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Touching is a powerful means for eliciting sexual arousal. Here, we establish the topographical organization of bodily regions triggering sexual arousal in humans. A total of 704 participants were shown images of same and opposite sex bodies and asked to color the bodily regions whose touching they or members of the opposite sex would experience as sexually arousing while masturbating or having sex with a partner. Resulting erogenous zone maps (EZMs) revealed that the whole body was sensitive to sexual touching, with erogenous hotspots consisting of genitals, breasts, and anus. The EZM area was larger while having sex with a partner versus while masturbating, and was also dependent on sexual desire and heterosexual and homosexual interest levels. We conclude that tactile stimulation of practically all bodily regions may trigger sexual arousal. Extension of the erogenous zones while having sex with a partner may reflect the role of touching in maintenance of reproductive pair bonds.
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IN#PRESS,#ARCHIVES#OF#SEXUAL#BEHAVIOR#
!
Topography!of!Human!Erogenous!Zones!
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Short#title:!Erogenous!Zones!
!
Lauri!Nummenmaa1-4,!Juulia!Suvilehto1,!Enrico!Glerean1,!Pekka!Santtila5,!and!Jari!K.!
Hietanen6!!
!
1Department!of!Neuroscience!and!Biomedical!Engineering!and!Computational!Science,!
School!of!Science,!Aalto!University,!Espoo,!Finland!
3Turku!PET!Centre,!University!of!Turku,!Turku,!Finland!
4Department!of!Psychology,!University!of!Turku,!Turku,!Finland!
5Department!of!Psychology!and!Logopedics,!Åbo!Akademi!University,!Turku,!Finland!!
6!Human!Information!Processing!Laboratory,!School!of!Social!Sciences!and!Humanities!/!
Psychology,!University!of!Tampere,!Tampere,!Finland!
!
!
Contact#information!
Lauri!Nummenmaa!
Department!of!Neuroscience!and!Biomedical!Engineering!!
School!of!Science,!Aalto!University!!
FI-00076!AALTO,!Espoo,!FINLAND!
Email:!lauri.nummenmaa@aalto.fi!
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# #
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ABSTRACT#
Touching#is!a!powerful!means!for!eliciting!sexual!arousal.!Here,!we!establish!the!
topographical!organization!of!bodily!regions!triggering!subjective!sexual!arousal!in!humans.!
A!total!of!participants!were!shown!images!of!same!and!opposite!sex!bodies!and!asked!to!
color!the!bodily!regions!whose!touching!they!or!members!of!the!opposite!sex!would!
experience!as!sexually!arousing!while!masturbating!or!having!sex!with!a!partner.!Resulting!
erogenous!zone!maps!(EZMs)!revealed!that!the!whole!body!was!sensitive!to!sexual!
touching,!with!erogenous!hotspots!consisting!of!genitals,!breasts,!and!anus.!The!EZM!area!
was!larger!while!having!sex!with!a!partner!versus!during!masturbation,!and!was!also!
dependent!on!sexual!desire!and!heterosexual!and!homosexual!interest!levels.!We!conclude!
that!tactile!stimulation!of!practically!all!bodily!regions!may!trigger!sexual!arousal.!Extension!
of!the!erogenous!zones!while!having!sex!with!a!partner!may!reflect!the!role!of!touching!in!
maintenance!of!reproductive!pair!bonds.!
!
Keywords:!Somatosensation;!Arousal;!Sexuality;!Touch;!Bonding!
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!!
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INTRODUCTION!
Touching!is!a!powerful!means!for!eliciting!sexual!arousal,!and!both!affectionate!
caress!from!one’s!partner!and!self-stimulation!of!the!genitals!are!capable!of!triggering!
powerful!sexual!arousal!responses.!Sexual!arousal!promotes!sexual!behavior!via!peripheral!
and!central!physiological!as!well!as!emotional!and!motivational!mechanisms!(Janssen,!
2011).!!Although!human!sexual!arousal!responses!may!be!triggered!by!visual!and!auditory!
cues,!they!are!also!driven!by!tactile!stimulation!of!the!genitals!(Steers,!2000;!Walen!&!Roth,!
1987).!This!presumably!results!from!initial!sensory!projections!from!the!external!genitalia!
relaying!multiple!sensory!qualities!to!sensory!thalamus,!periaqueductal!grey!matter,!and!
hypothalamic!sites!governing!sexual!functions!(Dean!&!Lue,!2005;!Hubscher!&!Johnson,!
2003;!Martin-Alguacil,!Schober,!Kow,!&!Pfaff,!2006),!as!well!as!from!further!interactions!
between!these!relay!centres!and!the!somatosensory!cortical!(S1)!sites!representing!the!
genitals!and!the!neural!circuitry!governing!arousal!and!reward!processing!(Georgiadis!et!al.,!
2006;!Georgiadis,!Reinders,!Paans,!Renken,!&!Kortekaas,!2009;!Komisaruk!&!Whipple,!2005).!
Consequently,!genital!stimulation,!either!by!a!partner!or!by!oneself,!is!a!common!sexual!
behavior!of!humans.!!!
Yet,!paradoxically,!tactile!stimulation!of!bodily!regions!with!no!apparent!connection!
to!the!genitals,!such!as!breasts!and!nipples,!have!also!been!found!to!trigger!sexual!arousal!
