Perceived social isolation and cognitionJohn T. Cacioppo and Louise C. Hawkley

Center for Cognitive and Social Neuroscience, University of Chicago, 5848 S. University Avenue, Chicago, IL 60637, USA

Review

Social species, from Drosophila melanogaster to Homosapiens, fare poorly when isolated. Homo sapiens, anirrepressibly meaning-making species, are, in normalcircumstances, dramatically affected by perceived socialisolation. Research indicates that perceived social iso-lation (i.e. loneliness) is a risk factor for, and may con-tribute to, poorer overall cognitive performance, fastercognitive decline, poorer executive functioning,increased negativity and depressive cognition, heigh-tened sensitivity to social threats, a confirmatory biasin social cognition that is self-protective and paradoxi-cally self-defeating, heightened anthropomorphism andcontagion that threatens social cohesion. These differ-ences in attention and cognition impact on emotions,decisions, behaviors and interpersonal interactions thatcan contribute to the association between lonelinessand cognitive decline and between loneliness and mor-bidity more generally.

IntroductionThe health, life and genetic legacy of members of socialspecies are threatened when they find themselves on thesocial perimeter. Social isolation decreases lifespan in thefruit fly [1]; promotes obesity and Type 2 diabetes in mice[2]; exacerbates infarct size and edema and decreases post-stroke survival rate following experimentally inducedstroke in mice [3]; promotes activation of the sympatho-adrenomedullary response to an acute immobilization orcold stressor in rats [4]; delays the effects of exercise onadult neurogenesis in rats [5]; decreases open field activity,increases basal cortisol concentrations and decreaseslymphocyte proliferation to mitogens in pigs [6]; increasesthe 24 h urinary catecholamines levels and evidence ofoxidative stress in the aortic arch of rabbits [7]; anddecreases the expression of genes regulating glucocorticoidresponse in the frontal cortex of piglets [8]. Humans, bornto the longest period of abject dependency of any speciesand dependent on conspecifics across the lifespan to sur-vive and prosper, do not fare well either, whether they livesolitary lives or simply perceive that they live in relativeisolation (Box 1).

Perceived social isolation, known more colloquially asloneliness, was characterized in early scientific investi-gations as ‘a chronic distress without redeeming features’(p. 15) [9]. Recent research suggests that the social pain ofloneliness evolved as a signal that one’s connections toothers are weakening and to motivate the repair andmaintenance of connections to others that are needed forour health and well being and for the survival of our genes(Box 2) [10]. Experimental, cross-sectional and longitudi-

Corresponding author: Cacioppo, J.T. (jcaciopp@uchicago.edu)

1364-6613/$ – see front matter � 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tics.2009.0

nal studies are beginning to elucidate the various ways inwhich loneliness is related to, and in some cases affects,human information processing.

Cognitive capacitiesHuman social processes were once thought to have beenincidental to learning and cognition, whereas the socialcomplexities and demands of primate species are nowthought to have contributed to the evolution of the neo-cortex and various aspects of human cognition. Consistentwith this reasoning, human toddlers and chimpanzeeshave similar cognitive skills for engaging the physicalworld but toddlers have more sophisticated cognitive skillsthan chimpanzees for engaging the social world [11]; cross-species comparisons have revealed that the evolution oflarge and metabolically expensive brains is more closelyassociated with social than ecological complexity [12]; anda composite index of sociality in troops of baboons has beenfound to be highly correlated with infant survival [13].

Evidence that social isolation might be related to funda-mental aspects of cognition comes from animal researchshowing that isolation impairs learning that requires theinhibition of previously learned responses (e.g. reversallearning, extinction) [14] and from human research show-ing that loneliness is a risk factor for cognitive decline [15–

17] and Alzheimer’s disease (AD) [17]. Gow and colleagues[17] investigated the correlates of changes inmental abilityof 488 individuals from the Lothian Birth Cohort Studywho were tested at age 11 and 79. Among the variablestested were loneliness, social support and social network(e.g. presence of significant others, number of significantothers). After controlling for age-11 IQ, gender, years ofeducation and social class, only loneliness was associatedsignificantly with changes in IQ. Although loneliness istemporally stable and heritable [18,19], the study by Gowand colleagues does not address the possibility that lone-liness is a consequence rather than a predictor of cognitivedecline. Two recent longitudinal studies do address thisquestion.

Tilvis and colleagues [15] measured cognition by themini-mental state examination and the Clinical DementiaRating at baseline and at one-, five- and ten-year assess-ments of a population-based sample of 75–85-year-oldindividuals. Results at the 10-year follow-up assessmentrevealed APOE4, elevated serum (ionized) calcium andloneliness independently predicted cognitive decline.Wilson et al. [16], in a larger prospective study, assessed823 older adults (Mage = 80.7 years, SD = 7.1) free ofdementia at enrollment. Participants completed an exten-sive battery of cognitive measures to assess global cogni-tion, episodic memory, semantic memory, workingmemory, perceptual speed and visuospatial ability. The

