Carnal pleasures

Carnal

pleasures

Lauri

Nummenmaa

and

Lotte

van

Dillen

Pleasuresaretightlyintertwinedwiththebody.Enjoyment derivedfromsex,feedingandsocialtouchoriginatefrom somatosensoryandgustatoryprocessing,andpleasant emotionsalsomarkedlyinfluencebodilystatestiedtothe reproductive,digestive,skeletomuscular,andendocrine systems.Here,wereviewrecentresearchonbodilypleasures, focussingonconsummatorysensorypleasures.Wediscuss howdifferentpleasureshavedistinctsensoryinputsand behaviouraloutputsandreviewthedataontheroleofthe somatosensoryandinteroceptivesystemsinsocialbonding. Finally,wereviewtheroleofgustatorypleasuresinfeedingand obesity,anddiscusstheunderlyingpathophysiological mechanisms.Weconcludethatdifferentpleasureshave distinctinputsandspecificoutputs,andthattheirregulatory functionsshouldbeunderstoodinlightofthesespecific profilesinadditiontogenericrewardmechanisms.

Addresses

1

TurkuPETCentre,UniversityofTurku,Finland

2_{DepartmentofPsychology,UniversityofTurku,Finland} 3_{TurkuUniversityHospitalUniversityofTurku,Finland} 4_{PsychologyInstitute,LeidenUniversity,TheNetherlands} 5_{LeidenInstituteforBrainandCognition,LeidenUniversity,The}

Netherlands

Correspondingauthor:vanDillen,Lotte(dillenlfvan@fsw.leidenuniv.nl)

CurrentOpinioninBehavioralSciences2021,39:85–92

ThisreviewcomesfromathemedissueonEmotion,motivation, personalityandsocialsciences*PositiveAffect*

EditedbyGillesPourtois,DisaSauter,BlairSaundersandHenkvan Steenbergen

https://doi.org/10.1016/j.cobeha.2021.02.026

2352-1546/ã2021TheAuthors.PublishedbyElsevierLtd.Thisisan openaccessarticleundertheCCBYlicense(http://creativecommons. org/licenses/by/4.0/).

Introduction

Pleasureisaninherentlycarnalexperience.Enjoyingsex

or cuddly comfort withour partnernecessitates mutual

touching and caressing. Delights of a savoury meal are

dependent on the gustatory senses, and the thrills of

physicalexerciseliterally requirethatwe putourwhole

bodies into motion. Once triggered, pleasures also

markedly alter our bodily states: sexual arousal rapidly

increases blood flow in the genitals, feeding triggers a

complexcascadeofcentralandperipheralneurohormonal

signalling,andexerciseswitchesourskeletomuscularand

cardiovascular systems into top gear. It comes as a no

surprisethatthewayweuseourbodiesinthelongterm

alsocausallyaltersourmoods.Regularstrenuousphysical

exercise improves mood while concomitantly lowering

stress, depression, and anxiety levels[1]. On theother

hand, unhealthylifestyle choices, for example,habitual

overeatingleadingtoobesity,constitutesariskfactorfor

mooddisorders [2],andalmosthalf ofpatientsmeeting

criteriaformedicalweightmanagementalsomeetcriteria

for mood disorders or other psychiatric conditions [3].

Even pleasures that are less directly tied to allostasis

involvethebodyinmanyways.Wederiveawidevariety

ofpleasuresfromsimplyperceivingothers’bodies,

rang-ingfromsexualarousaltriggeredbynudity[4]toaesthetic

appreciationof paintingsthatengagessensorimotor

net-worksinadditiontolimbicandparalimbicrewardcircuits

[5],tothechillsinducedbymusic [6].Here,wereview

theroleofsomatosensation,interoceptionandgustation

across different pleasures in both healthy subjects and

patients. Wediscuss how recentfindings point to

fine-grained granularityin thebodilybasisofdifferent

plea-sures, focussing on consummatory sensory pleasures

derivedfromsociability andfeeding.

