Differential

• Differential psychology looks at the differences between individuals

  • Individuals differ significantly
  • Differences are typically stable
  • Aim to measure differences and understand causes and consequences of these differences
  • Looking at variation - measure, understand, and predict
• Causal explanations for individual differences:

  • Brain structure and brain activity
  • Genetic influences
  • Hormone-related, neuropeptide-related influences
  • Socioeconomic influences
  • Environmental stressors
• Methodologies and Approaches

  • Hormones (blood stream, long lasting), neuropeptides (brain, intermediate, affect neurons not adjacent), neurotransmitters (signalling between two neurons)
  • Receptors and signalling machinery
  • Genes - code for proteins making up the receptors/involved in signalling
  • Neurogenetics - studying genes relevant to workings of the brain and nervous system
• Modes of measurement:

  • Behavioural tasks
  • Questionnaires and psychometrics
  • Neuroimaging
  • Biological assays (levels of hormones/neuropeptides/neurotransmitters)
• Ways to affect neuronal signal transmission:

  • Presynaptic ways: release more transmitter, deplete transmitter stores, more effective vesicle fusion, reuptake transporter changes, autoreceptor changes
  • Postsynaptic ways: more receptors near membrane, more effective receptors, affect one step in many-step signalling cascade, affect messenger from postsynaptic neuron to presynaptic neuron
• Genetics

  • Gene is a strand of DNA typically coding for a protein, transcribed into mRNA which is transferred to a particular protein
  • Many polymorphisms of a genes, springing from mutations
  • Sequencing DNA can allow us to look at alleles (polymorphisms of one or more genes)
  • Many alleles may result in same phenotype - risk alleles are a version of a genes associated with a higher risk of certain condition
  • Single nucleotide polymorphisms (SNPs) comprise most common form of genetic differences
  • Outcomes can be driven by genes, environment, and an interaction
• The effects of oxytocin and vasopressin can be summarised as 'prosocial', promoting maternal/paternal behaviour, attachment in young, social recognition, sexual behaviour, pair and social bonding, empathy, Theory of Mind, interpersonal warmth, trust, and reduction of anxiety
• Individual differences in humans in vasopressin and oxytocin:

  • Walum et al., (2008) - if both copies of the vasopressin receptor 1a gene are a particular variant allele, your marriage is of a poorer quality
  • Bartels and Zeki (2004) - fMRI, neuroimaging subtraction technique -> activation from looking at partner or child minus looking at another's partner or child = core brain activations underlying romantic and parental love
  • Both types of attachment activate areas specific to and overlapping in brain's reward system coinciding with areas rich in oxytocin and vasopressin receptors
• Prosocial behaviour: Vasopressin/oxytocin and insights from animal work

  • Monogamous prairie vole -> partake in biparental care, part of the <5% of mammals who are monogamous, team up as economic unit?
  • Compared to meadow voles that are solitary and polygamous
  • Oxytocin receptor density increased in nucleus accumbens, caudate, putamen, and PFC in monogamous voles compared to rats, mice, and non-monogamous meadow voles (Ross and Young, 2009)
  • Oxytocin release: prairie vole mating and vaginocervival stimulation in rats and sheep
• Prosocial behaviour: Oxytocin insights from animal work

  • Blocking oxytocin receptor activity in receptor-rich regions in monogamous prairie voles (Ross and Young, 2009)
  • Observed how long they 'huddled' next to a mate compared to a 'stranger'
  • Increased preference for partner in control and caudate/putamen groups
  • No increased preference in nucleus accumbens and PFC -> oxytocin receptors in these regions required for adult pair bonding
• Prosocial behaviour: oxytocin/vasopressin peaks in humans:

  • Vasopressin peaks at arousal then falls back to baseline -> appetitive like dopaminergic signal in nucleus accumbens - wanting?
  • Oxytocin peaks at ejaculation then slowly falls back to baseline -> more towards 'satisfaction; and like an opioidergic signal - liking?
  • Opioid antagonist (naloxone) block the release of oxytocin after orgasm and subjective pleasure in females
  • Some evidence of subjective intensity of orgasm in females and oxytocin release
  • Oxytocin important in bond formation -> prevalent at a sensitive time
• Prosocial behaviour - attachment and vasopressin