(Levin!&!Meston,!2006;!Turnbull,!Lovett,!Chaldecott,!&!Lucas,!2014)!and!consequently!
human!partners!also!caress!each!other’s!bodies!in!regions!outside!the!genitals!during!sexual!
interaction.!Together!with!genitals,!such!regions!are!often!called!!"#$!%#&'()#%!'!due!to!
their!capability!of!triggering!sexual!arousal!(Turnbull,!et!al.,!2014).!Even!though!tactile!and!
nociceptive!sensitivity!of!different!bodily!regions!is!well!understood!(Ackerley,!Carlsson,!
Wester,!Olausson,!&!Backlund!Wasling,!2014;!Mancini!et!al.,!2014),!the!quantitative!
topographical!layout!as!well!as!functions!of!human!erogenous!zones!has!remained!
unresolved.!Furthermore,!the!functional!role!of!the!arousal-triggering!properties!of!the!non-
genital!areas!is!poorly!understood.!If!sexual!touching!serves!only!a!general!arousal!
modulating!function,!touching!patterns!could!be!hypothesized!to!be!focused!on!the!genitals!
and!be!concordant!during!masturbation!and!while!having!sex!with!a!partner!because!
touching!genitals!triggers!the!most!powerful!arousal!responses!(Turnbull,!et!al.,!2014).!
However,!if!touching!the!body!during!sexual!interaction!with!a!partner!also!serves!functions!
unrelated!to!sexual!arousal,!it!could!be!hypothesized!that!the!touching!patterns!are!
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different!when!having!sex!with!a!partner!versus!masturbating.!Indeed,!humans!(Jones!&!
Yarbrough,!1985;!Willis!&!Briggs,!1992)!and!nonhuman!primates!use!touching!for!
maintaining!social!relations!(Dunbar,!2010);!thus,!it!is!possible!that!partners!having!sex!
could!extend!caresses!also!to!each!others’!non-genital!regions!to!promote!long-term!pair!
bonding!in!addition!to!triggering!and!maintaining!sexual!arousal.!!
Furthermore,!sex!differences!in!human!erogenous!zones!have!remained!
underspecified!and,!in!addition!to!trivial!differences!stemming!from!anatomy,!the!capability!
of!tactile!stimulation!of!different!bodily!regions!in!triggering!sexual!arousal!in!males!and!
females!is!not!well!understood.!Finally,!touching!a!partner!sexually!may!trigger!and!maintain!
their!sexual!arousal,!thus!preparing!the!partner!physically!for!copulation!and!promoting!
sexual!behavior.!Sexual!compatibility!with!the!partner!contributes!significantly!to!sexual!
satisfaction!and!motivation!(Hurlbert,!Apt,!Hurlbert,!&!Pierce,!2000).!Poor!communication!
regarding!sexual!matters!also!plays!a!key!role!(Purnine!&!Carey,!1997)!and!is!prevalent!
among!couples!where!the!female!partner!has!orgasmic!problems!(Kelly,!Strassberg,!&!
Turner,!2006).!It!is,!therefore,!of!interest!to!find!out!whether!men’s!and!women’s!
perceptions!of!each!other’s!erogenous!zones!correspond.!!
In!the!present!study!we!reveal!a!high-resolution!spatial!topography!of!human!
erogenous!zones!and!their!relation!to!tactile!and!nociceptive!sensitivity!using!a!novel!
computer-based!self-report!tool.!Participants!were!shown!nude!own-sex!bodies!and!were!
asked!to!color!the!regions!whose!touching!they!experience!as!sexually!arousing!when!they!
are!masturbating!or!having!sex!with!a!partner,!resulting!in!erogenous!zones!maps!(EZMs).!
To!tap!knowledge!regarding!opposite!sex!EZMs,!participants!also!repeated!the!tasks!with!
opposite!sex!bodies.!!
MATERIALS#AND#METHODS#
Participants#
A!total!of!704!Finnish!volunteers!(528!females,!*age!=!26!years,!+,-$!!=!6.5!years;!see!
Table!1!for!details)!participated!in!the!study!and!completed!the!on-line!questionnaires.!
Participants!were!recruited!from!university!email!lists!and!social!media,!and!the!study!was!
described!as!an!investigation!on!sexual!touching!on!different!bodily!regions.!An!
independent!sample!of!88!volunteers!(24!males,!*age!=!26!years)!participated!in!a!control!
experiment!mapping!tactile!and!nociceptive!sensitivity!of!different!bodily!regions.!
Participants!were!not!compensated!and!none!were!excluded!from!the!sample.!Because!
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methodologically!comparable!studies!do!not!exist,!formal!a!priori!power!analyses!were!not!
possible.!Thus,!the!sample!(targeted!700!responses)!size!was!based!on!our!previous!related!
work!on!mapping!emotional!sensations!in!the!body!(Nummenmaa,!Glerean,!Hari,!&!
Hietanen,!2014).!!
Data#Acquisition!
Background#Information#And#Questionnaires!After!providing!on-line!informed!consent,!
Participants!provided!background!information!(age,!sex,!education,!relationship!status,!
weight!and!height,!weekly!hours!spent!on!physical!exercise)!as!well!as!evaluated!how!
physically!and!sexually!attractive!they!considered!themselves!(1-10).!Female!participants!
also!reported!the!phase!of!their!menstrual!cycle!(in!days!since!the!last!menstruation!began).!
Next,!they!completed!the!following!questionnaires:!Sell!Assessment!of!Sexual!Orientation!
(Sell!1996),!Derogatis!Sexual!Functioning!Inventory!(Derogatis,!1978),!and!Relationship!