6.005 Available online 31 August 2009 447

Box 1. Physiological and health effects

Although objective social isolation can affect loneliness [55,56],

perceived social isolation (loneliness) is more closely related to the

quality rather than quantity of social interactions [55]. This is in part

because loneliness is influenced by factors unrelated to objective

isolation, including genetics [57], childhood environment [18],

cultural norms [58], social needs [59], physical disabilities [55] and

discrepancies between actual and desired relationships [60]. Accord-

ingly, perceived social isolation predicts various outcomes above

and beyond what is predicted by objective isolation. For instance,

loneliness predicts elevated blood pressure [61], morning rise in

cortisol [36], reduced physical activity [62], perceptions of the

neighborhood environment as unsafe [63], and changes in life

satisfaction across a lifetime [17] beyond what could be predicted by

social support or objective social isolation. In studies of cognitive

functioning, Wilson et al. [16] found no evidence for an influence of

social network size or frequency of social activity on cognitive

decline or on risk for AD, whereas loneliness persisted in predicting

each of these outcomes even when social network size and

frequency of social activity were statistically held constant. Similarly,

loneliness has been found to predict lifetime change in IQ [17] and

changes in depressive symptoms [39] beyond what could be

predicted by objective isolation. Experimental manipulation of

loneliness [30] and imagined future isolation [64] result in cognitive

changes even though objective isolation is not altered in these

experimental studies. Perceived (but not objective) social isolation

has even been associated with gene expression—specifically, the

under-expression of genes bearing anti-inflammatory glucocorticoid

response elements and over-expression of genes bearing response

elements for pro-inflammatory NK-kB/Rel transcription factors

(Figure I) [37]. This finding is paralleled by decreased lymphocyte

sensitivity to physiological regulation by the hypothalamic pituitary

adrenocortical (HPA) axis in lonely individuals [65], which together

with evidence of increased activity of the HPA axis [24,66,67],

suggests the development of glucocorticoid resistance in chronically

lonely individuals. We, therefore, focus the current review on the

association between perceived social isolation and cognition.

Figure I. Differential gene expression in individuals high versus low in loneliness. Genome-wide transcriptional profiles were assessed in peripheral blood leukocyte

RNA samples collected from individuals in the top and bottom 15% of the distribution of subjective social isolation. Analysis by Affymetrix U133A high-density

oligonucleotide arrays identified 209 transcripts showing >30% difference in mean expression levels across groups (green = over-expression in high-lonely,

red = under-expression). High subjective social isolation is associated with a statistically significant net reduction in the number of expressed genes (131 down-

regulated versus 78 up-regulated, p value by exact binomial test). (From Ref. [37])

Review Trends in Cognitive Sciences Vol.13 No.10

lonelier the participants were, the poorer the cognitiveperformance within each of these domains at baseline,and loneliness was associated with greater cognitivedeclines in every domain except working memory andepisodic performance. Furthermore, 76 individuals devel-oped dementia during the 65-month study period. Coxproportional hazards models that controlled for age, sexand education indicated that loneliness significantlyincreased the risk of clinical AD, and this associationwas unchanged when objective social isolation and otherdemographic and health-related factors served as covari-ates. Wilson et al. [16] also examined the possible role ofdepressive symptoms because depression can also contrib-ute to cognitive decline. The loneliness at baseline pre-dicted cognitive decline and the onset of AD even whendepressive symptoms served as a covariate. For instance,the association between loneliness and AD risk was

448

reduced by about 16% when controlling for depressivesymptoms and remained significant. Depressive sympto-matology, by contrast, wasmarginally related to the risk ofAD and this association was reduced by more than halfwhen controlling for loneliness (see also Hertzog et al.) [20].

Brain autopsies were available for 67% of the partici-pantswho died during the study; of these, 30%had a clinicaldiagnosis of AD. Loneliness and the neuropathologicalmeasures derived from the brain autopsy were each inver-sely related to global cognition at the last assessment priorto death, but loneliness was unrelated to the neuropatho-logical measures. Although the mechanism underlying theassociation between loneliness and cognitive decline has notyet been identified, social isolation was recently shown todecrease central anti-inflammatory responses and survivalrate, and increase the infarct size and edema development,following the induction of stroke in mice [3]. The deficits in

Box 2. A biological signal to renew the connections needed to survive and prosper

The species Homo sapiens is fundamentally social, and in ontogeny

and phylogeny humans need others to survive and prosper. Physical

pain is an aversive signal that evolved to motivate one to take action

to minimize damage to one’s body. Loneliness, a social pain, is an

aversive signal that evolved to motivate one to take action that

minimizes threats or damage to one’s social body. Research on social

rejection, for instance, suggests that social pain co-opted physical

pain to extend its protective function to include those with whom we

form connections. In Eisenberger, Lieberman and Williams’ study

[68], participants were excluded from or included in a social situation

(i.e. a ball tossing game). Results revealed neural activation localized

in a dorsal portion of the anterior cingulate cortex (dACC) that is

implicated in the affective component of the physical pain response.

Eisenberger and her colleagues suggest that ‘Because of the adaptive

value of mammalian social bonds, the social attachment system-

. . .may have piggybacked onto the physical pain system to promote

survival’ (p. 291).

