithconspecifics,andto functionallyco-regulatephysiologicalandbehavioralstate.

Thetheoryfocusesonthetransitionfromreptilestomammals andemphasizestheneuraladaptationsthatenablecuesofsafety todownregulatestatesofdefense.WithinPolyvagalTheorythe evolutionarytrendhasledtoaconceptualizationofanemergent anduniquelymammaliansocialengagementsysteminwhicha modifiedbranchofthevagusisintegral.Neuroanatomically,this systemisdependentonabrainstemareaknownastheventral vagalcomplex.Thisareanotonlyregulatesthemammalian ventralcardio-inhibitoryvagalpathway,butalsoregulates thespecialvisceralefferentpathwayscontrollingthestriated musclesofthefaceandhead.Thisdoesnotprecludeother structuresfrombeinginvolvedinmammaliansocialengagement behaviorsorhomologousstructuresinothervertebrateswho donotshareourphylogenetichistorybeinginvolvedinsocial engagementbehaviors.

Therelationshipbetweenmothersandtheirnursingoffspring illustratesthesocialengagementsysteminaction.Tosurvive mammalianoffspringmustinitiallynurseastheirprimary modeofingestingfood.Tonursetheinfantmustsuck,a processdependentonabrainstemcircuitinvolvingtheventral vagalcomplex.Survivalisdependentontheinfant’snervous systemefficientlyandeffectivelycoordinatingsuck-swallowbreathe-vocalizebehaviorswithvagalregulationoftheheart throughtheventralvagalpathwaysoriginatinginthenucleus ambiguus.Throughmaturationandsocialization,this“ingestive” circuitprovidesthestructuralneuralplatformforsociality andco-regulation,asmajormediators,tooptimizehomeostatic functionsleadingtohealth,growth,andrestoration(see Porges andFurman, 2011).Formammalsthereisadependency betweenreactionstocontextualcuesandthefunctionsof thiscircuit.Cuesofthreatmaydisrupt,whilecuesofsafety maysupportorenhancefunctions.Thesensorybranchesof thefacialandtrigeminalnervesprovidemajorinputintothe ventralvagalcomplex.Functionally,changesinthestateofthis circuit,throughtheprocessofdissolution,willeitherdisinhibit phylogeneticallyolderautonomiccircuitstosupportdefense (e.g.,predator,disease,physicalinjury,etc.)orinformallaspects oftheautonomicnervoussystem,includingtheentericsystem

tooptimizehomeostaticfunction(KolaczandPorges, 2018; Kolaczetal., 2019).

Mammalsuniquelyhavedetachedmiddleearbones,which distinguishthemfromreptilesinthefossilrecord.Detached middleearbonesdelineatethefrequencybandthatenables mammalstohearspecies-specificvocalizationsassociatedwith socialcommunicationandprovidea“safe”frequencybandin whichtheycouldcommunicatewithoutdetectionbylarger predatoryreptiles.Middleearbonesaresmallbonesthatseparate fromthejawboneduringgestationaldevelopmentandform anossiclechainthatconnectstheeardrumtotheinnerear. Smallmusclesregulatedbyspecialvisceralefferentpathways travellingthroughbranchesofthetrigeminalandfacialnerves regulatethetransferfunctionofthemiddleearanddetermine theacousticpropertiesofthesoundstransducedthroughmiddle earstructuresbycontrollingthestiffnessoftheossiclechain. Whenthechainisstiff,theeardrumistighterandlowfrequency soundsareattenuated;whenthemusclesrelax,lowerfrequency soundspassthroughthemiddleearintotheinnerear.Inall mammalianspecies,basedonthephysicsoftheirmiddleear structures,thereisafrequencybandofperceptualadvantage thatisexpressedwhenthemiddleearmusclescontract(see Kolaczetal., 2018).Itiswithinthisfrequencybandthatsocial communicationoccurs,whilethelowfrequenciesthatthrough evolutionhavebeenassociatedwithpredatorsareattenuated(see PorgesandLewis, 2010).

Interestingly,thecoordinationofthecontractionand relaxationofthesesmallmusclesisfrequentlyco-regulatedwith autonomicstateandthemusclescontractwhenthereisstrong ventralvagaltonetopromotesocialcommunicationandcoregulation.Thiscoordinationbetweenlisteningtospecificsounds andautonomicregulation,providestheneurophysiological basisforsoundtocommunicatecuesofsafetyandtrust. Incontrast,whentheautonomicnervoussystemshiftstoa stateofdefensethemusclesrelax,allowingdetectionoflow frequencypredatorsounds,whichsupportdefensestrategieswith auditorycues.Inthisstate,acousticperceptionisbiasedtoward detectingcuesofthreat.

Thelinkbetweenbehavioralandautonomicstateandlistening isobviousinthestudyoflanguagedelaysandauditoryprocessing problemsinchildren.Oftenchildrenwithproblemsinauditory processingalsohavebehavioralstateregulationlimitations.This neurophysiologicallinkidentifiesapotentialportaltoregulate autonomicstatethroughacousticstimulation,whichiseasily observablewhenamothercalmsherinfantusingprosodic vocalizations.Similarly,wecanobservethispotentcalming influencewhenapetiscalmedbythevoiceofahuman.In addition,cliniciansfrequentlyreportthatsurvivorsoftrauma experienceanauditoryhypersensitivitytobackgroundsounds andanauditoryhyposensitivitytohumanvoices(Borgand Counter, 1989).Thesepointsfurthersupportthefrequently observedlinkbetweenhypersensitivityandpoorautonomic regulationreflectedinhyperarousal.

Inarecentstudy(Kolaczetal., 2022),ourresearchgroup documentedthatindividualdifferencesinmaternalvocalizations haddifferentialinfluencesoncalminginfants,followingan experimentalmanipulationknownasthe“stillface”procedure

(Tronicketal., 1978).Greatervocalprosodywasmoreeffective incalmingbehaviorandreducingheartratefollowingthesocial disruptionofthestillfaceprocedure.Ofcourse,parentsandpet ownersarefamiliarwiththeimpactoftheirvoicesoncalming theirchildrenandmammalianpets.

Basedonthislinkbetweenprosodicvocalizationsand calming,alisteningintervention,knownastheSafeand SoundProtocolTM (SSP),wasdevelopedtoreduceauditory hypersensitivities,improveauditoryprocessing,andcalmthe autonomicnervoussystem.TheSSPfunctionallyamplifiesthe embeddedprosodyinmusicbyapplyingdynamicfiltersto pre-recordedmusic.Preliminarypublicationsdocumentthe effectivenessofthisstrategy(Porgesetal., 2013, 2014).The technologyembeddedintheSSPhasreceivedthreepatentsand ismarketedbyUnyte/IntegratedListeningSystems1.Oneofthe awardedclaimsonthepatentsisfortheapplicationofthe technologyasanacousticvagalnervestimulator.

