Motivation and emotion/Book/2017/Loneliness

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What is loneliness, what does it matter, and how can it be managed?

Overview[edit | edit source]

Have you ever felt alone in a crowd of people? Do you feel sad and distressed when you're separated from others? Have you lost a loved one and feel like you have nothing left? You are not alone. Feelings of loneliness are a common experience with many individuals reporting a bout in their lifetime with some reporting transient to chronic states.

In this chapter, what loneliness is, how loneliness manifests, how it affects our lives is examined. A plethora of antecedents and consequences [vague] are considered across the lifespan. [which?] Theories and models are examined in relation to loneliness development across the lifespan.

Figure 1. Depiction of lonely behaviour on Schiermonnikoog island.

Loneliness[edit | edit source]

Loneliness, a complex and intense emotion, is a common experience. It is related to social connectedness, communication and peer influences (Perlman & Peplau, 1981). Lack of these influences result in feelings of loneliness and isolation. It has multiple antecedents but is often associated with negative affect (Bauminger & Kasari, 2000). Loneliness can be seen as the subjective counterpart to the objective measure of social isolation or as the antithesis to social support (Andersson, 1998).

The definition of loneliness varies amongst the literature with many discounting societal influences, personal values and later on, consequences. Wenger (1984) refers to loneliness as the perceived deprivation of social contact. Rook (1984) states that it is the result of the lack of people willing to share socio-emotional experiences. Shalev (1988) notes that it is a state where individuals have the ability to socialise but refuse to do so. Others state that loneliness is the notable discrepancy between desired and realistic interactions (Reichmann, 1959). In part, all these definitions are appropriate but only reflect small parts of a larger construct. De Jong Gierveld (1989), adopting a cognitive approach, provides the following empirically supported definition of loneliness which adequately sums the aforementioned definitions:

"Loneliness is a situation experienced by an individual as one where there is an unpleasant or inadmissible lack of (and quality of) certain relationships. This includes situations in which the number of existing relationships is smaller than is considered desirable or admissible, as well as situations where the intimacy one wishes for has not been realised. Thus, loneliness is seen to involve the manner in which the person perceives, experiences, and evaluates his or her isolation and lack of communication with other people". (de Jong Gierveld, 1989).

It is estimated that 20% of the global population at any one time are experiencing feelings of loneliness (Peplau & Perlman, 1982). As such, loneliness does not discriminate. Individuals in relationships, those with families, in a strong marriage, or with a large circle of friendships can experience bouts of loneliness. Cross-cultural studies maintain that loneliness is mostly indiscriminate. (Andrews, 2017).

Types of loneliness[edit | edit source]

Although the above definition is rather broad, loneliness is multidimensional (Perlman & Peplau, 1981). No two people experience loneliness the same way, rather, they each experience a different form of loneliness contingent on personal antecedents (Weiss, 1982). Thus, loneliness is a subjective experience.

  • Emotional loneliness, an acutely painful form of isolation, is due to the lack of affective and fulfilling bonding with other people (Perlman & Peplau, 1981). Resulting in restlessness and deepened levels of sadness, it is often synonymous with depression. Earlier writings by Moustakas (1961) referred to emotional loneliness as "loneliness anxiety", an aversive response to alienation between humankind.
  • Social-cognitive loneliness is rooted in cognitive processes such as self-evaluation, self-perception and social comparison (Bauminger & Kasari, 2000). This form of loneliness, also referred to as existential loneliness, is an "inevitable part of the human experience" providing a path for triumphant self-creation (Moustakas, 1961).
  • Social loneliness refers to the lack of social connectedness and a sense of belonging (Weiss, 1982). Experienced as an amalgamation of rejection and nonacceptance, ennui and exclusion has been reported in some individuals (Bauminger & Kasari, 2000).

Loneliness, in transient temporary states, may prove valuable in terms of developing a stronger sense of self{. As a chronic trait, it is detrimental to health, the self and interpersonal relationships.

Affective manifestations and antecedents[edit | edit source]

Figure 2. "Why can't we talk, at least?". Up to 90% of lonely individuals admit they haven't told anyone they are lonely.