Loneliness also appears to modulate the rudimentary reward

system to extend its protective function to social cognition and

emotion. The ventral striatum, a key component of the mesolimbic

dopamine system, is rich in dopaminergic neurons and is critical in

reward processing and learning [69,70]. The ventral striatum is

activated by primary rewards such as stimulant drugs [71], absti-

nence-induced cravings for primary rewards [72] and secondary

rewards such as money [73]. Evidence that social rewards also

activate the ventral striatum has begun to accumulate in studies of

romantic love [74], social cooperation [75], social comparison [76] and

punitive altruism [77]. Cacioppo and colleagues [78] investigated how

an individual’s loneliness was related to the differential activation of

the ventral striatum to pleasant social versus matched nonsocial

images. As depicted in Figure II, lonely individuals showed a weaker

activation of the ventral striatum to pleasant pictures of people than

to equally pleasant pictures of objects, whereas nonlonely individuals

showed a stronger activation of the ventral striatum to pleasant

pictures of people than to objects. Experience sampling studies

confirm that lonely individuals regard pleasant interpersonal interac-

tions to be less pleasant but less so than do nonlonely individuals

[31].

Figure II. A cluster of voxels centered in the ventral striatum, but extending to the amygdala and portions of the anterior thalamus, showed an inverse relationship

between loneliness and activation in the pleasant social–pleasant nonsocial contrast. The scatterplots demonstrate the association between loneliness and activity in

this cluster in response to pleasant social pictures [r(21) = _.46, p < .05], and in response to pleasant nonsocial pictures [r(21) = .69, p < .001]. Estimated impulse

response functions and mean percent signal change AUC for participants lower and higher in loneliness (estimates at 1 SD above and below the mean UCLA score in

our sample are presented) show a crossover interaction for the relationship between loneliness and brain responses to pleasant social and pleasant nonsocial stimuli,

such that nonlonely participants exhibit greater activation to pleasant pictures that contain social content and lonely participants exhibit greater activation to pleasant

nonsocial pictures. (From Ref. [78])

Review Trends in Cognitive Sciences Vol.13 No.10

reversal learning associated with isolation in animals havealso been associated with diminished prefrontal-cortico-striatal functioning (a neural mechanism involved in theinhibition of previously learned responses) [21]. Sociallyisolated animals also show less dendritic arborization in

the hippocampus and prefrontal cortex [22] and decreasedbrain-derived neurotrophic factor [23]. To what extent lone-linessproduces similarneurophysiological changesandhowsuch differences contribute to cognitive decline in humansare open questions. Consistent with the animal research,

449

Review Trends in Cognitive Sciences Vol.13 No.10

however, human studies indicate that loneliness impairsexecutive functioning, specifically the inhibition of prepo-tent responses. We turn to that evidence next.

Executive functioningExecutive functioning includes the capacity to control one’sattention, cognition, emotion and/or behavior to bettermeet social standards or personal goals, that is, to self-regulate. Early evidence from young adults who performeda dichotic listening task suggested that attentional regu-lation was poorer in lonely than nonlonely individuals [24].Participants were asked to identify the consonant-vowelpair presented in the left or right ear. Typically, perform-ance shows a right-ear advantage and performance isbetter for the ear to which participants have beeninstructed to attend. Lonely and nonlonely individualsshowed an equivalent right-ear advantage under the no-instruction condition and an equivalent attentional shift tothe right ear when so instructed, but lonely participantsshowed a weaker left-ear advantage (the non-prepotentresponse) when instructed to attend to this ear.

Poorer self-regulation when feeling isolated is not lim-ited to attentional control. In cross-sectional and longitudi-nal research, lonely individuals have been found to have alower probability of engaging in regular exercise thannonlonely individuals, and the poorer emotional regulationof individuals when they felt lonely mediated the effect[25]. Experimental manipulations that lead people tobelieve they face a future of social isolation also decreaseself-regulation. In an illustrative study, Baumeister andcolleagues [26] had the participants complete two ques-tionnaires: an introversion/extraversion test and a person-ality inventory. Participants were then randomly assignedto receive no feedback (Control Group) or to receive feed-back to induce feelings of a future of social isolation (FutureAlone), social connection (Future Belonging) or generalmisfortune (Misfortune Control Group). Results revealedthat the Future Alone group performed significantly worsethan the other groups on theGeneralMental Ability Test ofthe Graduate Record Exam. Feedback of misfortune itselfwas insufficient to cause poor performance whereas badnews about social connections did.

In subsequent variations on this experimental para-digm, randomly assigned participants to the Future AloneGroup, relative to the other groups, performed similarly ona rote memorization task. However, they attempted thefewest problems and made the most mistakes on a logicalreasoning task [27], consumed more delicious butunhealthy foods [27] and were more aggressive towardothers [28]. Therefore, a perceived future of social isolationdid not impair routine mental ability, but did impair thehigher order cognitive and self-regulatory processes thatare characteristic of executive functioning. A brain scanconducted while participants performed moderately diffi-cult math problems revealed that the brains of the futuresocially isolated participants were less active in the areasinvolved in the ‘executive control’ of attention [29].

