Lecture 25: The Neurobiology of Love & Attachment

Question 1

neurobiological view of attachment

Answer 1

• There is no single attachment system dedicated exclusively to the formation of social bonds
• Rather, a set of more general purpose affective-emotional systems for which attachments emerge with learning
  (ex. Separation distress, Felt security and social pleasure, Motivation to seek out & engage with close others)

Question 2

Affective neuroscience

Answer 2

a branch of neuroscience focused on understanding emotions in humans & other mammals

Question 3

Emotions

Answer 3

complex psychological states involving physiological changes, subjective experience, and behaviours/expression

Question 4

Affect

Answer 4

the subjective experience of emotion

Question 5

Key assumptions of affective neuroscience

Answer 5

1. Emotions & associated feelings evolved to serve specific purposes in relation to biologically significant and life-challenging situations
2. Felt aspects of emotional systems (affects) serve 3 key adaptive purposes

Question 6

3 adaptive purposes of pheromones

Answer 6

• Highlight survival & reproductive issues in the environment
• Motivate behaviour for survival & reproduction
• Aid in memory construction through reinforcement

Question 7

current neurobiological research

Answer 7

• Much of the research pertains to animals
• May not generalize perfectly to humans
• Ex. humans appear to lack dedicated neural machinery for detecting pheromones

Question 8

social pain

Answer 8

• Distress we experience when important social ties are threatened or lost
• Often, we use physical pain words to describe such experiences
• This tendency is cross-cultural
• The propensity to feel social pain may be rooted in separation distress children experience when separated from the caregiver; generalized to maintaining other social relationships given the benefits of group living

Question 9

evolution of social pain

Answer 9

• May have evolved from general pain mechanisms
• Pain serves an important adaptive purpose: it captures our attention & demands action
• Individuals with congenital insensitivity to pain are highly susceptible to physical injury have reduced life spans (often die in childhood)
• For highly vulnerable infants, being left alone is a life-or-death situation
• Experiences of social pain motivate behaviour to re-establish proximity with caregiver

Question 10

two components of pain

Answer 10

1. sensory component
2. affective/motivational components

Question 11

sensory component of pain

Answer 11

• Specific information about what’s happening
• What, where, how intense is it?
• Involves the somatosensory cortex

Question 12

affective/motivational component of pain

Answer 12

• The aversiveness of the experience & motivation to stop it
• The alarm component
• Involves a different set of neural regions (ex. Dorsal anterior cingulate cortex (dACC) anterior insula (AI))
• Activation in some areas (ex. dACC) may trigger physiological stress response

Question 13

social pain in the brain

Answer 13

• Increased activation in the affective pain regions (ex. dACC, AI) during various kinds of social pain experiences, like
  1. Reminders of deceased for bereaved individuals
  2. Reminders of ex-partners for those who had been recently dumped
  3. Social exclusion: Strength of the activation is correlated with feelings of rejection/exclusion
• Interestingly, some studies have observed activation in the somatosensory cortex as well

Question 14

interoception

Answer 14

• Ability to perceive signals originating within the body
• Ex. breathing, hunger, thirst
• Crucial for being able to maintain a steady internal state

Question 15

insula

Answer 15

• Plays a key role in processing these signals & imbuing them with emotional & motivational significance
• Ex. may interpret signals of sympathetic nervous system activation as anxiety

Question 16

types of mechanoreceptors in the skin

Answer 16

fast-conducting & slow-conducting mechanoreceptors

Question 17

fast-conducting mechanoreceptors

Answer 17

allow for fine discrimination

Question 18

slow-conducting mechanoreceptors

Answer 18

• Respond to low-pressure, low-velocity tactile stimulation (ex. Slow and light stroking)
• This type of stimulation is typically found in intimate affiliative interactions and is experienced as subjectively pleasant
• Signal travels directly to the insula (may serve an all-clear signal)

Question 19

felt security

Answer 19

• Once contact with caregiver is regained, experience strong feelings of pleasure & comfort
• Reinforces the attachment bond
• In adulthood, symbolic proximity-seeking may be sufficient to restore the sense of comfort & security
• Some parallels to the literature on physical pain & placebos: cognitive factors like mere expectation of pain relief can alleviate pain

Question 20

pain relief as a reward

Answer 20

• Relief from pain (i.e. omission/reduction of an aversive event/punishment) is more than simply an attenuation of pain; it is rewarding & pleasurable
• Pleasure of relief is derived from the violation of negative expectancy
• `Pessimists (who generally hold more negative expectations) experience greater dread of adverse event & greater relief when the adverse event is avoided

