The Open Field Test

Chapter1TheOpenFieldTestToddD.Gould,DavidT.Dao,andColleenE.KovacsicsAbstractTheopenfieldtest(OFT)isacommonmeasureofexploratorybehaviorandgeneralactivityinbothmiceandrats,whereboththequalityandquantityoftheactivitycanbemeasured.Principally,theopenfield(OF)isanenclosure,generallysquare,rectangular,orcircularinshapewithsurroundingwallsthatpreventescape.Themostbasicandcommonoutcomeofinterestis‘‘movement’’;however,thiscanbeinfluencedbymotoroutput,exploratorydrive,freezingorotherfear-relatedbehavior,sickness,relativetimeincircadiancycle,amongmanyothervariables.Distancemoved,timespentmoving,rearing,andchangeinactivityovertimeareamongmanymeasuresthatcanbetabulatedandreported.Someoutcomes,particularlydefecation,centertime,andactivitywithinthefirst5minutes,likelygaugesomeaspectsofemotionalityincludinganxiety.TheOFTisalsocommonlyusedasamechanismtoassessthesedative,toxic,orstimulanteffectsofcompounds.Thus,theOFTmeasuresanumberoffacetsofbehaviorbeyondsimplelocomotion.Assuch,thetesthasanumberofusesandisincludedinalmosteverythoroughanalysisofrodentbehavior.Keywords:Activity,locomotion,exploratoryactivity,arena,anxiety,thigmotaxismouse,rodents.1.BackgroundandHistoricalOverviewTheopenfieldtest(OFT)isacommonmeasureofexploratorybehaviorandgeneralactivityinrodents,whereboththequalityandquantityoftheactivitycanbemeasured.Halliswidelycred-itedforfirstintroducingtheOFT(1,2).Whiletheoriginalstudieswereinrats,theOFThasalsobeenextensivelyusedinmice.Inadditiontototaldistancemoved,manyqualitiesofthemovementarealsoanalyzed.Theseincludetimespentalongthewalls(thig-motaxis)comparedtotimeincenter,distancemovedoverdiffer-enttimeperiods,andrearing.Additionally,theOFTissometimesusedasameanstoassessgeneralactivitylevelsasa‘‘control’’experimentforotherbehavioralteststhatinvolveactivity(3–5).T.D.Gould(ed.),MoodandAnxietyRelatedPhenotypesinMice,Neuromethods42,DOI10.1007/978-1-60761-303-9_1,ªHumanaPress,apartofSpringerScience+BusinessMedia,LLC20091TheOFTisalsocommonlyusedtoassessthesedative,toxic,orstimulanteffectsofcompounds.Assuch,thetesthasanumberofusesandisincludedinalmosteverythoroughanalysisofrodentbehavior.Principally,theopenfield(OF)isanenclosure,generallysquare,rectangular,orcircularinshapewithsurroundingwallsthatpreventescape(Fig.1.1).Thus,theOFTdoesnotgenerallyutilizea‘‘field’’inthetruesenseofawide,expansivearea,whereananimalcanmoveandbehaveunfettered,butratheranarena,thatformice,willgen-erallyvaryfrom25cm2toover250cm2.Whiletherearesomeexceptions(6),inalmostallexperimentaldesignsmiceareplacedinthearenabytheinvestigatorandthusforcedtointeractwithanovelenvironment.Thisforcedentryshouldbeconsideredwheninterpretingtheresults,asanimalsdonotactivelyseekentryintothearena.ThetraditionalOFTisbetween2and10minutesinduration.ThisshortlengthoftimeemphasizesexploratorybehaviorandFig.1.1.Examplesofopenfieldarenas.(A)Squareopenfield,100100cm.(B)Squareopenfield,5050cm.(C)Circularopenfield,250cmdiameter(photographcontributedbyDr.GregElmer,UniversityofMarylandSchoolofMedicine,MarylandPsychiatricResearchCenterandDepartmentofPsychiatry).2Gould,Dao,andKovacsicsresponsetonovelty,ratherthanbaselineactivity.Theshortlengthoftime(usedinearlystudies)wasduetomanyreasonsincludingthemethodofmanuallyacquiringdata.Morerecentapproaches,includingvideotrackingandtrackingbythenumberofinfraredbeambreaks,allowformuchhigherthroughputandlongerperiodsofmonitoring.Distancemoved,timespentmoving,rearing,andchangeinactivityovertimeareallmeasuresthatcanbetabulatedandreported(Table1.1).Therearemanyotherlesscommonlyreportedmeasuresincludingtimespentwithoutmoving,sniff-ing,vocalization,andteethchattering(seeWalshandCummins(7)forathoroughreviewofOFT-dependentmeasures).Morerecently,particularlywiththeadventofhigher-throughputmethodologyandafocusonsingleoutcomesinbehavioralstudies,therehasgenerallybeenadecreaseinthenumberofvariablesthatarereported.However,therehavebeeneffortstoincludemanyofthevariablesthatcanbeassessedbycomputersystemsincludingdarting,textureofthepathtaken,activitydensity,andprincipalcomponentanalysisincludingethologicalmeasurementsandconventionalvariables(8–12).Overall,wedonotextensivelydiscussmanyoftheselesscommonlymon-itoredoutcomesinthischapter.Furthermore,wedonotexten-sivelydiscussapproachestoconductfactoranalysisortodefinerelationshipsbetweenfactors(13).Table1.1Partiallistofcommonopen-field-dependentparametersthatcanbeassessed.Assessmentofthesemeasurescanbeastotalnumber,groupedintotimebins,ormeasuredintermsoflatency.SeeWalshandCummins(1976)(7)foranhistoricalperspectiveMovement–Distancemoved(eitheractualorrelativedistance)–Timespentmoving–Rearing(verticalactivity)–Freezing–Grooming–OtherstereotypicbehaviorsLocation–Timespentincenter–CrossesintocenterAutonomicnervoussystem–Defecation(numberoffecalboli)–UrinationTheOpenFieldTest3Themostbasicandcommonoutcomeofinterestis‘‘move-ment’’;however,thiscanbeinfluencedbymotoroutput,explora-torydrive,freezing(orotherfear-relatedbehavior),sickness,relativetimeincircadiancycle,andavarietyofothervariables.Importantly,theOFT(especi