Specificity

of

bodily

pleasure

responses

Humansexperiencepowerfulhedonicbodilysensations

rangingfrom satietytosexual arousal,buthowspecific

are the underlying physiological responses? There has

been an ongoing debate regarding the specificity of

bodily profiles ofdifferent emotions,with some

meta-analysessupporting[7]andothersfailingtodifferentiate

between them, not even between pleasure and other

emotions[8].Alikelyreasonforthelownettspecificity

isthelowdimensionalityofthemeasured

psychophysi-ological signals. The most widely used electrodermal

measures and electrocardiogram typically index

unspe-cific ANSactivity, thusfailingto capture morespecific

autonomic differences between i) emotionsand ii)

dif-ferent positiveemotionsandpleasures.However,

exist-ingstudiespointtowardsclearphysiologicaldifferences

across different types of pleasure states. For example,

simple readouts of ghrelin, leptin, and insulin levels

provide an accurate estimate of hedonic eating, that

is, for the food’s gustatory and rewarding properties

[9] yet these endocrine responses are uncoupled from

sexual arousal. Subjective sexual arousal — be it

trig-geredbyvolitionalthoughtsorautomaticallyby

percep-tion ofsexualcues —in turnis consistentlyassociated

with autonomically governed genital responses [10].

Autonomic indices of sexual arousal (penile/vaginal

from other pleasures [11], with likely no discernible

effectsonleptin,ghrelin orinsulinlevels.

Although physiologically unspecific, analysis of simple

self-reports of phenomenological bodily sensations has

establishedthatdifferentemotionshavediscernibleand

consistent ‘feeling signatures’ in the body [12,13].

Importantly, pleasure is one main determinant of the

organization of bodily sensation patterns, yet different

pleasuresfeelmarkedlydifferentinthebody (Figure1)

suggesting fine-grained organization of somatosensation

andinteroceptionassociatedwithdifferentpleasure

sys-tems.Moreover,themorepleasurableamentalor

homeo-static feels, the more strongly it is experienced in the

bodyandinthemind[12],indicatingastrongtendency

forpleasurestooverrideourconsciousstreamofthought

and behaviour.Thesemaps are also consistentacross a

widerange of Western European (WC)and East Asian

(EA) cultures, and independent of subject sex [14],

pointing to their biological rather than acquired origin.

Together with data from other modalities [15] these

self-reportbodymappingdataclearlysuggestthat

differ-entpleasuresarebynomeansaunifiedphenomenonin

thehumanbody.Thus,althoughmeta-analysesshowthat

all distinct pleasures involve the mesolimbic reward

system(ventromedialprefrontalcortex,ventralstriatum,

amygdala,anteriorinsulaandmediodorsalthalamus)ina

comparablefashion[16],differentpleasureshavedistinct

inputs(gustatoryforfeeding,tactileforsexual,

interocep-tiveandprocioceptiveforphysicalexerciseandsoforth)

andspecificoutputs(e.g.thedigestivesystem,the

geni-tals, specific musclegroups, etc.).Accordingly,detailed

understandingofthespecificbodilyinputsandoutputsof

differentpleasuresiscriticalalsoforunderstanding

plea-sure-relatedpathologies, as we will illustrate further in

ourdiscussionof humantouchandfeeding.

Touch,

somatosensation,

and

pleasure

Touchingisoneofthemostpowerfulwaysof

communi-catingpositiveaffect,andhumansandotherprimatesuse

touchingforbothtriggeringsexualarousalandpromoting

interpersonal bonds. Postnatal skin-to-skin contact

Figure1

Pride Relaxation Succeeding Wanting Orgasm Craving

Feeling

touch Gratefulness

Winning Laughing Happiness Pleasure Love Sympathy

Sexual arousal Social closeness 1 0 Effect size

Current Opinion in Behavioral Sciences

promotesbondingbetweenmotherandinfant,andboth

thequalityandquantityofromantictoucharepositively

associated with relationshipsatisfactionin couples [17].

Human skin is broadly tuned for sensing pleasurable

touch [18],and pleasure triggered by socialtouching is

an important mediator of social bonding. The closer

someoneistousinoursocialnetwork,themorepleasant

theirtouchfeels[19].Inaseriesofstudies,wehavealso

shown thatthehuman body contains finelytuned

rela-tionship-specific touch allowance maps that determine

whereothermembersofoursocialnetworkcantouchus.

ThesemapsareconsistentacrossWesternEuropeanand

EastAsiancultures,andinallculturesthebrevityofthe

touchallowancezonesinthebodyislinearlydependent

on the emotional bond between the toucher and the

individualbeingtouched[19,20].Thecloseremotional

bond two individuals have,the more pleasant touching

feels and the larger area is allowed for social touch

(Figure 2).