Questionnaire!(Bartholomew!&!Horowitz,!1991).!The!Sell!questionnaire!provides!
continuous,!orthogonal!estimates!of!heterosexual!and!homosexual!drive.!The!Derogatis!
inventory!indexes!actual!and!desired!frequency!of!sexual!behaviors!including!caressing,!
sexual!fantasies,!masturbation,!and!oral,!anal,!and!vaginal!sex.!The!Relationship!
Questionnaire!measures!the!perceived!quality,!closeness!and!emotional!intensity!of!the!
subject’s!current!intimate!relationship!that!are!averaged!into!one!global!score.!!
Mapping#the#Erogenous#Zones!Erogenous!zone!maps!(EZMs)!were!acquired!on-line!with!the!
!./0,1!instrument!(Nummenmaa,!et!al.,!2014;!http://becs.aalto.fi/mbl/software).!In!this!
tool!(Fig!1),!participants!were!shown!ventral!and!dorsal!views!of!bodies!of!their!own!sex,!
and!were!asked!to!color!on!separate!trials!the!regions!whose!touching!they!would!find!
sexually!arousing!while!having!sex!with!a!partner!(whose!sex!was!not!specified)!and!while!
masturbating.!To!estimate!correspondence!between!sex-specific!erogenous!zones!and!their!
estimated!distribution!by!the!opposite!sex,!participants!were!also!shown!bodies!of!their!
opposite!sex!and!this!time!asked!to!color!the!regions!whose!touching!they!thought!an!
opposite!sex!individual!would!experience!as!arousing!while!masturbating!or!having!sex!with!
a!partner.!These!opposite!sex!EZM!data!were!only!used!for!correlating!EZMs!across!sexes!
and!when!comparing!the!self-reported!EZM!area!to!opposite!sex’s!estimated!EZM!area.!All!
other!analyses!were!restricted!to!the!own!sex!EZM!data.!Paint!color!was!set!to!red!to!
maximize!visibility.!Painting!was!dynamic;!thus,!successive!strokes!on!a!region!increased!the!
opacity!of!the!paint,!and!the!diameter!of!the!painting!tool!was!12!pixels.!Erasing!paint!was!
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not!possible!but!participants!could!restart!each!trial!from!scratch!as!many!times!they!
wanted.!Finished!images!were!stored!in!matrices!where!the!paint!intensity!ranged!from!0!to!
100.!Male!and!female!bodies!were!approximately!of!similar!size!in!pixels!(*(=!53660!px).!!
To!test!for!the!relationship!between!tactile,!nociceptive,!and!sexual!sensitivity!of!
different!body!regions!empirically,!an!independent!sample!of!88!volunteers!(24!males,!mean!
age!26!years)!used!the!emBODY!tool!to!indicate,!on!separate!trials,!the!tactile!and!
nociceptive!sensitivity!of!their!different!body!regions.!The!resulting!sex-wise!mean!tactile!
and!nociceptive!sensitivity!maps!(Fig!S-1)!were!subsequently!correlated!with!the!
conditionwise!EZMs!obtained!in!the!main!experiment.!
Statistical#Analysis!
Data!were!screened!manually!for!anomalous!painting!behavior!(e.g.!drawing!
symbols!on!bodies!or!scribbling!randomly).!In!random!effects!analyses,!mass!univariate!2-
tests!were!used!on!the!subject-wise!EZMs!to!compare!pixelwise!values!for!each!condition!
against!zero.!This!resulted!in!2-maps!where!pixel!intensities!reflect!statistically!significant!
experience!of!sexual!arousal!while!touching!the!corresponding!bodily!region.!Finally,!False!
Discovery!Rate!(FDR)!correction!with!an!alpha!level!of!.05!was!applied!to!the!statistical!maps!
to!control!for!false!positives!due!to!multiple!comparisons.!EZMs!for!masturbation!versus!sex!
with!partner!conditions!were!compared!using!mass!univariate!2!tests.!Pearson!correlation!
coefficients!were!used!for!comparing!the!similarity!of!male!and!female!erogenous!zones!
reported!by!male!and!female!participants.!!
Total!area!of!erogenous!zones!was!computed!as!the!subjectwise!proportion!of!
colored!pixels;!proportional!rather!than!absolute!numbers!were!used!to!control!for!slightly!
different!number!of!pixels!in!the!male!and!the!female!bodies.!Separate!maps!were!
computed!for!own-sex!masturbation!and!sex!with!a!partner!and!opposite!sex!masturbation!
and!sex!with!a!partner!conditions.!Subsequently,!the!effects!of!participant!sex,!sexual!
behavior!and!targeted!person!(male!versus!female)!were!analyzed!with!mixed!ANOVAs.!!
Stepwise!linear!regression!analysis!was!used!to!predict!the!area!of!subject-wise!
EZMs!in!different!conditions!(masturbating!self,!having!sex!with!a!partner,!opposite!sex!
masturbating,!and!opposite!sex!having!sex!with!a!partner)!with!participants’!age,!BMI,!
marital!status,!physical!and!sexual!attractiveness,!relationship!satisfaction,!heteroesexuality!
and!homosexuality!scores!(from!the!Sell!scale)!as!well!as!estimates!of!sexual!desire!and!
activity.!