Loneliness is an extremely unpleasant experience. Loneliness doesn't have a "look", it is a subjective emotional experience with each individual presenting differently. As such, to quote, "you can be lonely in a crowd, and you can be happy alone, but as a rule, it would be expected that people are more likely to feel lonely when they are by themselves", thus manifestations are specific to the individual (Shalev, 1988). Reichmann (1959) writes of it as a "painful and frightening" occurrence often associated with bouts of depression. Common affective manifestations of loneliness include dissatisfaction, emptiness, restlessness, a lack of assertiveness, anxiety and boredom (Moustakas, 1961; Weiss, 1982). A progressive association has also been established between loneliness and hostility, particularly in interpersonal relationships (Loucks, 1974)[explain?]. Similarly, a negative outlook, reduced happiness and satisfaction from activities and relationships and increased pessimism have been consistent findings (Loucks, 1974). Some lonely individuals are also helpless in the resolution of their condition, often accepting their social deprivations. These social deprivations are seen as unavoidable with lonely individuals being indifferent to social stimuli (de Jong-Gierveld, 1989).

Identifying specific antecedents for loneliness is a complex task. Often, causes of loneliness are situational - those that involve a disruption to the quality of relationships with others. Loss in a general sense is the most common cause of loneliness, whether it be through bereavement, loss of a friend, or separation from a significant other (Shalev, 1988). Marital or divorce status, current social environment, inadequate social networks, transport availability, financial insecurity and social media dependency have also been found to contribute to the formation of loneliness (Shalev, 1988; Perlman & Peplau, 1981; Loucks, 1974). de Jong Gierveld (1989) notes that personal characteristics such age and gender have an association although not a strong one.

Other antecedents of loneliness include characterological factors. Some authors suggest that lonely individuals are selfish and do not think of others often (de Jong, 1989). In Louck's (1974) publication, he summarised that loneliness is negatively[say what?] related to concepts such as self-esteem, depression, shyness, anxiety, anger and tension, greater neuroticism, lower extroversion, higher self-consciousness, self-blame and devaluation, and lastly, lower education levels. Cause and effect is yet to be established, however, the aforementioned characterological factors are often concurrent with loneliness.

Who experiences Loneliness?

The Loneliness Survey released by Lifeline (2016) reports the following about lonely Australians:

  1. 8 in 10 Australians report high levels of loneliness with 60% of respondents claiming they "often felt lonely".
  2. 28% of participants called Lifeline during a bout of loneliness.
  3. The top three living arrangements of lonely Australians: ~22% lived with a spouse/partner and others, ~22% lived only with a spouse/partner, and ~20% lived alone.
  4. 34% of participants did not have someone to confide in when feelings of loneliness arose.
  5. 83% agree with the notion that loneliness is increasing in our society.
  6. A 7% increase in calls during holidays due to the "summer time blues epidemic".
  7. For elderly individuals, television is the main form of "company", with many not having any form of communication with friends and family for over a month.
  8. 9 in 10 lonely individuals are afraid to admit they are lonely, thus, continue to suffer in silence (Andrews, 2017).

Refugees and migrants (58%), parents (24%) and those with disability (50%) report the greatest levels of loneliness on any given day (Andrews, 2017).

Activity: Self Quiz

1. Loneliness is:

Singular and easily definable.
Multifaceted and based on subjective experiences.
Based on individual perception.
The same as solitude, selective loneliness and social isolation.

Associated motivation theory[edit | edit source]

Two viewpoints concerning the motivational aspects of loneliness have been identified. Some authors state that loneliness is arousing (Sullivan, 2013), others state that loneliness decreases motivation (Reichmann,1959).

Arousal[edit | edit source]

Sullivan (2013) states that loneliness is a "driving force", motivating individuals to initiate social interaction. Cacioppo and Hawkley (2006) supported this notion. Their research states that the absence of fulfilling social interactions trigger similar primal responses such as those made when in physical pain; the motivation is for the pain to be removed. Specifically, the pain associated with loneliness and the reward associated with social connectedness motivates the individual to reduce loneliness and maintain social relationships (Andersson, 1998). Rilling and colleagues (2002) further note that an individual will maintain social relationships even when their self-interests are not met to reduce the associated social pain.