Colorations of cognitionExperimental manipulations of loneliness not only impairexecutive functioning but also produce higher negative

450

mood, anxiety, anger and depressive symptomatology[30]. An experience sampling study, in which participantswere beeped randomly nine times per day for seven days,confirmed that the social interactions of lonely, in contrastto nonlonely, individuals were more negative and lesssatisfying and such interactions contributed subsequentlyto more negative moods and interactions [31]. Evidencefrom behavioral and functional magnetic resonance ima-ging (fMRI) studies further suggests that lonelinessincreases attention to negative social stimuli (e.g. socialthreats). Using a modified emotional Stroop task, lonelyparticipants, relative to nonlonely participants, showedgreater Stroop interference specifically for negative socialrelative to negative nonsocial words [32]. No differencesbetween lonely and nonlonely participants were found inStroop interference for positive-social words relative topositive non-social words. Stroop interference is used togauge the implicit processing of stimuli and so theseresults suggest that loneliness is associated with a heigh-tened accessibility of negative social information. Sim-ilarly, Yamada and Decety [33] investigated the effectsof subliminal priming on the detection of painful facialexpressions. Using signal detection analyses, they foundthat lonely individuals were more sensitive (d0) to thepresence of pain in dislikable faces than were nonlonelyindividuals.

The patterns of regional brain activation found whenlonely and nonlonely individuals think about people alsodiffer [34]. A region associated with reward and appetitivebehavior (i.e. ventral striatum) was more strongly acti-vated in nonlonely than lonely individuals when exposed topleasant social pictures in contrast to pleasant nonsocialpictures (Figure II). By contrast, activation of the visualcortex to the presentation of unpleasant social, in contrastto nonsocial, pictures was directly related to the lonelinessof the participant, indicative of greater visual attention tothe negative social stimuli. These results are consistentwith the behavioral data and indicate that loneliness isrelated to the attention elicited by negative social stimuli.

A possible effect of loneliness and the priming of socialthreats is an increased probability that lonely individualsfocus on themselves, their needs and their preservation innegative circumstances. To examine this possibility, acti-vation in the temporoparietal junction (TPJ), a region thathas been found previously to be activated in theory of mindtasks and in tasks in which individuals take the perspect-ive of another, was also examined [34]. Consistent with thisreasoning, TPJ activation was observed when participantsviewed unpleasant pictures of people versus objects, andloneliness was inversely related to the amount of acti-vation observed.

The hypersensitivity to negative social information andthe diminished pleasure derived frompositive social stimulimight be expected to shape social expectations and motiv-ations and contribute to a downward spiraling of negativeaffect and depressive symptomatology. Indeed, loneliness isrelated to stronger expectations of, andmotivations toavoid,bad social outcomes and weaker expectations of, andmotiv-ations to approach, good social outcomes [35]. Furthermore,loneliness and depressive symptoms are distinct states bothby measures of statistical [30] and functional independence

Box 3. Regulatory loop and remaining questions

Given our evolutionary heritage, the human brain and biology have

been sculpted to seek meaningful connections with others. In evolu-

tionary time, social groupings were relatively small and stable, and the

pain of loneliness may have served both to promote the social

connections necessary for the survival of the genes and as a deterrent

to selfish actions that were detrimental to the group [58]. The evidence

reviewed here, however, suggests that loneliness in contemporary

society may sometimes affect human cognition in maladaptive ways

(Figure III). Specifically, feeling socially isolated can trigger implicit

hypervigilance for social threats, which in turn produces attentional,

confirmatory and memorial biases. Accordingly, lonely individuals are

more likely to attend to and construe their social world as threatening,

hold more negative social expectations and remember more negative

social events than are nonlonely individuals. These cognitions increase

the likelihood that individuals engage in behavioral confirmation

processes, through which they produce more negative social interac-

tions and elicit evidence confirming that they have little personal

control or social value. These dispositions, in turn, alter the nature and

likelihood of social engagement and activate neurobiological mechan-

isms that increase activation of the hypothalamic pituitary adrenal

(HPA) axis and diminish sleep quality. Repeated or chronic activation of

threat surveillance in a social context, coupled with diminished

anabolic processes, may contribute to heightened cognitive load,

diminished executive functioning, dysregulated brain and physiologi-

cal systems, and broad based morbidity and mortality. Although this

theoretical model is consistent with the evidence reviewed here, many

details remain to be tested and refined. The following questions may be

of special import.

� To what extent is loneliness a consequence rather than an

antecedent of incipient dementia? Longitudinal and experimental

studies suggest loneliness may play a causal role in at least some of

the observed associations between loneliness and cognitive

functioning, but sensory loss, functional impairments, and cogni-

tive impairments may also lessen social contact and increase

loneliness. Questions remain about the extent to which, and

conditions under which, the associations between loneliness and

cognitive functioning reflect the effects of loneliness, the effects of

cognition and the effects of a third variable.

� By what mechanism might loneliness contribute to cognitive

decline as people age? Among the possible mechanistic pathways

that warrant investigation are the effects of loneliness on: (a)

elevated activation of the HPA axis and/or increased inflammatory

responses in the brain, each of which may impact cognitive

functioning; (b) behavioral or neural plasticity such that older

individuals are less able to compensate for age-related degenera-

tive changes in neural systems involved in cognitive functioning; (c)

the simplification of social cognition and reduction in social

stimulation and engagement that are tantamount to lower cognitive

stimulation; (d) cognitive load (and reduction in available cognitive

resources available for creative adaptations) produced by chronic

surveillance for and protection from threats; (e) elevations in

depression and/or reductions in physical activity; (f) the reduction

in the number and quality of social interactions; and (g) impair-

ments in the consolidation of learning that may result from

diminished sleep quality.