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To!characterize!in!which!order!participants!paid!attention!to!different!erogenous!
zones,!we!first!divided!both!the!dorsal!and!ventral!body!surfaces!into!seven!regions!of!
interest!(ROIs;!Fig!S-3)!and!log-scaled!total!painting!time!into!24!bins.!Subsequently,!ROI-
wise!2-values!were!computed!for!each!bin,!and!subjected!to!FDR!correction.!!!
RESULTS#
Participant!characteristics!are!shown!in!Table!1!and!correlations!between!the!
questionnaire!scores!in!Table!S-1.!Mean!EZMs!(Fig!2!and!Video!S-1)!revealed!that!for!both!
males!and!females,!erogenous!hotspots!were!focused!around!the!genitals!and!breasts,!but!
also!mouth,!buttocks,!anus,!thighs,!and!neck!were!consistently!reported!to!trigger!sexually!
arousing!sensations.!Practically!the!whole!body!was!capable!of!triggering!sexually!arousing!
sensations!when!touched,!with!only!lower!legs!and!parts!of!hands!being!left!out!of!the!
maps.!Males!and!females!also!estimated!the!opposite!sex!erogenous!zones!accurately.!
Mean!inter-sex!correlations!for!the!EZMs!were!in!general!high!(mean!"!=!0.78)!and!
responses!were!most!consistent!for!ventral!EZMs!“with!partner”!condition!(mean!"!=!0.95)!
and!least!consistent!for!dorsal!EZMs!in!the!opposite!sex!masturbation!condition!(mean!"!=!
0.35,!see!Table!2).!!
Correlating!the!EZMs!with!the!tactile!and!nociceptive!sensitivity!maps!(Fig!3)!
revealed!that!erogenous!zones!were!more!strongly!associated!with!tactile!(mean!"!=!0.64)!
than!with!nociceptive!(mean!"!=!0.37)!sensitivity!maps,!p!<!.001.!The!correlation!between!
tactile!sensitivity!maps!and!EZMs!was!stronger!in!the!sex!with!partner!condition!and!smaller!
for!the!masturbation!condition!(Fig!S-1).!!
The!EZMs!in!Fig!2!were!also!indicative!of!significant!differences!between!
masturbation!and!sex!with!partner!conditions.!This!was!confirmed!by!subtraction!analyses!
for!the!EZMs,!which!revealed!that!except!for!genitals!and!male!anus,!all!bodily!regions!were!
considered!to!trigger!stronger!arousal!when!being!touched!by!a!partner!versus!the!
participants!themselves!(Fig!4).!!
Analysis!of!the!total!EZM!area!qualified!how!the!total!area!of!erogenous!zones!was!
dependent!on!both!subject!sex!and!touch!type!(Fig!5).!A!2!(Subject!sex:!male,!female)!×!2!
(Touch!type:!masturbation,!sex!with!partner)!×!2!(Target!person:!female!versus!male)!mixed!
ANOVA!revealed!that!EZM!area!was!larger!when!having!sex!with!a!partner!than!when!
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masturbating1!F31,!702)!=!659.62,!4!<!.001,!ηp2!=!0.48,!and!EZM!area!was!also!evaluated!
larger!for!females!versus!males,!F31,!702)!=!167.89,!4!<!.001,!ηp2!=!0.10.!On!average,!26%!of!
the!female!and!22%!of!male!body!area!were!capable!of!triggering!arousal!when!touched!by!
a!partner,!whereas!corresponding!percentages!were!6.3%!and!4.3%!when!masturbating!(all!
4s!<!.001!for!between-conditions!comparisons).!Moreover,!males!estimated!EZM!areas!to!
be!larger!than!females!(mean!difference!2.64%),!F31,!702)!=!5.84!4!=!.02,!ηp2!=!0.008.!Finally,!
a!three-way!interaction!between!subject!sex,!sexual!behaviour!and!target!person,!F31,!702)!
=!16.36,!4!<!.001,!ηp2!=!0.023!revealed!that!males!overestimated!the!female!EZM!area!in!the!
masturbation!condition!(4!<!.05!Bonferroni!corrected)!whereas!male!and!female!estimates!
of!EZM!area!did!not!differ!in!other!conditions.!!
Linear!regression!analysis!(Table!3)!revealed!that!sexual!desire,!homosexual!interest,!
and!heterosexual!interest!were!the!strongest!predictors!of!the!total!EZM!area,!being!
significant!for!both!masturbation!and!sex!with!a!partner!conditions.!The!frequency!of!sexual!
activity!was!negatively!associated!with!EZM!area!in!the!masturbation!condition.!However,!
the!EZM!area!was!insensitive!to!demographic!factors,!including!age,!marital!status,!and!
education.!Separate!analysis!restricted!to!the!female!sample!found!no!effects!of!menstrual!
cycle!phase!on!the!EZM!area.!!
Finally,!a!time!series!analysis!(Fig!S-3)!confirmed!that!across!all!conditions,!
participants!first!attended!to!the!genitals,!ventral!surface!chest,!neck,!and!legs.!Other!
regions!were!attended!to!substantially!later,!yet!they!nevertheless!received!attention!earlier!
in!the!sex!with!a!partner!versus!masturbation!condition.!Early!preference!towards!genitals!
was!profound!in!males!whereas!females!attended!to!non-genital!areas!earlier!than!males.!!
DISCUSSION!