Inhibition[edit | edit source]

Reichmann (1959) disagrees with the motivational force of loneliness, suggesting instead that true loneliness creates a "paralysing hopelessness and unalterable futility". Weiss (1982) counters this notion, suggesting that tasks lose their importance. In surveys, lonely people respond highly on Likert-scales to items such as "at times I feel worn out for no reason" and "my strength often seems to drain away from me" (Perlman & Peplau, 1981). In another study, lonely respondents were found to lack "vigour", lively enthusiasm, and reported overall reduced energy (Loucks, 1974). Evidently, this lack of enthusiasm and vigour contrasts the hyperactivity associated with anxiety and arousal.

Lonely individuals report high self-consciousness, low levels of concentration and make more errors than non-lonely people on paired-association tasks (Perlman & Peplau, 1981). In some cases, "loneliness produces an oversensitivity to minimal cues and a tendency to misinterpret or to exaggerate the hostile or affectionate intent of others (Weiss, 1982).

The importance of loneliness[edit | edit source]

The general perception is that loneliness causes a rapid decrease in well-being. Longitudinal research corroborates this perception, noting that loneliness predicts increased morbidity and mortality (Hawkley & Cacioppo, 2013). Astonishingly, loneliness and its consequences cost the [which?] economy $54 billion a year (Andrews, 2017). Among latent causes of hospitalisation, loneliness is reported to one of the highest contributing factors (de Jong Gierveld, 1989).

Loneliness in childhood and adolescence[edit | edit source]

Figure 3. Max Pixel's depiction of Loneliness in a crowd.

Loneliness during childhood is an early indicator of future social and self-development deficits. Attachment theory states that a strong emotional and physical attachment to a caregiver is paramount to healthy development (Bowlby, 1958). As previously stated, lonely individuals avoid social situations where social engagement may occur. Anxious-ambivalent attachment is aversion to exploration and uneasiness in the presence of strangers (Crittenden, 1999). In young children, this leads to the avoidance of social situations where friends could be made (school, playgrounds, etc). Children with anxious-ambivalent attachment styles experience limited social interactions in new environments, have a reduced quality and quantity of relationships and tend to express greater levels of hopelessness or anger (Bowlby, 1958). Without the presence of a trusted caregiver, the chance of the child approaching situations is dramatically reduced and replaced with avoidant behaviour, and thus, decreased personal and social skill development. Similar to anxious-ambivalent attachment styles, anxious-avoidant attachment results in avoidance of novel situations regardless of caregiver presence (Crittenden, 1999). Children expressing this style of attachment often have little interest in contact-maintaining behaviour as they age and show limited motivation to appraise situations differently (Bowlby, 1958).

These attachment styles carry throughout the lifespan influencing the quantity and quality of future social interactions, social circles and the approaching of novel situations. Lonely adolescents, as a result of the maladaptive attachment styles, "grow into" these styles, continuing the cycle of avoidant behaviour and appraising some situations as unsafe. Both anxious-ambivalent and anxious-avoidant adolescents develop low self-esteem and decreased trust in others, further decreasing their chances to participate in novel social environments (Crittenden, 1999). Lonely adolescents also exhibit avoidant and sometimes anti-social behaviour in school environments, often rejecting opportunities to make friends, interact with teachers, participate in group activities that aid academic achievement and development of self[factual?].

Figure 4. Old Man in Sorrow. An interpretation of loneliness.

As noted by Erikson (1963) in his theory of psychosocial development, the developmental transition from childhood to adolescence is a time characterised by identity establishment, independence and autonomy through self exploration (Stage 5: identity vs. role confusion). During stage 5, adolescent individuals are at a stage of development "between the morality learned by the child and the ethics to be developed by the adult" (Erikson, 1963, p. 245). By way of goal, value and belief evaluation, the self develops, and if successful leads to the virtue of fidelity. Fidelity involves the ability to commit to the basis of accepting others even when ideological differences are present (Erikson, 1963). Failure of fidelity results in role confusion, a typical characteristic of lonely adolescents. Subversion, antisocial behaviour, emotional issues and heightened hostility arise due to role confusion. As such, lonely adolescents are more likely to participate in violent crime and maintain a criminal lifestyle. Associated lifestyle habits such as drugs and alcohol abuse has additionally been reported in lonely adolescents (Steptoe et al., 2013). In some cases, lonely adolescents report higher incidences of mental health comorbidity, specifically depression and schizoid personality disorder, compared to their non-lonely counterparts (Cacioppo et al., 2006).

Overall, due to loneliness, ennui, inhibition and avoidance behaviours result in a marked reduction in life skills, social skills, future employment opportunities and detrimental health consequences[Rewrite to improve clarity].