Throughtheevolutionofvertebratestherewerestrongtrends inthestructuresinvolvedinregulatingautonomicfunction. Thesetrendsmaybesummarizedasmovingfromchemical toneuralandthenevolvinggreaterspecificity,efficiency,and speedthroughfeedbackcircuitsthatreliedonmyelinated pathways.Evolutionisaprocessofmodificationinwhich existingstructuresandcircuitsaremodifiedtoserveadaptive functions.Inmammals,threeprimaryautonomicstateswith specificneuralcircuitsareobservableandemergeatdifferent timeswithintheevolutionaryhistoryofvertebrates.InPolyvagal terms,thenewestislabeledthe ventralvagalcomplex,the oldestisthe dorsalvagalcomplex,andinbetweenisthe spinal sympatheticnervoussystem.Thus,evolutioninformsusof thesequencethroughwhichthethreephylogeneticdependent circuitsregulateautonomicfunctioninresponsetosurvival driventhreatreactions.Inhumans,thissequenceisreplicated duringgestation(see PorgesandFurman, 2011).

NEUROCEPTION

PolyvagalTheoryproposesthattheneuralevaluationofrisk andsafetyreflexivelytriggersshiftsinautonomicstatewithout requiringconsciousawareness.Thus,theterm“neuroception” wasintroducedtoemphasizeaneuralprocess,distinctfrom perception,capableofdistinguishingenvironmentalandvisceral featuresthataresafe,dangerous,orlife-threatening(Porges, 2003, 2004).Aformofneuroceptioncanbefoundinvirtuallyall livingorganisms,regardlessofthedevelopmentofthenervous system.Infact,itcouldbearguedthatsingle-celledorganisms andevenplantshaveaprimordialnervoussystemthatrespond tothreat.Asmammals,wearefamiliarwithreactionstopain, atypeofneuroception.Wereacttopainpriortoourability toidentifythesourceofthestimulusorevenofanawareness oftheinjury.Similarly,thedetectionofthreatappearstobe commonacrossallvertebratespecies.However,mammalshave anexpandedcapacityforneuroceptioninwhichtheynotonly reactinstantaneouslytothreat,butalsorespondinstantaneously

1https://integratedlistening.com/porges/

tocuesofsafety.Itisthislatterfeaturethatenablesmammals todownregulatedefensivestrategiestopromotesocialityby enablingpsychologicalandphysicalproximitywithoutan anticipationofpotentialinjury.Itisthiscalmingmechanism thatadaptivelyadjuststhecentralregulationofautonomic functiontodampenthemetabolicallycostlyfight/flightreactions dependentonsympatheticactivationandtoprotecttheoxygendependentcentralnervoussystem,especiallythecortex,fromthe metabolicallyconservativedefensivereactionsofthedorsalvagal complex(e.g.,fainting,deathfeigning).

PolyvagalTheoryproposesthatneuroceptionfunctionally involvesbothtop-downandbottom-upmechanisms.The processofneuroception,consistentwithLevelIIin Table1, isassumedtobeinitiatedviatop-downpathwaysinvolving corticalareaslocatedinorneartemporalcortex,components ofthecentralnervoussystemthatreflexivelyinterpretcuesof threatandsafety.Theseareasofthecortexaresensitivetothe intentionalityofbiologicalmovementsincludingvoices,faces, gestures,andhandmovements.Embeddedintheconstruct ofneuroceptionisthecapacityofthenervoussystemto reacttotheintentionofthesemovements.Neuroception functionallydecodesandinterpretstheassumedgoalof movementsandsoundsofinanimateandlivingobjects.Thus, theneuroceptionoffamiliarindividualsandindividualswith appropriatelyprosodicvoicesandwarm,expressivefaces frequentlytranslatesintoapositivesocialinteraction,promoting asenseofsafety.Autonomicstaterespondstothetop-down detectofriskorsafety.Theautonomicreactionssendsensory informationregardingbodilyfeelingstothebrainwherethey areinterpretedandconsciouslyfelt.Thebottom-uplimbof theneuroceptionisfunctionallyequivalenttointeroception. Thus,althoughweareoftenunawareofthestimulithat triggerdifferentneuroceptionresponses,wearegenerallyaware ofourbody’sreactions(i.e.,visceralfeelings)embodiedin autonomicsignaturesthatsupportadaptivebehaviors(i.e.,social engagement,fight/flight,shutdown).

SOCIALCONNECTEDNESS:A BIOLOGICALIMPERATIVE

Abiologicalimperativeidentifiesaneedthatmustbefulfilledfor alivingorganismtoperpetuateexistenceandsurvival.Polyvagal Theorysuggeststhatsocialconnectednessisacorebiological imperativeforhumans,sincehumansurvivalisdependent ontrustedothersiswiredintoourgeneticsandisexpressed throughoutthelifespanstartingfromthemomentofbirth.

PolyvagalTheoryproposesthatsocialconnectednessis tantamounttostatingthatourbodyfeelssafeinproximitywith another.Thetheoryelaboratesthattheneuralstructuresinvolved intheSocialEngagementSystem(Porges, 2009)orchestrate theautonomicstatesoftheinteractingdyadtobothbroadcast andreceivecuesofsafetythatdownregulatethreatreactionsof defenseandpromoteaccessibilityandco-regulation.

TobesociallyconnectedviaafunctionalSocialEngagement System(Porges, 2009),commonbrainstemstructuresmust appropriatelycoordinatethestriatedmusclesofthefaceand

headwiththevagalregulationofthevisceraoriginatingina brainstemregionknownasnucleusambiguus.Interestingly, neuroanatomicallythespecialvisceralefferentpathways regulatingthestriatedmusclesofthefaceandheadoriginate andcommunicatewiththebrainstemarea(i.e.,ventralvagal complex)thatregulatetheventralvagalcardioinhibitory pathway.Theventralvagalcardioinhibitorypathwayprovides theneuralpathwaysthatareexpressedasthevagalbrakeand canbemonitoredbyquantifyingtheamplitudeofrespiratory sinusarrhythmia.