Some aspectsregarding thesocial relationshipwith the

toucherarecarriedalreadyintheprimarysomatosensory

cortex (S1), and these relationship-specific activation

patterns canbe resolvedfromBOLD-fMRIsignal with

machinelearningalgorithms[21].Theseeffectscouldbe

argued to reflect differencesin touch kinematicsacross

individuals, yet similar effects are also observed when

subjectsareledtobelievethatasingletoucherisoneof

two differentidentities[22].Pharmacologicalstudiesin

nonhuman primates [23] suggest that the endogenous

mu-opioidreceptor(MOR)systemmediatesthecalming

effectsofaffiliativetouching,althoughcontradictory

evi-dencealsoexistsforhumans[24].Yet,because

interindi-vidual differences in MOR availability are linked with

attachment security and prosociality [25], variation of

MORs may constitute a risk for psychiatric morbidity.

In line with this, socioemotional life history also has a

causalroleinaffectivecommunicationwithtouch.

Child-hoodmaltreatmentisassociatedwithbothaltered

inter-personaldistancepreferenceandneuralandexperiential

processingofsocialtouch,whichmaybothconstituterisk

factors for interpersonal dysfunctions and psychiatric

disorders[26].

Pleasurable social touching is conveyed by the

slow-conducting unmyelinated c-tactile fibers projecting to

theinsularcorticesbutnottoS1,andc-tactilefibershave

longbeenconsideredtheprimarypathwayforconveying

affiliativetouch[27].Accordingly,patientswith

fibromy-algiaratebothslow(CT-optimal)andfast

(CT-subopti-mal) brushingas lesspleasantthanhealthy participants,

andduringfMRIthesepatientsalsoshowdeactivationin

theright posteriorinsula whileevaluatingthe

pleasant-ness of touch.This suggestsdecouplingbetween

early-stagesensoryandevaluativeprocessingofaffectivetouch

[28].Although CT-optimalslow stroking or pettinghas

longbeenconsideredastheprimarymechanismof

affili-ate touching,hugging andmassagingmightalso convey

social proximitybetweenindividuals.One recent study

found thatdeeppressurestimulationakin tohugging is

experienced as pleasant and calming,and it also yields

comparable brain activation as CT-optimized slow

Figure2

(a) (b)

Pleasure Pleasure

Emotional bond Emotional bond

Current Opinion in Behavioral Sciences

Socialbondingwithtouchingisculturallyuniversal.Pleasurecausedbysocialtouchingislinearlydependentonthestrengthoftheemotional bondwiththetoucherinawiderangeofWesternEuropeanandEastAsiancultures(A).PanelBshowsdefactorelationshipsbetweentoucher andthetouchedpersonsfordatathatareaveragedacrosscountries.RedrawnfromRefs.[19,20].

stroking[29].Bothhealthycontrolsandautistic

individ-ualsalsofinddeeptouchpressurecalmingand

comfort-ing, even though the latter may dislike CT-optimized

stroking [30]. This suggests fine-grained distinctions

between different tactile sensory pleasures, although

someaspectsoftheneuralcodingofthepleasuremight

becomparable.

Touchingisalsothemostpotentwayforincreasingsexual

arousal,andbothself-stimulationandpartners’caressescan

elicitandmaintainasexualarousalstate.Yet,thereisno

evidence of CT innervation in the genitalia, thus, this

pathwaylikelydoesnotplayaroleintriggeringofarousal

bytouchingofthegenitals[31],againsuggesting

elemen-tary physiological differences even in different tactile

pleasures suchas pleasant sexualandnon-sexual touch.

Thisfitswithrecentworkonhumanerogenouszones[18]

that establishedthat sexual self-stimulationis primarily

focusedonthegenitalregions(withhighestself-reported

tactilesensitivity),whilesexualtouchfrompartnersisalso

distributedoverareaswiththec-tactilereceptorsinvolved

inemotionalbonding(Figure3a).Thus,mutualtouching

onthenon-genitalareasduringsexwithapartnerservesnot

justsexual, but also bonding motives.Indeed, although

self-reportedtactileandnociceptivesensitivitypeakinthe

genitalarea,significantlylargerareasofthebodyhavehigh

hedonicsensitivity,possiblypertainingtotheirCT

affer-ents(Figure3b)andreflectingtheroleoftheseinputsin

socialbonding.

Feeding

and

gustatory

pleasures

Whenhungeriswrenchingourstomach,thefirstbitesofa

deliciousmealmaybringusimmensedelight.Yet,

plea-suresandhomeostaticbalancearenotperfectlycoupled.