� Does the detrimental effect of loneliness occur later in life or is it

cumulative across the lifespan? If cumulative, are the deleterious

effects of loneliness on cognition (if causal) reversible? Increasing

social contact and social support appear not to be sufficient to

lower loneliness or to explain the effects of loneliness on cognition.

How does one intervene to reduce perceived social isolation and

promote healthy social connections? Does the nature of effective

interventions for loneliness differ across age, gender, or ethnicity?

� What are the brain mechanisms underlying the association

between loneliness and cognition? Diminished prefrontal-cortico-

striatal functioning, dendritic arborization, brain-derived neuro-

trophic factors and central anti-inflammatory responses are just a

few of the possibilities that are suggested by the extant evidence.

Figure III. The effects of loneliness on human cognition.

Review Trends in Cognitive Sciences Vol.13 No.10

[36–38] and longitudinal studies have shown that lonelinesspredicts increases in depressive symptomatology in excessof what can be explained by basal levels of depressivesymptomatology [39–41]. Results are mixed in terms ofwhether depressive symptoms have a reciprocal influenceon loneliness.

Social cognitionThe brains of lonely, in contrast to nonlonely, individualsare on high alert for social threats, so lonely individualstend to view their social world as threatening and punitive(Box 3). Experimental manipulations of loneliness not onlycause people to feel more anxious, fear negative evaluation

451

Review Trends in Cognitive Sciences Vol.13 No.10

and act more coldly toward others [30], but it also causesthem to feel as assessed by ratings of room temperature[42]. Lonely individuals also tend to form more negativesocial impressions of others, and their expectations, attri-butional reasoning and actions toward others tend to beless charitable than shown by nonlonely individuals [43].When an individual’s negative social expectations elicitbehaviors from others that validate these expectations, theexpectations are buttressed and increase the likelihood ofthe individual behaving in ways that pushes away the verypeople to whom he or she most wants to be close to betterfulfill their social needs [44,45]. Consequently, lonely indi-viduals may view themselves to be passive victims in theirsocial world, but they are active contributors through theirself-protective and paradoxically self-defeating inter-actions with others [43].

Although loneliness can interfere with a person’sattempts to form stable and trusting social connectionswith other people, loneliness has been found to promoteattempts to form social connections though memorial orinferentialmeans, such as through nostalgic reminiscences[46], imputed parasocial relationships (relationships withimaginary television characters) [47] and digital connec-tions [48]. In addition, loneliness promotes social connec-tion through the anthropomorphism of pets [49],technological gadgets [50], celestial bodies [51], and super-natural entities [51]. This body of work suggests that whenpeople feel socially isolated it becomes more probable thatthey will use their cognitive capacities to try to fill thesocial void.

ContagionLoneliness is typically investigated as an individual factor,but because perceived and objective isolation can be differ-entiated, loneliness can also varywithin and across groups.Network linkage data from the population-based Framing-ham Heart Study were used to trace the topography ofloneliness in social networks and the path through whichloneliness spreads through these networks [52]. Resultsindicated that loneliness occurs in clusters within socialnetworks, is disproportionately represented at the periph-ery of social networks, extends up to three degrees ofseparation and is stronger for women than men.

Several features of the Framingham study pointed toloneliness spreading through a contagious process andmoving lonely individuals closer to the edge of social net-works over time. Contagion is defined as the transmissionof a state by direct or indirect contact, and virulence isdetermined, in part, by exposure (i.e. dose). Longitudinalanalyses indicated four findings. First, that loneliness inone individual at Time 1 was followed by increased lone-liness in others in the social network by Time 2. Second, thecloser a friend or contact was physically to this individualat Time 1, the lonelier the friend or contact became by Time2. Third, loneliness was transmitted from the individual atTime 1 through friends and contacts to others beyond theindividual’s circle of contacts such that these other indi-viduals became lonelier by Time 2. Fourth, the trans-mission of loneliness was stronger when the friendshipbetween the individual who was lonely at Time 1 andothers in the social network was reciprocal. Importantly,

452

these results were unchanged when controlling fordepressive symptomatology, indicating that the contagionof loneliness was not secondary to depression [52].

If loneliness is contagious, the driving away of thosewhoare lonely functions to keep the contagion in check with theconsequence that those who feel socially isolated becomeobjectively more isolated. Loneliness not only spreads fromperson to person within a social network, but it alsoreduces the ties of these individuals to others within thenetwork. The collective rejection of isolates observed inhuman and other primate behavior may therefore serve toprotect the structural integrity of the social entities necess-ary for humans to survive and prosper.

Data from the Framingham study do not permitdetailed investigation of the means by which lonelinesswas transmitted, but this contagion may occur throughthree different mechanisms: automatic emotional conta-gion [53], coextensive self–other overlap and the attendantsusceptibility of shared states [54], and quality of socialinteractions [31]. For instance, in an experience samplingstudy of everyday behavior, loneliness was associated withmore negative affect andmore negative social interactions,the quality of social interactions predicted subsequentaffective states and vice versa, and more negative socialinteractions had longer lasting effects on affect thanpositive social interactions [31]. These data are consistentwith the notion that the contagion of loneliness can occurthrough the more negative social cognition and interper-sonal interactions it engenders.