Anoptimallyresilientindividualhasopportunitiestocoregulatephysiologicalstatewithasafeandtrustedother. Ideally,the“other”personprojectspositivecuesregardingtheir autonomicstatethroughprosodicvoice,warmwelcomingfacial expressions,andgesturesofaccessibility.Fromanevolutionary perspectivetheintegrationoftheneuralregulationoftheviscera withtheregulationsofthestriatedmusclesofthefaceandhead enablevisceralstatetobeprojectedinvocalizationsandfacial expressions.Thisalsoallowsvocalizationsandfacialexpressions, modulatedbyautonomicstates,toserveascuesofsafetyor threattoothers.Togetherthesepathwaysconnectbehaviorto thenervoussystemandformthebasisforsocialcommunication, cooperation,andconnectedness.Thissystemalsoproduces,viaa ventralvagalcardioinhibitorypathway,anautonomicstatethat producesfeelingsofsafetyandreflectsanadaptivemasteryof LevelIIprocesses(see Table1).

PolyvagalTheory,byarticulatinganevolutionaryhierarchy (i.e.,basedonJacksoniandissolution)inthefunctionofthe autonomicnervoussystemtochallenges,providesaguide todynamicallymonitoradaptiveautonomicresponses.The autonomicstateofanindividual,servesasafunctionalmap ofthefoundationforemergentbehavioral,emotional,and physiologicalreactivitythatanindividualmayhaveinresponse tothreatoralternativelytopositiveexperiences.Thestateof theautonomicnervoussystemprovidesaneuralplatformforan expandedrangeoffeelingsfromthreattosafetythatprovides aneurophysiologicalsubstrateforhigherbrainstructuresto elaboratethesefeelings.Ifthefeelingsarenegativeanddependent onautonomicstatessupportingdefense,thefeelingsmayevolve intodiffusestatesofanxietyorspecificemotionssuchas fearoranger.Alternatively,ifthefeelingsarepositiveand dependentonanautonomicstateofcalmness,thusenabling interpersonalaccessibilityandco-regulation,thenthesefeelings maybeassociatedwithtrust,love,andintimacy.

CLINICALIMPLICATIONS

FromaPolyvagalperspectiveitmaybehelpfultoinvestigatehow challengesmoveusintophysiologicalstatesofthreatthatwould disruptourconnectednessandplaceourmentalandphysical healthatrisk.But,morerelevanttobothtoclientsandpersonal survival,therapistsneedtoidentifyandemphasizetheinnate resourcestheirclientshaveavailabletomitigatethepotentially devastingreactionstothreat,whichinturncandestabilizethe autonomicnervoussystem,sometimesresultinginvisceralorgan dysfunctionandcompromisedmentalhealth.

AwarenessoftheneuralsystemsunderlyingPolyvagalTheory informsboththerapistsandclientsregardingthethreatsto survivalthatcanshiftautonomicstate,movingitthrough sequentialneuralplatformsorstatesthatmimicevolutionin reverseordissolution(Jackson, 1884).Functionally,toinhibit thetrajectoryofdissolutiontocalm,wemustfirstusethe competenceofoursocialengagementsystem(auniquely mammalianmyelinatedvagalpathwayinvolvingbrainstem structuresregulatingvocalintonationandfacialexpressions) toconnectwithothersandcalmourphysiology.Without theseresources,wearevulnerabletomoveintoadaptive defensivestates.

Ourdefenserepertoireisfirstexpressedaschronic mobilizationrequiringactivationofthesympatheticnervous systemandthenexpressedasimmobilization,whichiscontrolled byanevolutionarilyolderunmyelinatedvagalpathway.Inthe absenceofanactivesocialengagementsystem,themobilized stateprovidesanefficientneuralplatformforfightandflight behaviors.Formanyindividualsthisstatewillreflectchronic anxietyorirritability.Whenmobilizationdoesnotsuccessfully movetheindividualintoasafecontext,thenthereisthe possibilitythatthenervoussystemwillshiftintoanimmobilized state.Immobilizationwithfearcanbeassociatedwithfeatures ofdeathfeigning,syncope,dissociation,withdrawal,lossof purpose,socialisolation,despair,anddepression.

Althoughbothdefensivestrategieshaveadaptivevaluesin protectingtheindividual,theyaredependentondifferentneural pathways(i.e.,highsympathetictoneorhighdorsalvagaltone). Activationofthesesystems,independentlyorsimultaneously, willinterferewithinterpersonalinteractions,co-regulation, accessibility,trust,andfeelingsafewithanotherperson.Thus, defensivestatesemergefromneuralplatformsthatevolved todefend,whilesimultaneouslycompromisingcapacitiesto downregulateourdefensesthroughthecoregulationwithasafe andtrustedindividual.Basically,thetheoryemphasizesthatin thepresenceofcuesofsafety,whichweassociatewithpositive socialinteractions,themammaliansocialengagementsystemcan downregulateourinnatereactionstothreat,whetherthethreatis tangibleandobservableorimaginedandinvisible.

STRESSANDTHREATHAVEACOMMON NEUROPHYSIOLOGICALFOUNDATION

Severalyearsago,Iwroteapaperonstressandtriedtounravel theambiguityoftheterm,especiallythecircularityofusing stressasbothastimulusandasaresponse.Nowafteralmost 30yearsseeingtheworldthroughaPolyvagalperspective,asI writeaboutsafetyandthreat,Iamremindedaboutmyearlier approachtooperationallydefinestress(Porges, 1985).Itiseasy tounderstandthattheuseofstressasaconstructisambiguous sincestresshasbeenoperationalizedtobearesponseaswellas thecontextualtriggerproducingtheresponse.Asthiscircularity isdisentangled,notethattheconceptofthreathashadascientific historysimilartostressinwhichremovalstressisconceptualized asoptimalandremovalofthreatisassumedtoproducefeelings ofsafety.Bothconstructsfocusonthenegativeattribution

ofpotentiallyobservableandquantifiablefeaturesinfluencing biobehavioralprocesses,whileoriginatingoutsideofthebody. Moreover,neitherconstructelaboratesonthemechanismsthat wouldoptimizefunctionfollowingtheremovalofstressorthreat, whileimplicitlyassumingthatremovalissufficient.