Loneliness in adulthood and old age[edit | edit source]

Recent research shows that loneliness is associated with a plethora of health and social issues. The loss of a close partner and deteriorating health are amongst the most salient determinants of loneliness development (de Jong Gierveld, 1989).

Most shockingly, loneliness increases the risk of premature death by three times (Cacioppo et al., 2006). Higher incidences of psychosomatic headaches, poor appetite, restlessness and decreased energy are additionally found in lonely individuals compared to non-lonely people (Shaver & Rubenstein, 1980). Functional impairments, cardiovascular disease, diminished immunosurveillance and premature death also maintain a higher prevalence in lonely individuals (Lynch, 2000).

In chronic loneliness sufferers, there is an increased risk of developing inflammatory diseases, reduced immune responses and rapid health deterioration (Cacioppo & Hawkley, 2015). High systolic blood pressure, HDL cholesterol and low oxygen consumption are also associated with middle-age adult loneliness in addition to a rapid loss of executive function (Hawley & Cacioppo, 2015; Steptoe et al., 2013). Additionally, while sleep offers restoration properties for the body, chronic loneliness suffers are often tormented by sleepless nights and low sleep quality. As such, sleep deprivation effects the cardiovascular functioning, metabolic issues, hypertension, coronary artery calcification and higher rates of inflammation (Hawkley & Caccioppo, 2013).

Figure 5. The ACE pyramid, typically used in childhood stress studies, can be useful at summarising the consequences of loneliness.

Pathological consequences of loneliness are typically found in lonely adults who have personality and behavioural disorders such as alcoholism, extreme anxiety, stress, and low self-esteem (de Jong Gierveld, 1989). Mental health issues such as depression, suicidal idealisation, anxiety, schizophrenia and paranoia are highly correlated with loneliness, with more lonely individuals than non-lonely individuals presenting with co-morbid mental health disorders (Cacioppo et al., 2006).

Specific to elderly sufferers, they are 3.4 times more likely to suffer from depression and 1.9 times more likely to develop a form of dementia in the following decade compared to their non-lonely counterparts (Andrews, 2017). Sadly, loneliness at age 79 predicts "lifetime cognitive change" and a decrease in IQ, symptoms associated with dementia. Lonely elders are also more likely to be physically inactive, leading to a 7% increase in diabetes development, 8% increase in stroke incidences and 14% increase in CHD conditions[factual?]. Lonely elderly individuals are 1.8 times more likely to attend the emergency department of hospitals, 1.3 times more likely to be admitted during said emergency visits, and 3.5 times more likely to enter public-funded residential care; all due to complications associated with loneliness (Andrews, 2017; Gransnet, 2017). Shockingly, due to the stigma associated with loneliness, 57% of elderly sufferers admit to never speaking to someone about their feelings, with a further 75% reporting family members and friends would be "astonished to hear that they feel lonely" (Gransnet, 2017).

Social Issues[edit | edit source]

The Loneliness Model posits that perceived isolation is similar to the feeling of being unsafe, thus, increases hypervigilance for social threat in environments (Hawkley & Cacioppo, 2013). Hypervigilance creates cognitive biases - the perception that the world is a lonely, threatening place. These biases held by lonely people lead to the misinterpretation of the intent of others, as previously noted by Weiss (1982), affecting an individuals social life. Interestingly, three characteristics of how lonely people interact and converse have been identified and relate to the Loneliness Model (Perlman & Peplau, 1981). First, lonely people tend to make fewer other-references and ask fewer questions of their partner. Secondly, they change the topic rapidly with greater frequency. Lastly, lonely people tend to extend pauses in conversations and are often unable to fill these gaps (Perlman & Peplau, 1981).

Figure 5 summarises the discussed problems associated with loneliness. Given the consequences of loneliness at any stage in the lifespan, it is no surprise that it is paramount to manage the condition. If left untreated, lonely individuals are more likely to commit suicide or participate in self-destructive behaviours that are life-threatening. Thus, management of the emotional condition is essential.