Our!findings!reveal!for!the!first!time!the!sex!and!sexual!behavior!specific!
topographical!organization!of!erogenous!zones!in!humans.!We!show!that!the!whole!skin!
serves!as!a!somatosensory!sexual!organ!for!both!males!and!females,!particularly!when!
having!sex!with!a!partner.!Although!the!erogenous!hotspots!were!located!on!core!
erogenous!zones!in!genitals,!erogenous!zones!extended!to!practically!everywhere!in!the!
body!forming!a!set!of!extended!erogenous!regions!with!second-highest!arousal-triggering!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
1 A trivial explanation for these results is that while masturbating an individual cannot touch all of their back.
However, the overall pattern of results remains essentially unchanged even when only the ventral surface of the
body is considered.
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capability!in!the!breasts!and!nipples,!anus,!buttocks,!and!inner!thighs.!The!total!bodily!area!
triggering!sexual!arousal!was!significantly!smaller!during!masturbation!versus!having!sex!
with!a!partner.!Altogether!these!findings!highlight!the!importance!of!tactile!sensation!of!
non-genital!areas!in!sexual!arousal!modulation!and!suggest!that!the!core!and!extended!
erogenous!zones!may!serve!different!functions!in!sexual!behavior!and!arousal!modulation.!!
Maps#of#Core#and#Extended#Erogenous#Zones#in#Men#and#Women#
Our!main!finding!was!that!touching!practically!all!areas!covered!by!skin!in!the!body!may!
trigger!sexual!arousal!when!touched!by!partner,!with!an!average!of!37%!of!the!total!area!
body!area!being!capable!for!triggering!sexual!arousal!upon!touch.!Males!and!females!also!
evaluated!each!others’!EZMs!similarly!(mean!"!=!0.79).!The!total!area!of!erogenous!zones!
was!larger!in!females!versus!males,!indicative!of!heightened!tactile!sensitivity!to!sexual!
touch.!This!accords!with!prior!work!using!vibro-tactile!(Gescheider,!Bolanowski,!Hall,!
Hoffman,!&!Verrillo,!1994)!and!nociceptive!stimulation!(Fillingim!&!Maixner,!1995),!which!
point!towards!higher!sensitivity!in!females!versus!males.!!
The!erogenous!hotspots!being!most!consistently!associated!with!sexual!arousal!and!
also!attended!first!were!focused!on!genitals.!Significant!EZM!peaks!were!also!observed!in!
chest,!neck,!buttocks,!anusm,!and!mouth!area!(see!Video!S-1!for!dynamically!thresholded!t-
maps)!but!also!in!some!other!regions!such!as!back,!thigh,!and!shin!that!have!low!pain!and!
tactile!sensitivity!(Ackerley,!et!al.,!2014;!Mancini,!et!al.,!2014).!However,!correlating!EZMs!
with!tactile!and!nociceptive!sensitivity!maps!highlighted!that!a!region’s!capability!for!
triggering!sexual!arousal!upon!touching!was!primarily!–!but!not!completely!–!determined!by!
its!tactile!sensitivity,!and!that!tactile!sensitivity!across!the!whole!body!is!exploited!only!
when!having!sex!with!a!partner2.!Nevertheless,!the!EZMs!bore!little!resemblance!to!the!
somatosensory!organization!of!the!body!in!somatosensory!cortices!(Penfield!&!Boldrey,!
1937;!Ruben!et!al.,!2001),!with!regions!whose!representation!is!close!to!genitals!in!the!S1!
not!being!significantly!more!prone!to!trigger!sexual!arousal!than!those!further!apart.!Thus,!it!
is!unlikely!that!partial!activation!of!the!S1!representation!of!the!genitals!by!stimulation!to!
adjacent!areas!would!be!driving!the!arousal!response!(see!also!Turnbull,!et!al.,!2014).!
However,!more!complete!understanding!of!the!somatotopic!organization!of!male!and!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
2 These maps reflect participants’ evaluation of tactile and nociceptive sensitivity, rather than true sensory thresholds.
However, the maps shown in Fig 4 agree in general well with prior studies using sparse spatial sampling of tactile sensitivity
(Ackerley, Carlsson, Wester, Olausson, & Backlund Wasling, 2014; Mancini et al., 2014).
10
female!genitals!and!erogenous!zones!in!SI!and!SII!is!needed!to!understand!the!role!of!
extragenital!regions!in!triggering!sexual!arousal.!!
The!EZMs!were!invariant!to!demographic!factors!such!as!age!and!education.!
However,!sexual!desire!as!well!as!homosexual!and!heterosexual!interest!emerged!as!
consistent!predictors!for!the!total!EZM!area!while!masturbating!or!having!sex!with!a!
partner,!suggesting!a!direct!link!between!sexual!drive!and!the!size!of!the!sexually!receptive!
field!of!the!body.!These!effects!accord!with!the!general!proposal!that!sexual!attraction!
towards!both!same!and!opposite!sex!partners!is!associated!with!sex!drive!(Lippa,!2006).!!