APolyvagalperspectiveshiftsthediscussionfromthe externalfeaturesdefiningstressandthreattothenervous system’sabilitytosupportordisrupthomeostaticfunctions(i.e., processessupportinghealth,growth,andrestoration).Thisnew conceptualizationwouldredefinestressasameasurablestate duringwhichhomeostaticfunctionsaredisrupted.Aredefinition wouldbeconsistentwiththedistinctionbetweenstressand copingbyemphasizingthatcopingwouldfunctionallyinclude anautonomicfeatureenablingareturntohomeostaticfunction. Itwouldalsorefinethedialogdistinguishingbetweengoodand badstressfromthestimulustotheresponse.Thus,similarto threat,stressresultsinaretunedautonomicnervoussystemto supportdefense,whiledisruptingoptimalbodilyprocesses.Ifwe assumethatremovalofstressandthreathavethesameautonomic signatureinwhichautonomicstateisdisruptedandmetabolic resourcesaredivertedfromhomeostaticfunctionstosurvival needs.Wecouldsuccinctlyproposethatfeelingsofsafetywould describerecoverytobothstressandthreat,sincefeelingsofsafety aredependentonareturntoanautonomicstatethatwould supporthomeostaticfunction.Theabilitytomove,followinga challenge,intoanautonomicstatethatsupportsfeelingsofsafety couldalsooperationallydefineresilience.

ConsistentwithCartesiandualism,thereisaninherent acceptancethattheexternaldisruptor(i.e.,stressor)canbe operationalizedandreliablyresultinameasurable“stress” response.Inthe1985paperIchallengedtheprevalentS-Rmodel, whichhadbeenfundamentaltoexperimentalscience,withan S-O-RmodelinwhichtheOororganismicstatemeasured byautonomicnervoussystemindiceswouldfunctionasan interveningvariablemediatingormoderatingtheinfluenceofS ontheR.NotethattheS-Rmodelisabehavioralrestatementof thecause-and-effectrelationshipthathasservedasthebasisof empiricalscience’squestforlawsofnature.

Becausetheinterveningvariableisassumedtobeasource ofresponsevariability,researcherswithintheexperimental laboratory-baseddisciplinesareoftenuncomfortableandseek reassuranceincomparativelysimpleinterventionsthatare relativelyindependentoftheindividualdifferencesassociated withorganismicvariables.Amongexamplesofthisapproachare manipulationsofneuralblockades(powerfuldrugsthatblock specificneuralpathways),surgicalseveringofneuralpathways, orbrainlesionsablatingspecificareasofthebrain.These manipulationsarepowerfulandtheimpactonallparticipants isrelativelysimilar.Intheanalysesofmanipulationstudies statisticallysignificanceisdrivenbytherelativechangeto themanipulationversustheindividualvariationsinresponse parametersamongsubjects.Withpowerfulinterventionsstrong relationshipsareeasilyobservedandstatisticallyconfirmed.In contrast,usingtheS-O-Rmodel,consistentwithaPolyvagal perspective,wearelookingforaninteractionthatwillinformus aboutthefeaturesthatdistinguishbetweenthosewhohavestrong orweakresponsestothesamemanipulation.

Ininterpretinginteractionswithautonomicstate(i.e.,O) ontheparametersoftheR,thereisoftenadiscomfortwithin theexperimentallaboratory-basedsciences.Thus,reporting interactionswithstatevariablesmayprovokecriticismsthat thefindingswereduetoafaultyhypothesis,poorexperimental control,inappropriatestudydesign,orayettobeidentified variable(s)influencingthegradationofreactivity.Frequentlyan alternativeplausibleexplanationthattheresponse(i.e.,effect)is notdeterministicallyrelatedtothestimulus(i.e.,cause)isnot entertained.Fortunately,withtheadventofrobustmultivariate statisticalmodels,nowthereareacceptedtechniquesthatenable researcherstoevaluatehowothervariablesmayindirectly,via interveningvariables,mediateandmoderatecause-and-effect relationships.Thesequantitativetechniqueswerenotcommonly availableduringtheearlypartofmyresearchcareer.Belowisthe introductorysegmentofthe1985paper.

Theconstructofstresshasavarietyofdefinitions.Oftenthe definitionsappearcircular,sincestresshasbeendefinedinterms ofenvironmentalstimuli(i.e.,astressingenvironment),asan organismicvulnerability(i.e.,astress-proneorganism),andasa responsetotheenvironment(i.e.,astressresponse).Theinherent circularityofthedefinitionhaslimitedthesuccinctarticulationof whatstressisandwhatcausesit.

Evenifstresswasoperationallydefinedbylabelingthestressing stimulusasthestressorandthebehavioralandphysiological responseoradaptationtothestressorasstress,atleasttwoproblems wouldremain:(1)thedefinitionsofstressandstressorwouldbe circular,and(2)therewouldbesituationsinwhichindividualand statevariablesmediateandmodulatethedegreeofresponsivityand adaptability(i.e.,stress)ofanorganismtoconstantenvironmental manipulations(i.e.,stressor).Forexample,thesameenvironmental conditionsthatmayresultinphysiologicaldebilitationforone subjectmaynotproduceadiscerniblebehavioralorphysiological responseinanothersubjectoreveninthesamesubjecttesteda secondtime.Thus,stressmustbeconceptualizednotonlyinterms ofthestressorandtheobservedresponsebutalso.Intermsofthe physiologicalstateorvulnerabilityoftheorganismatthetimeof exposuretothestressor.

Oneapproachtothecomplexproblemsassociatedwithstress researchwouldhetoreformulatetheresearchstrategy.Research isgenerallyconductedwithintheframeworkofamechanistic stimulus–response(S-R)model.Inthismodeltheresponsevariance isassumedtobedeterminedbystimulusvariance.Thus,stress responseswouldbedeterminedprimarilybythestressor.Asnoted above,however,thecharacteristicsoftheorganismatthetimeof experimentalmanipulationwouldcontributetothemanifestation ofthestressresponse.Therefore,itwouldbeexpedienttouse researchdesignsthatwouldenabletheexaminationofthestress responsenotsolelyastheproductofthestressorbutalsointerms ofthestateorconditionoftheorganismpriortothestressor. Theresearchwouldbeformulatedwithintheframe–workofa stimulus-organism-response(S-O-R)model.Thus,thechanging characteristicsoftheorganismmightindexvulnerabilitytothe stressoranddeterminethedegreetowhichtheindividualwould experiencestress.