ConclusionCognition has been regarded as a quintessential individualactivity. Mental representations and processes were ren-dered testable in the dawnof the cognitive sciences by virtueof reverse engineering: mathematical and computer modelswere created that specified stimulus inputs, informationprocessing operations that acted on and transformed theseinputs to produce and change representational structures,and information processing operations that led to observa-ble responses. Computers today are no longer solitarydevices, but rather they operate as a connected collectiveresulting in unforeseen power, capacities, representationsand processes. Social species create emergent organizationsbeyond the individual – structures ranging from dyads andfamilies to institutions and cultures. These emergent struc-tures evolved hand in hand with neural, hormonal andgenetic mechanisms to support them because the conse-quent social behaviors helped these organisms survive, re-produce and care for offspring over a sufficiently long periodso that they too reproduced. These emergent levels of organ-ization have long been apparent, but identifying their bio-logical and cognitive bases and consequences is one of themajor problems for the cognitive sciences to address thiscentury.

Disclosure statementThis research was supported by the National Institute ofAging Program Project Grant No. PO1 AG18911 & RO1AG034052-01 and by a grant from the John TempletonFoundation. These funding sources had no role or influencein the preparation of this review.

Review Trends in Cognitive Sciences Vol.13 No.10

References1 Ruan, H. and Wu, C.F. (2008) Social interaction-mediated lifespan

extension of Drosophila Cu/Zn superoxide dismutase mutants. Proc.Natl. Acad. Sci. U. S. A. 105, 7506–7510

2 Nonogaki, K. et al. (2007) Social isolation affects the developmentof obesity and type 2 diabetes in mice. Endocrinology 148, 4658–

46663 Karelina, D. et al. (2009) Social isolation alters neuroinflammatory

response to stroke. P. Natl. A. Sci. 106, 5895–59004 Dronjak, S. et al. (2004) Immobilization and cold stress affect

sympatho-adrenomedullary system and pituitary-adrenocortical axisof rats exposed to long-term isolation and crowding. Physiol. Behav. 81,409–415

5 Stranahan, A.M. et al. (2006) Social isolation delays the positive effectsof running on adult neurogenesis. Nat. Neurosci. 9, 526–533

6 Kanitz, E. et al. (2004) Consequences of repeated early isolation indomestic piglets (Sus scrofa) on their behavioural, neuroendocrine, andimmunological responses. Brain Behav. Immun. 18, 35–45

7 Nation, D.A. et al. (2008) The effect of social environment onmarkers ofvascular oxidative stress and inflammation in the Watanabe heritablehyperlipidemic rabbit. Psychosom. Med. 70, 269–275

8 Poletto, R. et al. (2006) Effects of early weaning and social isolation onthe expression of glucocorticoid and mineralocorticoid receptor and11beta-hydroxysteroid dehydrogenase 1 and 2 mRNAs in the frontalcortex and hippocampus of piglets. Brain Res. 1067, 36–42

9 Weiss, R.S. (1973) Loneliness: The Experience of Emotional and SocialIsolation. MIT Press

10 Cacioppo, J.T. and Patrick, B. (2008) Loneliness: Human Nature andThe Need for Social Connection. W. W. Norton & Company

11 Herrmann, E. et al. (2007) Humans have evolved specialized skills ofsocial cognition: the cultural intelligence hypothesis. Science 317,1360–1366

12 Dunbar, R.I.M. and Shultz, S. (2007) Evolution in the social brain.Science 317, 1344–1347

13 Silk, J.B. et al. (2003) Social bonds of female baboons enhance infantsurvival. Science 302, 1231–1234

14 Schrijver, N.C. et al. (2004) Double dissociation of social andenvironmental stimulation on spatial learning and reversal learningin rats. Behav. Brain Res. 152, 307–314

15 Tilvis, R.S. et al. (2004) Predictors of cognitive decline and mortality ofaged people over a 10-year period. J. Gerontol. A. Biol. Sci. Med. Sci. 59,M268–M274

16 Wilson, R.S. et al. (2007) Loneliness and risk of Alzheimer disease.Arch. Gen. Psychiatry 64, 234–240

17 Gow, A.J. et al. (2007) Social support and successful aging:Investigating the relationships between lifetime cognitive changeand life satisfaction. J. Indiv. Differ. 28, 103–115

18 Bartels, M. et al. (2008) Genetic and environmental contributions tostability in loneliness throughout childhood. Am. J. Med. Genet. B.Neuropsychiatr. Genet. 147, 385–391

19 Boomsma, D.I. et al. (2005) Genetic and environmental contributions toloneliness in adults: The Netherlands twin register study. Behav.Genet. 35, 745–752

20 Hertzog, C. et al. (2008) Enrichment effects on adult cognitivedevelopment: can the functional capacity of older adults bepreserved and enhanced? Psychological Science in the Public Interest9, 1–65

21 Heidbreder, C.A. et al. (2000) Behavioral, neurochemical andendocrinological characterization of the early social isolationsyndrome. Neuroscience 100, 749–768