  • Lim et al., (2004) - artificial over-expression of vasopressin receptor in ventral pallidum of promiscuous meadow vole
  • Increased number of vasopressin 1A receptors on post-synaptic membranes
  • Marked increase of partner-specific huddling compared to stranger
  • Higher V1a receptor density increases adult pair bonding
• Prosocial behaviour - oxytocin/vasopressin and pair bonding in voles

  • Variation in receptor activity controls strength of pair bonding - blocking receptors eliminates post-coital huddling, increased density increases post-coital huddling
  • Vole studies do not examine individual differences: look at species differences and experimentally-induced (exogenous) differences
  • Individual differences in humans -> observe naturally occurring, endogenous variation -> differences in signal (levels of neuropeptides) and responses to signal (genes)
• Prosocial behaviour - individual differences in humans: vasopressin and marriage

  • Walum et al., (2008) - genetic variation of vasopressin receptor 1a gene in the RS3 polymorphism -> 334 risk allele
  • Males (together for >5 years) measured on partner bonding scale with serious marital threat question and marital status record
  • 0 copies of risk allele -> strong bonding
  • 2 alleles - 'less strong bonding;
  • Partner Bonding scale - 48 > 45.5 -> .0004
  • Marital Crisis - 15% < 34% -> .008
  • Married - 83% > 68% -> .01
• Prosocial behaviour - individual differences in humans: vasopressin and marriage

  • Walum et al., (2008) - Women said relationships with men with >1 copy were of a lower quality - affection, dyadic consensus and cohesion
  • Men with >1 copy: less likely to get married, more likely to experience serious threat, show less-bonded relationship, female reports less quality
  • Vasopressin has a more selective role in regulating male side of bonding -> similar to animal model
  • Some evidence 334 associated with increased activation of amygdala and is 'over-transmitted' in those with autism
• Prosocial behaviour - individual differences in humans: oxytocin

  • Ditzen et al., (2009) - participants trying to resolve an artificial couple conflict, coded on positive and negative behaviours, those given oxytocin showed more positive behaviour with exogenous variation, cortisol levels reduced
• Prosocial behaviour - individual differences in humans: oxytocin

  • Gonzaga et al., (2006) - women recounted and relived positive emotion of love/infatuation with male partner present, non-verbal behaviour frequency and duration was coded as affiliative or sexual
  • Romantic display and duration strongly correlated with oxytocin release - no correlation with sexual displays
  • Oxytocin signal also correlated with strength of pair bond
  • Oxytocin release may support romantic behaviour - causality unclear, may be affiliation, not 'love'
• Prosocial behaviour: testosterone opposes oxytocin/vasopressin

  • oxytocin/vasopressin - cooperative, monogamy, quality of bond, commitment, reduced aggression
  • Testosterone - competitive, polygamy, quantity of mates, higher aggression
  • Both strategies are not evolutionarily stable:
  • High T: children die too young - influx of high oxt/vasp due to children surviving and reproducing
  • High oxt/vasp - highly vulnerable to high T strategy
  • Humans exhibit both alongside individual differences
• Prosocial behaviour: testosterone lower in adult pair bonds

  • Predisposition - high T man chooses to not get married/have kids
  • Experience - romantic and paternal activity actively lowers T
  • Grey et al., (2002) - marriage and fatherhood associated with lower T in males (cross-sectional)
  • Burnham et al., (2003) - men in committed romantic relationships have lower T -> married and parents significantly lower than just married/paired or unpaired
• Prosocial behaviour: variation in T signals predicts pair bonding differences

  • Booth and Dabbs - controlled for age and different facets of marriage -> high T men more likely to not get married, 2x as likely to divorce, and ~2x as likely to be unfaithful
  • Effort spent on mating mediated by T, effort spent on parenting mediated by oxytocin
• Prosocial behaviour - variation in T in lesbian first-time mothers

  • Chin et al., (2020) - prenatal T (12, 20, 28, 36w) and postnatal questionnaire (3m) about relationship and parenting
  • Birth mothers - higher relationship satisfaction when partner had lower T
  • Non-birth mothers - support and relationship commitment when partners had lower T, support, higher relationship satisfaction, commitment, and investment if they had lower T
  • Lower T seems to be better for pro-social and bonding behaviours
  • Non-birth mothers did not show prenatal changes in T unlike men -> more commitment prior
• Prosocial behaviour - interactions between biology and environment