Aswediscussstress,wenotethatexperiencesofstress andthreatappeartoreflectacommonneurophysiological platform.Substitutingthreatforstressintheaboveparagraphs

wouldresultinsimilarconclusions.Stress,similartothreat, couldobjectivelybedefinedasadisruptioninhomeostatic function.Basically,stressistriggeringabodilystateofthreat andreorganizingtheautonomicnervoussystemtopromote survival.Usingthisdefinition,wewouldbeabletodecouple goodandbadstress(e.g., McEwen, 2013)asbeingdefined bythedurationsandconsequencesofthedisruptions.Short disruptionsoracutestressfollowedbyrapidrecoverieswould functionasneuralexercisespromotingresilience.Whilemore chronicdisruptionswithoutperiodsofrecoverywouldleadto diseaseandtissue/organdamage.Researchonperceivedstress andcoping(e.g., FolkmanandLazarus, 1984)thatfocuseson copingandthelinkbetweencopingandpositiveemotionswould beconsistentwithPolyvagalTheory’semphasisonanoperational definitionofastressresponseasprolongeddisruptionof homeostaticfunctionandthepowerfulinfluenceofcuesofsafety indownregulatingthreat.

Aproblemwithusingeitherthreatorstressisthatboth constructsleadtobinary(either/or)modelsinwhichremovalof threatwouldbesufficienttofeelsafeandremovalofstresswould besufficienttooptimizehomeostaticfunctionandrelaxation. Missingisanacknowledgmentofthenervoussystem’sneed forcuesofsafetyandconnectedness.Thesemodelscouldbe reconceptualizedtoincorporateanunderstandingofsafetyand optimalhomeostaticfunction,whichmightleadtooperationally definedneurophysiologicallybasedmeasuresofrecoveryand resilience.

Othershaveproposedrelationshipsbetweensafetyandstress (Bondetal., 2010; DollardandMcTernan, 2011; Brosschot etal., 2017; Slavich, 2020)thatfocusonconstructspreviously exploredbythePolyvagalTheory(Porges, 2007).Forexample, therelationshipbetweensafetyandstressformsthebasisfor theGeneralizedUnsafetyTheoryofStress(GUTS)proposedby Brosschotetal. (2017).Althoughthetwotheoriesusedifferent termsandconstructs,thetwotheoriescanbecontrastedifwe assumethatstressandthreatresponsesareequivalent.Theinitial principleproposedinGUTSemphasizesthat“thestressresponse isadefaultresponse.”Incontrast,PolyvagalTheoryproposesthat stressisduetoadisinhibitionofasafetystateandisnotadefault state.Infact,PolyvagalTheorywouldproposethatstress(i.e., threatreactivity)ratherthanbeingadefaultstate,canbereflected intwodefensivestatesthatwouldcompromisehomeostatic functions.Thedefensivestatesadaptivelyrequirefoundational survivalorientedautonomicstatesthatdifferfromthesafestate thatsupportshomeostasis.Toshiftstates,PolyvagalTheory proposesaprocessofdissolution,triggeredbyaneuroception ofthreat,thatresultsinthedisinhibitionofevolutionarily olderneuralpathwaysthatcompromisehomeostaticfunctions toservefoundationalsurvivalneeds.ByinvokingtheJacksonian principleofdissolution,PolyvagalTheoryproposesthatstress isanadaptiveproductofthedisinhibitionofasafetycircuit thatsupportshomeostaticfunctions.Thisdisinhibitionwill occurwhensurvivalischallengedbycuesofdanger,which trigger,vianeuroception,theautonomicnervoussysteminto statesofdefense.Byacknowledgingahierarchyofautonomic statesthatparallelvertebrateevolution,thetheoryproposes adissolutionsequenceinwhichmoreancientautonomic

circuitsbecomeavailablefordefense.Thecriticalpointsare: (1)stressisnotadefaultstatebutadisinhibitionofolder survivalcircuitsresultinginshiftingtheautonomicnervous systemintostatesofdefense,(2)autonomicstatemediates thebehavioralandphysiologicalfeaturesofstressandsafety, and(3)autonomicreactivityfollowsapredictablehierarchical sequenceofdisinhibitingevolutionarilynewercircuitsinthe serviceofsurvival.

RESILIENCE:ANEMERGENT PROPERTYOFCONNECTEDNESSAND FEELINGSOFSAFETY

Recently,Iwasinterviewedforadocumentaryonresilience. Thedocumentarywasstructuredtodefineresiliencethrough thepersonalnarrativesofthreesurvivorsofsevereadversity. Myroleinthedocumentarywastoprovideacommontheme capturingtheessenceofresiliencefromaPolyvagalperspective. Thepersonalstorieswereemotionallypenetratingandreflected verydifferentexperiences.Oneintervieweesurvivedasuicide attemptbyjumpingofftheGoldenGateBridge.Herelatedthat atthemomenthejumped,heknewhehadmadeamistakeand knewhewaslovedandconnected.Hesurvivedandhasbecome anactivesuicidepreventionspeaker.Anotherintervieweewas anaward-winningchefwithanincurableinflammatorydisease thathasimpactedhereyes,skin,heart,liver,andkidneys.During thepandemic,shecontinuedtopayherstaffandusedthe remainingfoodinherrestauranttofeedthoseinneed.Thethird intervieweewasa19-year-oldcollegestudentwhocontracted flesheatingbacteria.Twiceduringtheinitialtreatments,hisheart stopped,andheneededtoberesuscitated.Theconsequenceof theinfectionwasthatbothlegsandhisfingerswereamputated. Followinghisrecoveryhereturnedandgraduatedfromcollege, climbedthehighestmountainpeakinAustralia,playsgolf,and startedafoundationtohelppeoplelikehimself.

AsIlistenedtotheirnarratives,Ifeltedhumbled.Howwould Itranslatetheircourageousactionsofsurvivalandgenerosity intobasicprinciplesthatwereembeddedinourbiology?AsI listenedtotheirstories.twoconsistentprinciplesemerged.First, theyhadaheighteneddegreeofconnectednesswithothers(e.g., family,community,andhumanity).Second,thisconnectedness shiftedthemfromaself-focusedsurvivalorientationtoaconcern forotherswithasincereneedtosupportothersthrough actionsofcompassion,benevolence,andgenerosity.Evenduring theirhealthchallenges,theyweresignalingconcernforthe caregivers’wellbeing.

ConsistentwithaPolyvagalperspective,theirsurvivalstories werenarrativesofindividualswhohadeffectivelyfulfilled theirbiologicalimperativeofconnectedness.Byintuitively connecting,theyhadtappedintoapowerfulresource,thesocial engagementsystemwithitsneurophysiologicalsubstrate,the ventralvagalcomplex.Evenduringtheprofoundchallenges oftheirillnesses,injuries,andpersonallosses,theirnervous systemsmaintainedacapacitytoconnectandtocalm.Thisstill leavestheimportantquestionofhowsomeindividualsefficiently recruittop-downmechanismseffectivelyaccessingcuesofsafety

fromcontextandmemories,whileothersdonot.Polyvagal Theorywouldproposethatthisaccessismediatedbyautonomic stateandtheefficiencyoftop-downmechanismsinregulating autonomicstate.Potentially,thismightbeindexedbythevagal efficiencymetric.