22 Silva-Gomez, A.B. et al. (2003) Decreased dendritic spine density onprefrontal cortical and hippocampal pyramidal neurons inpostweaning social isolation rats. Brain Res. 983, 128–136

23 Barrientos, R.M. et al. (2003) Brain-derived neurotrophic factor mRNAdownregulation produced by social isolation is blocked byintrahippocampal interleukin-1 receptor antagonist. Neuroscience121, 847–853

24 Cacioppo, J.T. et al. (2000) Lonely traits and concomitant physiologicalprocesses: the MacArthur social neuroscience studies. Int. J.Psychophysiol. 35, 143–154

25 Hawkley, L.C. et al. (2009) Loneliness predicts reduced physicalactivity: cross-sectional and longitudinal analyses. Health Psychol.28, 354–363

26 Baumeister, R. and DeWall, N. (2005) The inner dimension of socialexclusion: Intelligent thought and self-regulation among rejectedpersons. In The Social Outcast: Ostracism, Social Exclusion,Rejection, and Bullying (Williams, K.D. et al., eds), pp. 53–76,Psychology Press

27 Baumeister, R.F. et al. (2005) Social exclusion impairs self-regulation.J. Pers. Soc. Psychol. 88, 589–604

28 Twenge, J.M. et al. (2001) If you can’t join them, beat them: Effects ofsocial exclusion on aggressive behavior. J. Pers. Soc. Psychol. 81, 1058–

106929 Campbell, W.K. et al. (2006) A magnetoencephalography investigation

of neural correlates for social exclusion and self-control. Soc. Neurosci.1, 124–134

30 Cacioppo, J.T. et al. (2006) Loneliness within a nomological net: Anevolutionary perspective. J. Res. Pers. 40, 1054–1085

31 Hawkley, L.C. et al. (2007) Multilevel modeling of social interactionsand mood in lonely and socially connected individuals: The MacArthursocial neuroscience studies. InOxford Handbook of Methods in PositivePsychology (Ong, A.D. and van Dulmen, M., eds), pp. 559–575, OxfordUniversity Press

32 Shintel, H. et al. (2006) Accentuate the negative, eliminate thepositive? Individual differences in attentional bias to positive andnegative information. In 47th Annual Meeting of the PsychonomicSociety,

33 Yamada,M. andDecety, J. (2009) Unconscious affective processing andempathy: an investigation of subliminal priming on the detection ofpainful facial expressions. Pain 143, 71–75

34 Cacioppo, J.T. et al. (2008) In the eye of the beholder: individualdifferences in perceived social isolation predict regional brainactivation to social stimuli. J. Cogn. Neurosci. 21, 83–92

35 Gable, S.L. (2006) Approach and avoidance social motives and goals. J.Pers. 74, 175–222

36 Adam, E.K. et al. (2006) Day-to-day dynamics of experience—cortisolassociations in a population-based sample of older adults. P. Natl. A.Sci. U. S. A. 103, 17058–17063

37 Cole, S.W. et al. (2007) Social regulation of gene expression in humanleukocytes. Genome Biology 8, R189.181–R189.113

38 Hawkley, L.C. et al. (2006) Loneliness is a unique predictor of age-related differences in systolic blood pressure. Psychol. Aging 21, 152–

16439 Cacioppo, J.T. et al. (2006) Loneliness as a specific risk factor for

depressive symptoms: cross-sectional and longitudinal analyses.Psychol. Aging 21, 140–151

40 Heikkinen, R-L. and Kauppinen, M. (2004) Depressive symptoms inlate life: a 10-year follow-up. Arch. Gerontol. Geriatr. 38, 239–250

41 Wei, M. et al. (2005) Adult attachment, social self-efficacy,self-disclosure, loneliness, and subsequent depression for freshmancollege students: a longitudinal study. J. Couns. Psychol. 52, 602–

61442 Zhong, C.B. and Leonardelli, G.J. (2008) Cold and lonely: does social

exclusion literally feel cold? Psychol. Sci. 19, 838–84243 Cacioppo, J.T. and Hawkley, L.C. (2005) People thinking about people:

The vicious cycle of being a social outcast in one’s own mind. In TheSocial Outcast: Ostracism, Social Exclusion, Rejection, and Bullying(Williams, K.D. et al., eds), pp. 91–108, Psychology Press

44 Murray, S.L. et al. (2003) Once hurt, twice hurtful: How perceivedregard regulates daily marital interactions. J. Pers. Soc. Psychol. 84,126–147

45 Downey, G.D. and Romero-Canyas, R. (2005) Rejection sensitivity as apredictor of affective and behavioral responses to interpersonalstress: A defensive motivational system. In The Social Outcast:Ostracism, Social Exclusion, Rejection, and Bullying (Williams, K.D.et al., eds), The Psychology Press

46 Zhou, X. et al. (2008) Counteracting loneliness: on the restorativefunction of nostalgia. Psychol. Sci. 19, 1023–1029

47 Gardner,W.L. andKnowles, M.L. (2008) Lovemakes you real: Favoritetelevision characters are perceived as ‘‘real’’ in a social facilitationparadigm. Soc. Cognition 26, 156–168

48 Ozcan, N.K. and Buzlu, S. (2007) Internet use and its relation with thepsychosocial situation for a sample of university students.Cyberpsychol. Behav. 10, 767–772