Sexual#and#Social#Functions#of#the#Extended#Erogenous#Zones#
Although!the!EZMs!for!the!masturbation!condition!covered!practically!all!of!the!body!
except!lower!legs,!touching!was!considered!as!sexually!arousing!in!significantly!larger!areas!
while!having!sex!with!a!partner!rather!than!masturbating!(Fig!4).!The!only!regions!more!
consistently!triggering!sexual!arousal!by!self-stimulation!versus!stimulation!by!partner!were!
the!genitals!and!male!anus!(but!see!Schober,!Meyer-Bahlburg,!&!Dolezal,!2009!for!opposite!
findings).!Masturbation!occurs!frequently!in!both!human!and!nonhuman!primates!even!
when!opportunities!for!copulation!exist!(Ford!&!Beach,!1951;!Oliver!&!Hyde,!1993)!and!male!
masturbation!(leading!to!ejaculation!and!wasting!of!sperm)!across!a!variety!of!species!has!
been!proposed!to!increase!sperm!fit!without!increasing!the!number!of!sperm!in!the!female!
tract!(Baker!&!Bellis,!1993).!Against!this!background,!different!goals!of!masturbation!versus!
having!sex!with!the!partner!could!explain!this!difference:!Stimulation!of!the!sexually!most!
sensitive!regions!during!masturbation!would!be!an!effective!way!of!obtaining!sexual!release,!
as!no!excess!energy!is!wasted!on!stimulating!the!sexually!less!sensitive!regions.!This!
however!raises!the!question!why!the!–!seemingly!less!sexually!sensitive!–!areas!outside!
genitals!are!stimulated!during!sex!with!a!partner.!
The!reason!for!the!lack!of!self-produced!tactile!stimulation!outside!the!genitals!could!
be!that!sensation!of!self-produced!touch!is!simply!attenuated.!A!forward!model!
incorporating!motor!actions!predicts!their!sensory!consequences!and!leads!to!sensory!
attenuation!of!self-produced!tactile!stimulation!in!the!somatosensory!and!insular!cortices!
(see!review!in!Blakemore,!Wolpert,!&!Frith,!2000).!Such!attenuation!may!tone!down!the!
arousal!responses!triggered!by!self-touch,!consequently!lowering!the!incentive!motivation!
for!extragenital!touching!during!masturbation.!While!such!attenuation!for!self-stimulation!
seems!to!occur!almost!everywhere!in!the!body,!it!was!markedly!absent!in!the!genital!region!
11
and!participants!consistently!reported!higher!arousal!ratings!for!touch!on!genitals!in!the!
masturbation!versus!sex!with!partner!condition.!Different!forward-model!attenuation!
patterns!across!SI!regions!representing!the!genitals!versus!other!bodily!regions!could!
explain!the!heightened!sensitivity!for!self-touching!on!the!genitals,!in!order!to!enable!self-
stimulation!potentially!increasing!reproductive!fit!(Baker!&!Bellis,!1993).!!!
However,!the!forward!model!attenuation!does!not!explain!567!humans!experience!
sexual!arousal!when!their!partners!touch!less!sexually!sensitive!bodily!regions!while!having!
sex!together.!From!the!perspective!of!energy!expenditure,!it!would!be!beneficial!to!restrict!
mutual!touching!to!the!genital!regions!while!having!sex!with!a!partner!as!well.!A!possible!
explanation!is!that!stimulating!these!areas!by!touching!promotes!non-sexual!aspects!of!
partnership,!such!as!pair!bonding.!Abundant!evidence!suggests!that!both!humans!(Jones!&!
Yarbrough,!1985;!Willis!&!Briggs,!1992)!and!nonhuman!primates!use!social!touching!or!
grooming!for!reinforcing!social!structures!(Dunbar,!2010).!Translational!work!shows!that!
slow!stroking!of!the!hairy!(but!not!glabrous)!skin!stimulates!the!slow-conducting!
unmyelinated!c-tactile!fibres!(CTF),!subsequently!projecting!insular!(but!not!somatosensory)!
cortices!and!possibly!providing!the!sensory!pathway!for!emotional!and!affiliative!touching!
(Loken,!Wessberg,!Morrison,!McGlone,!&!Olausson,!2009;!Olausson!et!al.,!2002).!Affiliative!
touching!and!stimulation!of!the!CTF!may!support!maintenance!and!establishment!of!long-
term!relationships!in!humans!as!well!(Dunbar,!2010).!In!line!with!this,!intimate!touching!is!
typically!restricted!to!the!closest!relationships!only!(Jones!&!Yarbrough,!1985;!Willis!&!
Briggs,!1992),!and!quality!and!quantity!of!social!touching!is!positively!associated!with!
relationship!satisfaction!in!couples!(Hertenstein,!Verkamp,!Kerestes,!&!Holmes,!2006).!
Because!c-tactile!receptors!have!not!been!found!in!genitalia,!it!is!unlikely!this!pathway!plays!
a!role!in!triggering!of!arousal!by!touching!of!the!genitals!(Liu!et!al.,!2007).!We!thus!propose!
that!touching!on!glabrous!non-genital!regions!during!sexual!interaction!with!a!partner!could!
serve!a!double!function:!stimulating!the!fast-conducting!myelinated!afferents!projecting!to!
S1!and!via!interaction!with!thalamic!arousal!circuits!serves!to!trigger!sexual!arousal,!
whereas!simultaneous!stimulation!of!the!slow-conducting!CTFs!could!promote!affiliation!
and!long-term!pair!bonding!between!the!partners.!!
Potential#limitations#and#future#directions#
It!must!be!noted!that!our!study!was!based!on!self-reports;!hence,!the!data!may!not!
directly!translate!to!different!bodily!regions’!capabilities!in!triggering!physiological!sexual!
12
arousal!when!touched.!However,!given!the!consistent!association!between!self-reported!
and!physiologically!measured!emotional!(Lang,!1995)!and!sexual!arousal!(Chivers,!Seto,!