Australian Social Trends (ABS, 2009)
  1. The proportion of the population 15 years and over living alone increased from 9% to 12% in recent decades;
  2. In 2006, individuals aged 15+ years who lived alone spent an average of 61% of their waking hours alone. Lonely individuals over 65 years spend on average 74% of their waking hours alone.
  3. This [which?] statistics is projected to increase up to 16% in the next 20 years (accounting for approximately 3.1 million people);
  4. People who's[spelling?] partners passed away make up 68% of those who live alone (45% for men and 78% for women).
  5. Males between the ages of 25-44 years and single parent fathers are at the greatest risk of developing loneliness. 33% of males agree with the statementː "I often feel very lonely".
  6. 23% of women living alone report feelings of loneliness, with the highest levels reported by single parent mothers.

Management[edit | edit source]

Management of loneliness is extremely challenging. Management is contingent on emotional and social coping mechanisms rather than on medical approaches. In this sense, loneliness is treatable; not an irreversible condition (de Jong Gierveld, 1989). Perlman and Peplau (1981) suggest three solutions to managing loneliness:

Solution 1: Altering the desired levels of social contact can be achieved through three alternative methods: adaption, task choice, and changed standards.

  • Adaption is the process of changing personal standards that match and converge to an achievable level, thus appraising situations appropriately to conform to reality. Weiss (1982) agrees with this notion in principle, however, does not view it as an appropriate solution to loneliness.
  • Task choice refers to altering an individuals desired level of social contact by participating in tasks that can be enjoyed alone, such as reading. Creating feelings of enjoyment counteracts the effects of loneliness. Rubenstein and Shaver (1980) suggested that greater involvement in solitary activities is a useful way of reducing feelings of loneliness because a greater personal investment in a task is produced.
  • The changed standards approach suggests that changing standards of who is acceptable as a friend predicts recovery from bouts of loneliness. Perlman and Peplau (1981) provide the example: "consider a professional who usually forms friendships with other high status professionals: if this person became lonely, they might be willing, even happy, to form friendships with a much wider set of people" than professional associates.

Solution 2: Altering the realistic level of social contact - Perlman and Peplau (1981) suggest that the most effective method of managing and then overcoming loneliness is to improve social relationships and create new ones. In one of their surveys, they found that "finding a significant other" was perceived as the best way to overcome loneliness, followed by starting conversations with others, making the self physically appealing and joining clubs. The same survey found that students who had a larger social network exhibited fewer feelings of loneliness.

Solution 3: Altering the magnitude of the gap between desired and achieved levels of contact - Perlman and Peplau (1981) identified four themes in lonely individuals:

  1. lonely people often deny the evident discrepancy between desired and achieved social relations;
  2. lonely people 'devalue social contact' and rationalise this behaviour by saying that they have other things to do;
  3. lonely people present with reduced self-esteem and may compensate by engaging in non-prosocial behaviours, and lastly
  4. lonely people will often engage in behaviours associated with the alleviation of negative feelings i.e. drinking and use of drugs.

Addressing these four themes in an individual would aid management of loneliness and its negative affects.

Efforts to reduce and manage loneliness must be applied from multiple perspectives. As such, a large component of management and 'treatment' depends on the individual. The following suggestions have proven effective in past management plans for lonely people:

  1. Identifying lonely individuals and altering their perceptions (desired, actual, and the gap between the two) (Perlman & Peplau, 1981).
  2. Treating the root cause if there is one (such as mental health complications, stress, bereavement or divorce counselling) through ongoing therapy or personalised time management plans. Specifically, cognitive-behavioural therapy (CBT) has shown to effective at reducing loneliness by combating mental illness, cognitions and altering the appraisals given in situations (Cacioppo et al., 2015). In some cases, therapeutic interventions have proven effective and have highlighted the use of adjunctive pharmacological treatments as an additional aid (Cacioppo et al., 2015). In the long term, treatment of health conditions that may prevent an individual from seeking social connections is recommended.

Controversially, social media use as an aid to communicate with others has shown some promise in the short-term (Andrews, 2017). Although not ideal for long-term management due to the disconnected nature of such communications, maintaining some contact with others reduces feelings of perceived social isolation and loneliness. As indicated by Perlman and Peplau's (1981) research, these forms of communication change standards and equate to a form of adaption.

Given the complicated nature of loneliness, management begins at the individual level assessing and altering perceptions, appraisals and negative cognitions. The treatment of underlying medical and mental health issues is additionally paramount to reduce further decline in health, social isolation and chronic loneliness.