PolyvagalTheoryinformsusthatsocialityisa neuromodulatorandfunctionallysupportshomeostatic functionsthatserveasaneurophysiologicalfoundationforthe positiveemergentemotionalandsocialconsequences.Inthis paper,severalrelatedprocesseshavebeenassociatedwithfeelings ofsafetyorthreat.Inasense,wecouldsaythatPolyvagalTheory emphasizesthatresiliencereflectsaphysiologicalstate,whichis sufficientlyresilienttorecoverfromdisruptions,supportfeelings ofsafety,andconnectwithothersviaanactivesocialengagement system.Movingintothisstatehaspositiveoutcomesthatare notsolelyreflectedinsocialityandtrust,butalsoinprosocial actionsofcompassion,benevolence,andgenerositythatenable humanstoactualizetheirbiologicalimperativeofconnectedness. Thenarrativeshighlightedthepossibilitythatresiliencymight beaproductofanervoussystemwithsufficientresourcesto moveoutoftheself-orientedfocusofthreatandstresstoan other-orientedfocusoffeelingsofsafetythatnaturallyemerge intoactionsofsociality,andcompassion.

Resilienceisacomplexconstructthatappearstoembody thesuccessfulintegrationofseveralskillsandunderlying neurophysiologicalmechanismstorecoverfromseveresurvival relatedchallenges.Consideringthefocusandorganizationof thispaper,resilienceandfeelingsofsafetyshareacommon neurophysiologicalsubstrate.Onitsmostfoundationallevel, resiliencereflectsbehavioral,physiological,emotional,andsocial processesthataredependentontherecoveryofautonomic functiontoastatethatsupportssocialengagementasanadaptive strategytoco-regulatewithothersandtomutuallysupport health,growth,andrestoration.Theantithesisofresilience mightbethoughtofasbeinglockedinanautonomicstate thatwouldsupportthreatreactionswithinthebody(e.g.,injury andinfection)andfromothers.Inanautonomicstatethat supportsthreat,eventhefoundationalprocessesdescribedin LevelsIandIIin Table1 wouldbecompromised.When thesefoundationallevelsarefunctional,thenervoussystemcan supportcoordinatedgoaldirectedbehaviors.(LevelIII)and socialinteractions(LevelIV).

Anoptimallyregulatedautonomicnervoussystemwould supporthomeostasisandappropriatelyrespondtochallenges withanefficientvagalbrake(i.e.,enhancedvagalefficiency) byreactingandrecoveringtotransitorychallenges.But thesenarrativesofresilienceemphasizethatthereisamore integrativemechanisminvolvedthatislinkedtofulfillingthe biologicalimperativeofsocialconnectedness.Thiscapacityfor connectednessrequiresanactivesocialengagementsystem, whichbroadcaststheindividual’saccessibilitythroughvoice andfacialexpressivity.Inasimplisticmannerthefaceand voice,viabrainstempathwaysintheventralvagalcomplex, provideamechanismthroughwhichtheautonomicstateof twoindividualscanbesharedandfunctionallytransmitfeelings ofsafety,trust,andaccessibilitythatleadtoaneffective co-regulation.Theabilitytoco-regulateisnotsimplyacollection

ofvoluntaryoperantbehaviorsinvolvingfacialexpressions andvocalizationsbutseemstorequirethetransmissionof veridicalcuesofsafetythataresufficienttoelicitaneuroception ofsafety.Itishardtocalibratethesecues,althoughwe subjectivelyknowthroughourpersonalreactionsthatwith some,wefeelsafeandaccessible,whilewithotherswefeel uncomfortable.Ihavecometolabelpeople,whosepresence triggersasmilewithfeelingsofaccessibilityandconnection assuperco-regulators.Perhaps,resilience,asaprocess,reflects thesuccessfulbiobehavioralnavigationofthefourlevels describedin Table1 andcouldsuccinctlybesummarized asthecapacitytospontaneouslyfosterfeelingsofsafetyin bothselfandother.

CONCLUDINGREMARKS:CLAIMING OURPHYLOGENETICHERITAGE

Feelingsofsafetyplayafundamentalroleenablinghumans notonlytosurvive,buttothrive.Thissuppositionposesthe importantscientificquestionofhowafeelingcouldbeso criticaltothesurvivalofourspecies.Toanswerthisquestion, itisfirstnecessarytounderstandtherelationshipbetween feelingsofsafetyandthespecificneurophysiologicalarchitecture thatunderliesthisspecificcategoryoffeelings.Unfortunately, historicalattemptstoanswerthesetypesofquestionshavebeen elusive.Attemptstoidentifyneurophysiologicalsignaturesof specificfeelings,emotions,thoughts,orevenglobalprocesses suchassocialityhaveproduced,atbest,confusingandambiguous results(e.g., Cacioppoetal., 2000; Levenson, 2003).

Centraltothesolutionofthisproblemishowterms andconstructsareusedindifferentdisciplines.Ingeneral, attemptstotranslatefrompsychologicaltophysiological phenomenahavefocusedonastrategythatcouldbesuccinctly labeledas“psychophysiologicalparallelism.”Psychophysiological parallelismisanintriguingstrategywithastrongassumptionthat itispossibletoidentifyuniqueneurophysiologicalsignaturesof specificmentalprocesses(e.g.,feelings,emotions,thoughts,etc.). Inthe1960spsychophysiologyemergedasaninterdisciplinary sciencewithhistoricrootsembeddedinthisassumption.

AlthoughPolyvagalTheory(Porges, 1995)emerged fromtraditionalpsychophysiology,itprovidedatheoretical demarcationfromparallelism.Inasense,psychophysiological parallelismimplicitlyassumedthatoftheconstructsemployed indifferentdomainswerevalid(e.g.,subjective,observable, physiological)andfocusedonestablishingcorrelationsacross domainsthatoptimisticallywouldleadtoanobjectively quantifiablephysiologicalsignatureoftheconstructexplored inthepsychologicaldomain.Incontrast,PolyvagalTheory emphasizestheinteractiveandintegrativeaspectofdifferent levelsofthenervoussystem.Thetheoryemphasizesa hierarchicalorganizationthatmirrorsphylogeneticshifts amongvertebrates.Theevolutionarychangesarealsoreflected inmaturationaltrends.Thus,whatappearstobemore complexandrelatedtohigherbrainstructures,suchas languageandsensitivitiestoanother’sphysiologicalstatevia intonationofvoiceandgesture,isreflectingthefunctional

TABLE2| Principlesofascienceofsafety.