Lalumiere,!Laan,!&!Grimbos,!2010),!it!is!feasible!to!assume!that!the!findings!reflect!
physiological!sexual!arousal!reasonably!accurately.!The!study!participants!were!recruited!
from!Finland.!Even!though!the!biologically!based!sexual!sensitivity!of!different!bodily!
regions!is!likely!culturally!universal,!in!future!it!will!be!interesting!to!address!what!kinds!of!
sexual-response-specific!plasticity!the!tactile!systems!may!exhibit!in!different!cultures!and!
sexual!preferences.!!Finally,!future!studies!need!to!disentangle!the!sexual!sensitivity!of!
specific!parts!of!the!genitalia!(such!as!vulva!versus!clitoris),!as!this!was!beyond!the!spatial!
resolution!of!the!current!study.!!
Conclusions#
We!conclude!that!the!whole!human!body!supports!triggering!of!sexual!arousal!by!
somatosensory!stimulation.!There!is!a!clear!topographical!organization!of!the!core!and!
extended!zones!with!differential!arousal-triggering!capabilities.!The!core!regions!show!high!
sensitivity!to!self-touch!during!masturbation!as!well!as!to!external!touching!while!having!sex!
with!a!partner,!yet!the!extended!regions!are!selectively!sensitive!to!externally!produced!
stimulation.!We!propose!that!this!selectivity!of!the!extended!erogenous!zone!reflects!its!
role!in!establishment!and!maintenance!of!pair!bonds,!highlighting!the!role!of!
somatosensory!system!and!sexual!behavior!in!human!social!interaction.!!
! !
13
Acknowledgements:#This!research!was!supported!by!Academy!of!Finland!(MIND!program!
grants!#265915!to!LN!and!#266187!to!JKH).!!
#
Conflict#of#interest:!The!authors!declare!no!competing!financial!interests!
!
!#
!
!
! !
14
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17
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!
! !
18
#
Figure#1.!Data!acquisition!with!the!emBODY!tool.!!
!
# #
19
#
Figure#2.!Maps!of!human!erogenous!zones!during!masturbation!and!sex!with!a!partner.!The!
data!are!thresholded!at!p!<!.05,!FDR!corrected.!The!colorbar!indicates!the!t-statistic!range!in!
one!sample!test.!!
!
# #
20
#
Figure#3.#Mean!tactile!and!nociceptive!sensitivity!maps!for!males!and!females.!The!data!are!
shown!on!an!arbitrary!scale![0,!1]!and!are!square!root!transformed!to!better!visualize!
regional!variation!in!the!lower!tail!of!the!distribution.!!
!
# #
21
#
Figure#4.!Subtraction!contrasts!for!the!erogenous!zones!in!the!partner!versus!masturbation!
condition.!White!outline!shows!regions!where!the!opposite!contrast!(masturbation!versus!
partner)!was!significant.!The!data!are!thresholded!at!p!<!.05,!FDR!corrected.!The!colorbar!
indicates!the!t-statistic!range!in!a!paired!samples!test.!!#
#
# #
22
#
Figure#5.!Effects!of!participant!sex!and!touch!type!(masturbation!vs.!sex!with!partner)!on!the!
total!area!of!erogenous!zones!in!the!male!and!female!body!averaged!across!ventral!and!
dorsal!surfaces.!Error!bars!show!standard!errors!of!mean.!Touching!conditions!with!different!
letters!are!significantly!different!at!p!<!.05,!and!asterisks!denote!conditions!with!significant!
sex!differences!at!p!<!.05.!All!multiple!comparisons!are!Bonferroni!corrected.!#
! !
23
Table#1.!Participant!characteristics.!!
Males!(n!=!176)!
Females!(n!=!528)!
!
*(
+,(
*(
+,(
4-value!
28.05!
8.26!
25.11!
5.56!
***!
35.00!
!
27.00!
!
ns.!
20.00!
!
26.00!
!
ns.!
29.00!
!
36.00!
!
ns.!
16.00!
!
11.00!
!
ns.!
3.03!
2.12!
3.23!
2.23!
ns.!
6.90!
1.36!
6.90!
1.51!
ns.!
6.39!
1.68!
6.66!
1.70!
ns.!
3.81!
2.92!
4.29!
2.78!
*!
5.53!
1.35!
5.16!
1.39!
**!
4.03!
1.10!
3.76!
1.02!
**!
0.42!
0.97!
0.78!
0.94!
**!
3.23!
1.22!
2.85!
1.00!
***!
!
Note.!***!=! p!<! .001,!**! =!p! <!.01,! *!=! p!<! .05!in! two-sample!t-test! or!proportions! test!for!
categorical!variables!between!males!and!females.!
# #
24
Table#2.#Pearson!correlations!between!EZMs!estimated!by!male!and!female!participants.!!
Condition#
r"
Female!ventral!with!partner!
0.95!
Female!dorsal!with!partner!
0.95!
Male!ventral!with!partner!
0.92!
Male!dorsal!with!partner!
0.91!
Female!ventral!masturbation!
0.85!
Male!ventral!masturbation!
0.78!
Female!dorsal!masturbation!
0.59!
Male!dorsal!masturbation!
0.35!
Note.#The!correlations!represent!the!pixelwise!similarities!between!averaged,!conditionwise!
EZMs!for!male!and!female!participants.!All!shown!correlations!are!significant!at!p!<!.05.!
#
!
# #
25
Table# 3.!Model! fits,!coefficients! of!determination!(in! %)!and! betas!for!variables! predicting!
total!area!(%)!of!erogenous!zones!while!masturbating!and!having!sex!with!a!partner.!!
!
!