Question 21

endogenous opioid system

Answer 21

system of opioid receptors & their respective ligands (chemical messengers that bind to a receptor)

Question 22

μ-opioid receptors

Answer 22

• Bind drugs like morphine & heroin, mediate their analgesic & rewarding effects
• Normally bind internally produced (endogenous) chemical messengers like β-endorphin
• Play an important role in pain relief, placebo effects, hedonic responses to rewards like food

Question 23

Brain opioid theory of social attachment (BOTSA)

Answer 23

• Opioids mediate attachment through dual mechanisms
• Declining levels of opioids during separation contribute to social pain/separation distress
• Increasing levels of opioids during reunion contribute to feelings of reward & comfort

Question 24

receptor agonist

Answer 24

chemical substance that binds to & activates a certain receptor

Question 25

receptor antagonist

Answer 25

• Chemical substance that binds to & blocks a certain receptor, thereby blocking or dampening normal biological responses
• Seeing how typical behavioural responses change after the administration of an antagonist allows us to infer the neurochemical mechanisms behind the typical response
• Naloxone & naltrexone are common opioid receptor antagonists

Question 26

BOTSA Hypothesis 1

Answer 26

if separation distress reflects state of endogenous opioid withdrawal, stimulation of opioid activity should diminish behavioural manifestations of separation distress (e.g., distress vocalizations (DVs), clinging)

Question 27

pharmacological approach to BOTSA hypothesis 1

Answer 27

activation of μ-opioid receptor agonists like morphine or β-endorphin reduce DVs & proximity-seeking behaviour like clinging in variety of non-human animals species

Question 28

brain-stimulation approach to BOTSA Hypothesis 1

Answer 28

• Electric stimulation of the periventricular gray (PVG) produces the release of β-endorphin, physical analgesia, and the reduction of DVs in isolated guinea pigs.
• Both analgesia & education in DVs can be reverse with the administration of an opioid receptor antagonist (naloxone)

Question 29

BOTSA hypothesis 2a

Answer 29

social contact leads to the release of endogenous opioids

Question 30

evidence for BOTSA hypothesis 2a

Answer 30

Large increases in cerebrospinal fluid concentration of β-endorphin following grooming in monkeys

Question 31

BOTSA hypothesis 2b

Answer 31

If this release of endogenous opioids mediates (drives) the comforting effects of social contact, should be able to block the comforting effects of social contact by blocking endogenous opioids

Question 32

evidence for BOTSA Hypothesis 2b

Answer 32

Young animals treated with opioid receptor antagonists like naltrexone continue to cry & cling to mom even after reunion

Question 33

further BOTSA animal evidence

Answer 33

• Further evidence that opioids mediate the formation of attachment bonds
• Genetic knock-down of the μ-opioid receptor in mouse pups causes deficits in attachment
• Oprm - - pups emit fewer separation distress calls relative to wild-type controls (oprm + +)
• Do not develop preference for the mother’s olfactory cues (in contrast to wild-type controls)
• Attachment & separation distress go hand-in-hand: the pain of separation is the price we pay for attachment

Question 34

indirect evidence for BOTSA in human research

Answer 34

• Social contact decreases physical pain in real-life (e.g., heel lance in infants, labour) and experimental settings
• Even viewing picture of a loved one decreases pain during lab task
• However, not clear if this is opioid-mediated

Question 35

imaging evidence for BOTSA in human research

Answer 35

When thinking of an experience of social loss, deactivation of opioid neurotransmission in regions to pain affect

Question 36

pharmacological evidence for BOTSA in human research

Answer 36

• Naltrexone (vs. placebo control) decreases feelings of warmth & connection participants experience while reading affectionate notes from close others or looking at their photographs. Also decrease activity in the left ventral striatum (reward-related region of the brain) while looking at pictures of close others
• Participants received naltrexone or placebo before completing a self-disclosure task. There was no effect on feelings of closeness toward partner, but blocked the increases in positive affect and self-esteem that placebo participants experienced after the task. This suggests that opioids may contribute to positive feelings we experience in different kinds of affiliative situations

Question 37

OPRM1 A118G

Answer 37

linked to variation in both physical pain sensitivity & rejection sensitivity (the G allele being the sensitive variant)