(1)Feelingsofsafetyareasubjectiveinterpretationofacalmautonomicstateregulatedbytheventralvagalpathwaythatsupportshomeostaticfunctions(i.e.,health, growth,andrestoration).

(2)Feelingsofthreat,stress,oranxietyaresubjectiveinterpretationsofashareddefensiveautonomicstatethatdisruptshomeostaticfunction.

(3)Feelingsofsafetyprovideaccesstothesocialengagementsystem.

(4)Whenrecruited,thesocialengagementsystemsendssignalsofsafety(e.g.,intonationofvoice,facialexpressions)toothersthatfunctionallydownregulate(via neuroception)autonomicstatesofdefensetostatesofcalmnessandaccessibilitymitigatingthemetabolicallycostlythreatreactionsthroughco-regulation.

(5)Co-regulationprovidestheneuralstatethatsupportstheestablishmentoftrustingrelationships.

(6)Autonomicstatesofcalmness(e.g.,feelingsofsafety)enableefficientaccesstothehigherbrainstructuresinvolvedinproblemsolvingandcreativity.

(7)Thereciprocalbenefitsofco-regulationformthebasisofsocialityandsupporttheneuralsystemsoptimizinghealthandperformance.

andstructuralchangesmappedintotheevolutionaryhistory ofvertebrates.Frequentlymissedwithourcortico-centric andcognitive-centricorientationistheimportanceoflower brainmechanismsinmanagingourbasicsurvival-oriented reactions.Althoughthelesscomplexearlierevolvedsystemsare oftenrepurposedinmammals,theyremainsurvivaloriented andareefficientlyavailabletosupportstatesofdefensewhen survivalischallenged.

Psychophysiologicalparallelismisfunctionallyascientific strategythatassumesanisomorphicrepresentationofa processwiththegradationsbeingmappedwithequivalent precisiononalllevels.Analternateandmoreparsimonious strategywouldbetoorganizethenervoussystemintoa hierarchicalformatinwhichneurophysiologicalprocessesrelated tobasicbiologicallydeterminedsurvivalneedsarerequired tobemanagedsuccessfullybeforehigherbrainstructuresare functionallygivenaccesstobeactivatedforproblemsolving, creativity,andevensociality.PolyvagalTheorypostulatesthat ourbiologyishierarchicallyorganizedwiththebasicsurvival needs,suchasmanaginghomeostaticfunctions,residingin foundationalbrainstemstructuresandoptimalaccessand utilizationofhigherneuralcircuitsbeingdependentonsuccess atthefoundationallevel.PolyvagalTheoryprovidesinsightsinto whatthehierarchyisandhowitcanbeidentifiedandpotentially monitored.Accordingtothetheory,thehierarchyreflectsthe phylogeneticshiftsinthenervoussystem.

Toreducetheintellectualburdenofvisualizingthe evolutionarychangesinthenervoussystem,PolyvagalTheory focusedonthephylogenetictransitionsoftheautonomic nervoussystem.Specifically,thetheoryfocusedonthefunctional consequencesofhowtheautonomicnervoussystemwas repurposedduringthetransitionfromasocialreptilestosocial mammals.Thisfocushadaserendipitousbenefit,sincethe brainstemareaisrelativelysmallandtherewassufficient comparativeneuroanatomyconductedtomapthechangesin thebrainstempathwaysandtheirpotentialadaptivefunctions. Thetheoryfocusedonhowphylogeneticchangesintheneural regulationoftheheartprovidedthefoundationalproperties forfeelingsofsafetyandemergentsociality.Thispaper emphasizesthatthesetwo“psychological”constructshavea dependenceonanevolvedlinkbetweensocialengagement behaviorsandvagalregulation.However,thereareconvergent evolutionarychangesinhowtheneuropeptidesofvasopressin andoxytocinfunctiontosupporttheadventofsocialityin mammals(Porges, 2001c; Carter, 2021).Specifically,oxytocin

playsimportantroleinregulatingtheautonomicnervoussystem enablingmammalstoimmobilizewithoutfear,givebirth,and experienceintimacywithoutrecruitingphysiologicaldefensive reactionsthroughdorsalvagalpathways(e.g.,bradycardia, syncope,anddiarrhea).

Informationfromthreescientificstrategiesleadstoan understandingofthecriticalrolethatfeelingsofsafetyplay inhumansurvival.Complementingtheevolutionaryand developmentaltrendsintroducedabovethereisathirdstrategy, anunfoldingorde-evolutionofthehierarchyinresponseto threat.Thisthirdstrategyrepresentsthestudyofpathology andadaptivereactionstochallengesincludingthreatandillness. Jackson (1884) formallyintroducedde-evolutionasdissolution toemphasizethefunctionalimpactofdiseaseordamagetothe brain.Henotedthatasevolutionarilynewercircuitsbecame dysfunctional,theynolongerinhibitedtheactionsofolder circuits,andtheoldercircuitsbecameactive.Threatisa generalizedresponsethatcanoccurinresponsetoaphysical challenge,apathogen,orevenaninaccurateinterpretationof context.Theelementsresultingathreatresponsedonothave tobevalidfromanobjectiveinterpretationofthreat.Rather, threatresponsesreflectthenervoussystemsinterpretation ofrisk.InPolyvagalterminology,threatresponsesaredue toaneuroceptionofdangerorlifethreatinwhichthe nervoussystemdeterminesriskoutsideofconsciousawareness. FromaPolyvagalperspective,threatreactionsrepresenta disruptionofhomeostaticfunctionregardlessofthevalidity ofthreat.Conversely,aneuroceptionofsafety,resultsin anautonomicstatethatsupportshomeostaticfunctionwith emergentfeelingsofsafety.