Eating a satiating yet unpleasant-tasting meal after an

overnightfastingmay actuallydecreasepleasure,despite

leadingtoanimprovementinthecurrentmetabolicstate

and insulin signalling[32]. Conversely, feeding for just

pleasureincreases peripherallevelsof the‘hunger’

hor-moneghrelinmorethan feedingformaintainingenergy

homeostasis [9,33]. Ghrelin influences signalling in the

VTA, which increases food intake and expression of

m‑opioidreceptors(andsubsequentresponsestosucrose

andchowintake).Abulkofstudieshavealsofoundthat

Figure3

(a) Women Men (b) Hedonic Tactile Nociceptive

Masturbating With partner Masturbating With partner sensitivity sensitivity sensitivity

FDR 35 0 10

Back

Front

Current Opinion in Behavioral Sciences

Pleasuremapsinthebody.Sex-specifictopographyofhumanerogenouszoneswhilemasturbatingandhavingsexwithpartner(a),andhedonic, tactile,andnociceptivesensitivitymapsofthehumanbodyaveragedacrosssexes(b).AdaptedfromRefs.[18,20].

glucose tasting based signalling isan important

compo-nentin generatingthesatietyresponse[34].Thiscould

explain the counterintuitive finding that replacing

glu-cose with artificial sweeteners may lead to weight gain

despite loweredenergy intake: Weakening the

associa-tion between sweet taste and post-ingestive outcomes

mightimpairweightregulation[35]asanindividualcan

nolongeranticipatewhencaloriesareactuallyconsumed.

Inline withthis,sucralosefailstoengagedopaminergic

midbraincircuitssimilarlyassucrose[36],whilebariatric

surgerydecreasespreferencesforsucrose[37].And

tax-ingpeople’smentalcapacitysuppressestasting[38],but

increases consumption, of particularly high-rewarding

sweet and salty products [39], which concurs with less

effectivecouplingbetweenprimaryinsularandsecondary

orbitofrontaltasteprocessing areas[40].

Numerous neuroimaging studies show that feeding

stronglyengagesthebrain’srewardcircuit[41]and,with

positron emission tomography studies implicating

involvement of both opioidergic[42]and dopaminergic

[43]componentsoftherewardsystem(Figure4).Inline

with this, opiate addicts experience sweetness as more

pleasant than drug-naı¨ve controls, while opioid

antago-nists decrease rewarding properties of sugar in heroin

addicts [44]. Also, in healthy humans, opioid agonist

morphine increasesand antagonistnaltrexonedecreases

theperceivedsweetnessofsucrosesolutions[45].

Accord-ingly, repeatedoverstimulation of thereward circuitby

overeating in obesitycanlead to avicious circle where

high-energy hedonicfoodintakeisconstantlyincreased

to compensate for receptor downregulation, leading to

weight gain. Illustratingthis point,theabove-described

decreasesin likingfor mixtureswithhigh-sucrose—or

high-fatcontentfollowingbariatricsurgery,concurswith

enhanced neuralresponses to ‘sweet’ and ‘fat’ in brain

regions implicated in taste and reward [37]. Finally,

weightlossfollowingbariatricsurgeryrapidlynormalizes

MOR levels (in 6mo) in morbidly obese patients [46],

suggesting a causal role of overweight in MOR

down-regulation.However,suchpromisingoutcomesarepartly

clouded bythe fact that humans have thetendency to

compensatelackofpleasureinonedomainwithpleasure

in another. For example, a substantial proportion of

patientsundergoingbariatricsurgery forobesity—thus

physicallyrestrainingthecapacityforfeeding—develop

a alcohol or substance use disorder [47]. This suggests

thattacklingpathologicalhedonicconsumptionby

rein-ingtherewarddriveandconsummatorypleasurecouldbe

problematic, as itdisregards humans’ seemingly

unlim-itedappetiteforpleasures,inparticularduringthe

refrac-torypost-consummatory period.

Dysregulation

of

pleasure

in

the

body

Carnalpleasuresarestrongmotivatorsforadaptive

behav-iour.Theyensurethatourbodilyneedsrelatedto

homeo-stasis, reproduction and safety are fulfilled even when

conflictinggoalsexist.Conversely,manybodilypleasures

may be hampered by concomitant bodily displeasure.

This is most salient in the link between chronic pain

anddepression[48],butalsoinhealth-relatedbehaviors.