Question 38

genetic evidence for BOTSA in human research

Answer 38

• Couples filled out a questionnaire after each interaction they had over a period of 3 weeks
• Found that individuals carrying at least 1 copy of the G allele reported steeper declines in felt security when their partner behaved more coldly or hurtfully towards them than usual

Question 39

implications of opioid research

Answer 39

Opioid drugs may be a substitute for unmet belonging needs

Question 40

oxytocin

Answer 40

• A neurochemical messenger that plays a key role in parturition & lactation, is released during copulation
• Also postulated to play an important role in social behaviour & bonding
• Has received more research attention (in humans) than opioids, but their precise function still remains unclear

Question 41

oxytocin research in animals

Answer 41

• Early evidence indicating that oxytocin may play a role in social bonding came from the comparison of two closely related species with very different social structures
• Prairie voles: typically form pair bonds after mating, exhibit biparental care
• Montane voles: live in isolation, no evidence of pair bonding
• Different responses to separation in infancy: prairie voles respond with DVs and stress hormone secretion; montane voles do not exhibit behavioural/physiological reaction
• Prairie voles have high density of oxytocin receptors in regions related to reward & reinforcement (nucleus accumbens), whereas montone voles have few receptors in these areas
• Can facilitate partner bonding in prairie voles by injecting exogenous oxytocin (even if the voles have not mated)
• Oxytocin receptor antagonist blocks partner preference formation following matin in prairie vole

Question 42

initial oxytocin research in humans

Answer 42

• First study to examine social effects of oxytocin in humans found that intranasal oxytocin increases trust during an economic trust game
• A subsequent flurry of research found many prosocial effects:
  emotional recognition & empathy, generosity & cooperation, more positive communication behaviours during couple conflict discussions, increases in social motivation

Question 43

subsequent oxytocin research in humans

Answer 43

• As research accumulated, it became clear that the effects of oxytocin are not always consistent
• Some studies found no effects, very small effects, or negative/antisocial effects
• Ex. oxytocin actually decreases trust towards out-group members ad those with clinically high levels of rejection sensitivity (borderline personality disorder)
• Effects of oxytocin may depend on interpersonal & intrapersonal context

Question 44

Social salience hypothesis

Answer 44

oxytocin may focus attention on social cues

Question 45

evidence for the social salience hypothesis

Answer 45

• Oxytocin has been found to increase gaze to the eye region & lead to changes in functional connectivity among brain regions indicative of the heightened attention
• In mice, oxytocin enables maternal care behaviour (pup retrieval) by fine-tuning neurons in the auditory cortex so pup distress calls become more salient

Question 46

psychological/behavioural effects of increased social salience

Answer 46

• Psychological/behavioural effects of increased social salience will depend on contextual factors
• Might magnify prosociality when dealing with close or trusted others
• But, diminish prosociality when the situation or the individual’s disposition biases them to construe social information negatively
• Ex. oxytocin administration makes individuals low in attachment anxiety remember their mom as more caring & close; opposite effect for individuals high in attachment anxiety

Question 47

fMRI passion study

Answer 47

• fMRI study of early-stage intense romantic love (dating 7 months on average)
• While in the scanner, they viewed photos of a loved and familiar acquaintance
• Activation of the ventral tegmental area and related regions that receive projections from this area
• Part of the dopamine reward pathway
• Note: fMRI does not allow for measuring activity of a specific neurotransmitter, but other research has found increased dopamine release in these regions in response to rewards like money

Question 48

replicating fMRI passion study

Answer 48

• Finding since replicated cross-culturally and with same-sex couples
• Also replicated in long-term marriages who reported being still “madly in love” with their spouses
• Replicated using stronger control condition (close, long-term friend)
• Activity in the VTA correlates with feelings of passionate love
• But, not with scores on friendship-based love scale

Question 49

dopamine

Answer 49

• Commonly described as a “reward neurochemistry”
• Contributes to the incentive/motivation to pursue rewards
  (wanting vs. liking distinction)
• Unlike opioids, does not appear to mediate the pleasure of sensation
• At the affective level, this may be experienced as anticipatory exhilaration, eagerness, and euphoria
• Allows animals to pursue various rewards important for survival
• Responds to incentives in the environment and imbalances in homeostatic needs
• May contribute to the experience of passionate, romantic love; but likely also plays a role in attachment figures and care behaviour

Question 50

case of Leonard L

Answer 50

• Childhood encephalitis led to a destruction of dopamine brain circuits
• After being treated with L-DOPA (precursor of dopamine), able to experience a sense of engagement with the world, energy, and excitement