Feelingsofsafetyandthreatrecruitdifferentautonomic resourcestooptimizesurvival.However,survivalasaconstruct isoverlybroadandconfusing.Survivalcaninitiallybe deconstructedintotwodomainsofcompetence:onewithinthe bodyandtheotheroutsideofthebody.Althoughadequately respondingtobothchallengesisnecessary, internalcompetence needstoprecedeexternalcompetence.Theinternalprocesses focusonhowthenervoussystemmanagestheregulationof bodilyorgansandsupportsthebasichomeostaticprocesses ofhealth,growth,andrestoration.Thisisobviouswhen observingthechallengetosurvivalofbeingbornpremature, basicallyborntoosoonfortheirnervoussystemtoeffectively managehomeostaticdemands.Theexternalprocessesfocus onhowthenervoussystemsupportsresponsestochallenges. Forhumansthisstartswithmasteringthecoordinationof

suck-swallow-breathe-vocalizebehaviorsthatenableingestion andsocialsignaling.

Onthemostbasiclevel,feelingsofsafetyareadirectreflection ofautonomicstatewhenitisefficientlysupportinghomeostatic functions.But,thereisaconsequentialfactor.Beinginacalm autonomicstateprovidesneuralaccesstotheregulationofthe musclesofthefaceandheadthatformanintegratedsocial engagementsystem.Thissystemutilizesthesameneuralnetwork thatcoordinatessucking,swallowing,vocalizing,andbreathingat birth.Interestingly,accesstothissystemisalsoaportaltocalmas evidencedbytheoverlapbetweensocialbehaviorandingestion. Thus,feelingsofsafetynotonlyreflectacalmautonomicstate supportinghomeostaticfunctionsthatareeffectivelyregulated viatheventralvagus,butalsoprovideaccesstothespecialvisceral efferentpathwaysthatalsooriginateintheventralvagalcomplex thatenablesocialcommunication.

Frequentlymissedistheunderstandingthatthebrainstem arearegulatingtheautonomicstatethatsupportsfeelingsof safetyalsoregulatesthemusclesofthefaceandheadthat weuseforingestion,socialcommunication,andsignalingthat wecanbetrustedandaresafetoapproach.Forexample, theintonationofvoicereflectsourautonomicstate.Ifweare calmandourheartrateisslowandrhythmicallyvariable, ourvoiceisprosodic.Theintonationofvoicereflectedin prosodyistheproductofvagalpathwaysregulatinglaryngeal andpharyngealmuscles.Whenwearefrightenedorangry ourvoicelosesprosody,andourheartrateisfastandloses rhythmicvariability.Feelingsafe,bybeinginacalmautonomic state,providesaccesstoefficientlyusethesocialengagement systemandtoconveythefeelingsofsafetytoanother.This isuniversallyobservedasamothercalmsherinfantwith melodicvocalizations,gentlereassuringgestures,andwarm facialexpressions.Underlyingtheeffectivenessofthemother’s vocalizationsandfacialexpressionsincalmingtheinfantisthe factthatthesecuesofsafetyareactivelybothreflectingthe mother’sautonomicstateanddirectlyimpactingonthenerves thatregulatetheinfant’sautonomicnervoussystemviathe samebrainstemstructureslocatedintheventralvagalcomplex. However,accesstostructuresinvolvediningestionandsocial engagementbehaviorsarelimitedbyautonomicstate.These structuresareefficientlyaccessiblewhentheautonomicnervous systemiscalm,notinastateofdefense,andundertheregulation oftheventralvagalpathway.

Thispaperhasemphasizedthecommonthemethatfeelings ofsafetyreflectacorefundamentalprocessthathasenabled humanstosurvivethroughtheopportunisticfeaturesoftrusting socialengagementsthathaveco-regulatorycapacitiestomitigate themetabolicallycostlydefensereactions.Theshort-term outcomeisobviousintermsofthesupportofhomeostatic functions.However,thereisalsoalong-termconsequence offeelingsofsafetythatarereflectedintheemergence ofcommunitiesinwhichfeelingsofsafetyexpandthrough spontaneoussocialengagement.Prosocialbehaviorsamonga collectivebecomethenorm.Thus,oursocialityenablesan expansionofthosewithwhomwefeelsafeandtrust.This, ofcourse,istheunderlyingpremiseofcommunitiesincluding

legalsystems,businesstransactions,politicalnegotiations,and internationaltreaties.

Throughthestudyofneuraldevelopmentandphylogeny, wecanextractfoundationalprinciplesandtheirunderlying mechanismsthroughwhichtheautonomicnervoussystemleads tofeelingsofsafetyandopportunitiestoco-regulate.Thestudy ofmentalandphysicalillnessesprovidesaconvergentresearch strategytoconfirmtheseprinciples,sinceillnessisatriggerof dissolution,whichfunctionallydisruptsautonomicregulation andcompromisessocialengagementbehaviors.

In Table2 above,thefoundationalprinciplesareoutlined. Theprinciplessuccinctlyformahierarchythatleadstoan optimizationofhealthaswellasmental,social,andbehavioral processes.Anacknowledgmentoftheseprinciplesindaily interactionsandsocietalinstitutionswouldreinstateprocesses thatwouldsupportthequalitiesofhumanexperience,inwhich feelingsofsafetyformthefoundationofahealthierandmore productivesociety.Theseprincipleshighlightthevalidityofa scienceofsafetythatwhenimplementedinsocietalinstitutions, rangingfromhealthcaretoeducation,wouldenhancehealth, sociality,andleadtogreaterproductivity,creativity,anda senseofwellbeing.Inaway,byrespectingourneedtofeel safe,werespectourphylogeneticheritageandelevatesociality asaneuromodulatorandfunctionallyprovidethescientific validationforasocietalfocusonpromotingopportunitiesto experiencefeelingsofsafetyandco-regulation.

Insummary,feelingsofsafetyandthreataresubjective interpretationsoftheautonomicnervoussystemcommunicating viainteroceptionwithhigherbrainstructures.Ashumans, weareonalife-longquesttofeelsafe.PolyvagalTheory deconstructsthisintuitivetruthintoaplausibleneuroscience withtestablehypothesesandobjectiveneurophysiological indices.Functionally,thisquesttofeelsafeistheproduct ofrespectingtheimportantfunctionsofneuroceptionand thepowerfulroleofco-regulationandotherattributesof socialityasaneuromodulatorthatcanoptimizehealth,growth, andrestoration.

AUTHORCONTRIBUTIONS

SPcontributedtotheconceptualizationandwrote themanuscript.

FUNDING

ThisworkwassupportedbygiftstotheTraumaticStress ResearchConsortiumfromtheDillonFund,ChajaStiftung,and theUnitedStatesAssociationforBodyPsychotherapy.

ACKNOWLEDGMENTS

SpecialthanksareextendedtoSueCarterforencouragingme toformalizetheideaspresentedinthismanuscriptandforher helpfulcomments.

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