49 Epley, N. et al. (2008) When we need a human: Motivationaldeterminants of anthropomorphism. Soc. Cognition 26, 143–155

453

Review Trends in Cognitive Sciences Vol.13 No.10

50 Epley, N. et al. (2008) Creating social connection through inferentialreproduction - Loneliness and perceived agency in gadgets, gods, andgreyhounds. Psychol. Sci. 19, 114–120

51 Epley, N. et al. (2007) On seeing human: a three-factor theory ofanthropomorphism. Psychol. Rev. 114, 864–886

52 Cacioppo, J.T. et al. (2009) Alone in the crowd: the structure and spreadof loneliness in a large social network. J. Pers. Soc. Psychol. 96

53 Hatfield, E. et al. (1994) Emotional Contagion. Cambridge UniversityPress

54 Slotter, E.B. and Gardner, W.L. (2009) Where do you end and I begin?Evidence for anticipatory, motivated self-other integration betweenrelationship partners. J. Pers. Soc. Psychol. 96, 1137–1151

55 Hawkley, L.C. et al. (2008) From social structure factors to perceptionsof relationship quality and loneliness: The Chicago Health, Aging, andSocial Relations Study. J. Gerontol. B. Psychol. 63, S375–S384

56 Ruiz, J.I. (2007) Emotional Climate in Organizations: applications inlatin american prisons. J. Soc. Issues 63, 289–306

57 Boomsma, D. et al. (2005) Genetic and environmental contributions toloneliness in adults: The Netherlands Twin Register Study. Behav.Genet. 35, 745–752

58 Cacioppo, J.T. and Patrick, B. (2008) Loneliness: Human Nature andthe Need for Social Connection. W. W. Norton & Company

59 Dykstra, P.A. and Fokkema, T. (2007) Social and emotional lonelinessamong divorced and married men and women: comparing the deficitand cognitive perspectives. Basic. Appl. Soc. Psych. 29, 1–12

60 Cacioppo, J.T. andHawkley, L.C. (In press) Loneliness. InHandbook ofIndividual Differences in Social Behavior (Leary, M.R. andHoyle, R.H.,eds), Guilford

61 Hawkey, L.C. et al. (2006) Loneliness is a unique predictor of age-relateddifferences in systolic blood pressure. Psychol. Aging 21, 152–164

62 Hawkley, L.C. et al. (2009) Loneliness predicts reduced physicalactivity: cross-sectional & longitudinal analyses. Health Psychol. 28,354–363

63 Wen, M. et al. (2006) Objective and perceived neighborhoodenvironment, individual SES and psychosocial factors, and self-rated health: an analysis of older adults in Cook County. Illinois.Soc. Sci. Med. 63, 2575–2590

454

64 Baumeister, R.F. et al. (2002) Effects of social exclusion on cognitiveprocesses: Anticipated aloneness reduces intelligent thought. J. Pers.Soc. Psychol. 83, 817–827

65 Cole, S.W. (2008) Social regulation of leukocyte homeostasis: the role ofglucocorticoid sensitivity. Brain Behav. Immun. 22, 1049–1055

66 Adam, E.K. et al. (2006) Day-to-day dynamics of experience-cortisolassociations in a population-based sample of older adults. Proc. Natl.Acad. Sci. U. S. A. 103, 17058–17063

67 Steptoe, A. et al. (2004) Loneliness and neuroendocrine,cardiovascular, and inflammatory stress responses in middle-agedmen and women. Psychoneuroendocrinology 29, 593–611

68 Eisenberger, N.I. et al. (2003) Does Rejection Hurt? An fMRI Study ofSocial Exclusion. Science 302, 290–292

69 Delgado, M.R. et al. (2005) An fMRI study of reward-related probabilitylearning. Neuroimage 24, 862–873

70 O’Doherty, J.P. (2004) Reward representations and reward-relatedlearning in the human brain: insights from neuroimaging. Curr.Opin. Neurobiol. 14, 769–776

71 Leyton, M. (2007) Conditioned and sensitized responses to stimulantdrugs in humans. Prog. Neuropsychopharmacol. Biol. Psychiatry 31,1601–1613

72 Wang, Z. et al. (2007) Neural substrates of abstinence-inducedcigarette cravings in chronic smokers. J. Neurosci. 27, 14035–14040

73 Seymour, B. et al. (2007) Differential encoding of losses and gains in thehuman striatum. J. Neurosci. 27, 4826–4831

74 Aron, A. et al. (2005) Reward, motivation, and emotion systemsassociated with early-stage intense romantic love. J. Neurophysiol.94, 327–337

75 Rilling, J. et al. (2002) ANeural basis for social cooperation.Neuron 35,395–504

76 Fliessbach, K. et al. (2007) Social comparison affects reward-relatedbrain activity in the human ventral striatum. Science 318, 1305–1308

77 De Quervain, D.J.F. et al. (2004) The neural basis of altruisticpunishment. Science 305, 1254–1258

78 Cacioppo, J.T. et al. (2009) In the eye of the beholder: individualdifferences in perceived social isolation predict regional brainactivation to social stimuli. J. Cogn. Neurosci. 21, 1–10