F#
R2#
Sexual#
desire#
Sell#
HMSX#
Sell#
HESX#
Sexual#
activity#
Masturbating!
14.59***!
8%!
0.11**!
0.24***!
0.10*!
-0.13**!
Sex!with!partner!
19.01***!
8%!
0.12**!
0.20***!
0.10*!
!
!
Note.!***!=!p!<!.001,!**!=!p!<!.01,!*!=!p!<!.05!
#
#
!
... Several of these extra-genital erogenous zones are capable of eliciting sexual arousal when stimulated, sometimes even eliciting orgasm (Younis, Fattah, & Maamoun, 2016). These areas can encompass up to 26% of the body surface (Nummenmaa, Suvilehto, Glerean, Santtila, & Hietanen, 2016) and are reported as arousing in the large majority of individuals (Younis et al., 2016). To date, only a small number of studies (Nummenmaa et al., 2016;Turnbull, Lovett, Chaldecott, & Lucas, 2014) have systematically mapped the tactile erogenous zones of the body. ...
... These areas can encompass up to 26% of the body surface (Nummenmaa, Suvilehto, Glerean, Santtila, & Hietanen, 2016) and are reported as arousing in the large majority of individuals (Younis et al., 2016). To date, only a small number of studies (Nummenmaa et al., 2016;Turnbull, Lovett, Chaldecott, & Lucas, 2014) have systematically mapped the tactile erogenous zones of the body. Across these studies, several extra-genital body parts were reliably identified as capable of eliciting high levels of sexual arousal: these included the breasts, nipples, lips, neck and nape of neck, ears, buttocks, and inner thigh (Nummenmaa et al., 2016;Turnbull et al., 2014;Younis et al., 2016). ...
... To date, only a small number of studies (Nummenmaa et al., 2016;Turnbull, Lovett, Chaldecott, & Lucas, 2014) have systematically mapped the tactile erogenous zones of the body. Across these studies, several extra-genital body parts were reliably identified as capable of eliciting high levels of sexual arousal: these included the breasts, nipples, lips, neck and nape of neck, ears, buttocks, and inner thigh (Nummenmaa et al., 2016;Turnbull et al., 2014;Younis et al., 2016). The topographical distribution and intensity of erogenous zones are similar for men and women (Nummenmaa et al., 2016;Turnbull et al., 2014) and are relatively impervious to sociological, demographic, and cultural factors (Turnbull et al., 2014). ...
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... The sexual cues of vision, audition, and even fantasy can trigger sexual arousal, but the tactile stimulation of the genitals is still the most potent sensation. After analyzing the erogenous zones of 704 Finns (including 176 men), Nummenmaa et al. (43) found that the genital area is one of the most consistent regions to cause excitement, whether it is in sexual intercourse with a partner or masturbation, and is even more sensitive during the masturbation. The deficiency of GS inhibits sexual arousal and reduces the frequency of sexual activity (44). ...
... After SCI, adaptive and compensatory changes occur in the patient's sexual sensory function due to impaired or missing GS. Residual sexual sensation becomes more sensitive, some secondary sensitive areas (lips, nipples, etc.) are strengthened, and new sexually sensitive areas (neck, ears, etc.) appear above the level of injury (6,43). This makes discovering and developing substitute erogenous zones a feasible way to promote the patients' sexual satisfaction. ...
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... In humans, copulatory acts are often preceded by tactile stimulation not involving the genitals. Mechanical stimulation of the skin, particularly in the pectoral area in women as well as of both ends of the digestive canal in men and women seem to be efficient stimuli for further enhancement of general arousal and sexual motivation (Nummenmaa et al., 2016). We propose that general arousal is the main contributor to the increase in sexual excitation. ...
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... Additionally, female passengers are more likely than men to touch the driver's unclothed nipple. This was a curious finding, as nipples can be highly erogenous zones for both women and men, but typically more so for women (Misery & Talagas, 2017;Nummenmaa et al., 2016). Thus, it would be reasonable to expect females to engage more in nipple self-touch. ...
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... Interestingly, the results of the study showed that CT-optimal touch was able to convey arousal, lust and desire while affiliative emotions (such as love and social support) were induced by general pleasant touch, regardless the velocity of stroking. As to the stimulated body area, the genitals generally have the highest erotogenic potential 6,47,49,51 . However, whether CT afferents, expected to be present in the hairy skin only 52 , are present in the genitals is unknown 53 . ...
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Preprint
The endogenous mu-opioid receptor (MOR) system modulates a multitude of social and reward-related functions, and exogenous opiates also influence sex drive in humans and animals. Sex drive shows substantial variation across humans, and it is possible that individual differences in MOR availability underlie interindividual of variation in human sex drive. Here we measured healthy male subjects’ ( n =52) brain’s MOR availability with positron emission tomography (PET) using an agonist radioligand, [ ¹¹ C]carfentanil, that has high affinity for MORs. Sex drive was measured using self-reports of engaging in sexual behaviour (sex with partner and masturbating). Bayesian hierarchical regression analysis revealed that sex drive was positively associated with MOR availability in cortical and subcortical areas, notably in caudate nucleus, hippocampus, and cingulate cortices. These results were replicated in full-volume GLM analysis. These widespread effects are in line with high spatial autocorrelation in MOR expression in human brain. Complementary voxel-based morphometry analysis ( n =108) provided limited evidence for association between sex drive and cortical density in the midcingulate cortex. We conclude that endogenous MOR tone is associated with individual differences in sex drive in human males.
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