Conclusion[edit | edit source]

Loneliness is a complex emotion resulting in negative affect and devastating consequences if not managed. Three forms of loneliness have been established - emotional, social-cognitive and social loneliness. While many people suffer from loneliness, no two people experience the same feelings due to antecedents and active manifestations, thus, is a subjective experience. The implications of chronic loneliness are plentiful often resulting in rapidly declining health, isolation due to social skill deficits, increased hostility, and reduced approach behaviours. The management of loneliness begins at the individual level, assessing and changing current cognitions and appraisals of situations. Altering standards (desired, actual, and the gap between the two) is key to the successful management of loneliness, and in turn, dramatically reduces the burden loneliness places on an individual, their health and social lives.

See also[edit | edit source]

References[edit | edit source]

Andersson, L. (1998). Loneliness research and interventions: a review of the literature. Aging & Mental Health2(4), 264-274.

Andrews, S. (2017) The Silver Line: No Holiday from Loneliness. [Press release] Retrieved from

Bauminger, N., & Kasari, C. (2000). Loneliness and friendship in high‐functioning children with autism. Child development71(2), 447-456.

Bowlby, J. (1958) The nature of the child's tie to his mother. International Journal of Psychoanalysis. 39, 350-373

Cacioppo, J. T., Hughes, M. E., Waite, L. J., Hawkley, L. C., & Thisted, R. A. (2006). Loneliness as a specific risk factor for depressive symptoms: cross-sectional and longitudinal analyses. Psychology and aging21(1), 140.

Cacioppo, S., Grippo, A. J., London, S., Goossens, L., & Cacioppo, J. T. (2015). Loneliness: Clinical import and interventions. Perspectives on Psychological Science, 10(2), 238-249.

Crittenden, P. M. (1999). Danger and development: The organization of self-protective strategies. Monographs of the Society for Research in Child Development, 145-171.

de Jong-Gierveld, J. (1989). Personal relationships, social support, and loneliness. Journal of Social and Personal Relationships6(2), 197-221.

Eisenberger, N. I., Lieberman, M., & Williams, K. D. (2003). 'Does rejection hurt? An fMRI study of social exclusion. Science, 302, 290–292.

Erikson, E. H. (1963). Childhood and society (Rev. ed.). 159-256.

Gransnet (2017) Survey reveals over half of older people are silent about loneliness. [Press release] Retrieved from

Lifeline (2017) The Loneliness Survey. [Press release] Retrieved from

Loucks, S. (1974). The dimensions of loneliness: A psychological study of affect, self-concept, and object-relations (Doctoral dissertation, ProQuest Information & Learning).

Lynch, J. J. (2000). A cry unheard: New insights into the medical consequences of loneliness. Bancroft Press. Moustakas, C. E. (1961). Loneliness. New York: Prentice-Hall.

Perlman, D., & Peplau, L. A. (1981). Toward a social psychology of loneliness. Personal relationships3, 31-56.

Rook, K. S. (1987). Social support versus companionship: Effects on life stress, loneliness, and evaluations by others. Journal of Personality and Social Psychology, 52(6), 1132-1147.

Shalev, S. (1988). On loneliness and alienation. The Israel Journal of Psychiatry and Related Sciences, 25(4), 236-245.

Shaver, P., & Rubenstein, C. (1980). Childhood attachment experience and adult loneliness. Review of personality and social psychology1, 42-73.

Steptoe, A., Shankar, A., Demakakos, P., & Wardle, J. (2013). Social isolation, loneliness, and all-cause mortality in older men and women. Proceedings of the National Academy of Sciences', 110(15), 5797-5801.

Sullivan, H. S. (Ed.). (2013). The interpersonal theory of psychiatry. Routledge.

Walton, C. G., Shultz, C. M., Beck, C. M., & Walls, R. C. (1991). Psychological correlates of loneliness in the older adult. Archives of psychiatric nursing, 5(3), 165-170.

Weiss, R. S. (1982). Issues in the study of loneliness. Loneliness: A sourcebook of current theory, research and therapy, 71-80.

Reichmann, F. F. (1959). Loneliness. Psychiatry22(1), 1-15.

Rilling, J. K., Gutman, D. A., Zeh, T. R., Pagnoni, G., Berns, G. S., & Kilts, C. D. (2002). A neural basis for social cooperation. Neuron, 35, 395–405

External links[edit | edit source]