Forexample,initialpainandnegativefeelingsassociated

with trainingmaydiscourage individualsfrominitiating

routine physical exercise, although repeated physical

exercise will shift the resultant mood from displeasure

to pleasure[49].Manybodilypleasuresserveimportant

functions,butseekingthemmayalsotriggercompulsive

consumption leadingto obesity and substance use

dis-orders(SUDs).Dysregulatedstriataldopamineand

opi-oid signaling and hypoactive inhibitory circuits in the

Figure4

(a)

Dopamine release

Opioid release

BOLD-fMRI response

Current Opinion in Behavioral Sciences

Brainresponsestobodilyconsummatoryreward.Endogenousdopamine(A)andopioid(B)releasetriggeredbyfeedingasindexedwith neuroreceptor-PET,and(C)meta-analysismapofBOLD-fMRIresponsestoviewingoreatingfoods.AadaptedfromRef.[43],Badaptedfrom Ref.[32]andCretrievedfromtheNeuroSynthdatabaseonOctober7th2020.

frontal cortex are hallmarks of both SUDs and obesity

[50]. Whereas substances of abuse likewise are not

neededforanythingexceptthetemporarypleasuresthey

generatetheydodirectlytapintoallostaticsystemsthat

yieldreliablepleasuresensations,suchthatespeciallyin

heavyaddictions,thesecanevenbe‘hacked’atthecostof

morenaturaltriggers likefoodandbonding [51,52].

Self-reportdatashowsthatthestrongerbodilyresponsesa

psychologicalorsomaticstatetriggers,themoresaliently

it is experienced in the phenomenological awareness

[12].Accordingly,itispossiblethatstrongbodily

sensa-tionsassociatedwithhedonicconsumptionarecriticalfor

the development of addiction-like behaviours. Indeed,

most drugs with high abuse potential (ranging from

nicotine to alcohol, heroine and amphetamine) trigger

strongbodily sensationswhen consumed. Interestingly,

thereisapaucityofpatientcaseswithreportedaddictive

or compulsive behaviour towards non-carnal pleasures

such as aestheticexperiences derived from music,

lan-guage, or art. Although the reason for this remains

unknow,itispossiblethatthesepleasuresrelyonhighly

contextual/learned,complex cognitions[53] thatdonot

consistentlyyielda bodilyresponse, thus making them

unlikely targets of addictions via the somatic feelings

linkedwith rewardconsumption.

Conclusions:

moving

beyond

a

generic

pleasure

state

Weconcludethatalthoughdifferentpleasuresmayhavea

partiallyshared neuralbasis [16], theyalso haveclearly

distinct sensory inputsand somatic and behavioral

out-putsthat,sofar,remainpoorlyunderstoodwithinwider

frameworksofcandidatepleasuresystems.Although

dif-ferentpleasuresinvolvediscretebodilyexperiences,the

specific bodily response patterns across different

plea-sures remain poorly characterised [8], and we are not

aware of studies that have compared the somatic basis

of different positive emotions using a systematic and

high-dimensionalsampling framework. Inthe future,it

is necessary to go beyond simple low-dimensional

psychophysiological measurements (ECG,skin

conduc-tance)and performcarefuldelineationusinglarge-scale

neurohormonal kits and actual whole-body metabolic

imagingduring different pleasure states. Recent

devel-opments in nuclear medicine imaging allow fast

fre-quencyreadouts(1Hz)thatactuallyallow directinvivo

molecularimagingofemotion-relatedbodilyphenomena

[54]. Finally, whereas carnal pleasures are less

contin-gent on learning — already neonates show adult-like

responses to pleasurable stroking in somatosensory and

limbicemotioncircuits[55],thebodilybasisof‘complex’

pleasures more dependent on learning are not equally

wellunderstood.Although,as notedalready,somesuch

bodilysignaturessuchaspleasurablechillstriggeredwith

musichavebeenestablished[56],thisremainsan

under-exploredfield.Whereasitisimportanttokeepexamining

commonalities across different pleasures, studying

distinct pleasure profiles mayprove just as informative

for advancing theory. This calls for a detailed ‘carnal

taxonomy’of pleasures,throughaunifiedapproachthat

goes beyondneuroimaging and involves detailed

endo-crinological, psychophysiological and subjective

mea-suresofthesedifferentpleasures.

Conflict

of

interest

statement

Nothingdeclared.

Acknowledgements

ThisstudywassupportedbytheAcademyofFinland(grants#294897and #332225),SigridJuseliusStiftelseandSigneochaugustGyllenberg’s stiftelseandtheDutchResearchCouncil(OpenResearchAreagrant #464-18-105).

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