  • Heritability of T -> Correlation in MZ twins > DZ twins (higher in men)
  • Some genetic determinants - neuropeptide or hormone signals are not purely genetically determined
  • Abuse lowers oxytocin - female oxytocin lower compared to controls (Heim, 2009) -> may be due to genetics
  • Low-loving interactions gradually reduces oxytocin
  • Protective mechanisms 'shuts down' normal levels of prosocial responsiveness
  • High levels of childhood maltreatment - prosocial predisposition from allele for oxytocin receptor becomes maladaptive
• Making people more prosocial:

  • Make people come together more -> enhance rewards and decrease stress
  • "Social buffering" - animals reduce stress by being with one another
  • Improve outcomes of interaction - enhance memory (reciprocal altruism, efficiency, remembered), trust, and empathy (cognitive and emotional)
  • Could predict that oxytocin and vasopressin promote these
  • Measure social interactions objectively (implied/actual interaction) and self-report
• Frequency and Closeness of Social Interaction:

  • Oxytocin underlies prosocial effects of MDMA -> Thompson (2007), activated oxytocin-containing hypothalamic neurons, increasing oxytocin in plasma, more huddling in rats; Wolff (2006), MDMA increases plasma oxytocin and vasopressin
  • Oxytocin-receptor antagonist blunts the pro-social effects of MDMA
  • Oxytocin promotes 'social approach' -> increased sociality and reduced avoidance
• Beneficial Outcomes from Social Interaction - Memory for Social Identity

  • Tested rats -> success depends on accurate perception and memory for another's olfactory signature -> when given OT, rats spent more time exploring new rat -> increased sociality and memory
  • Vasopressin and mice -> normally, male mice decrease investigating familiar female, and increase when it is a stranger.
  • Knocking out vasopressin receptor V1aR gene severely impairs social recognition (Bielsky, 2004)
  • Lateral spetum is a crucial brain region for V1aR-mediated social recognition (Bielsky, 2005)
• Beneficial Outcomes from Social Interaction - Trust

  • Kosfeld (2005) - intranasal OT increased trust in investors where trustee could betray investor - effect only when investor knew trustee was a real person
  • fMRI - oxytocin promoted trust even after betrayal, reduced amygdala activation and increased caudate (rewards/decision making) activation (both dense in oxytocin receptors)
• Beneficial Outcomes from Social Interaction - Empathy

  • Guastella (2008) - tracked eye movements of males looking at neutral faces after being given OT -> increased fixations and gaze time for eyes, reduction in forehead/cheek.
  • Oxytocin biases attention toward 'mind-reading relevant' sensory input
  • 'Reading the Mind in the Eyes' (Baron-Cohen, 2001) - seeing eyes, ASD Ps score significantly worse than controls, inverse correlation between score and Autism Spectrum Quotient (r = -0.53)
  • Eyes are a good test of empathy and can be used to measure exogenous changes
• Beneficial Outcomes from Social Interaction - Empathy

  • Domes (2007) - exogenous increases in oxytocin enhance mentalising from pictures of humans' eye region
  • Oxytocin promotes fixation and gaze upon eye region - enhances the ability to interpret and to infer mental states from the eye region -> oxytocin promotes cognitive empathy
  • Endogenous variation (Rodriguez, 2009) -> gene coding for oxytocin receptor -> 3 aspects of empathy: perspective taking (cognitive), empathetic concern (emotional), fantasy (combination). People with GG allele get more answers correct compared to AA/AG allele
• Parenting - Oxytocin and Individual Differences

  • Gordon (2010) - measured oxytocin and interactions in first postpartum weeks and at 6m
  • Affectionate (positive affect, motherese, affectionate touch) vs stimulatory (proprioceptive/stimulatory touch, object presentation) play
  • Parental oxytocin increased in first 6m - no difference between parents, interdependence and stability
  • Maternal OT -> affectionate play; Paternal OT -> stimulatory play
• Parenting - Oxytocin and Individual Differences

  • Touch (Feldman, 2012) - polymorphisms in oxytocin-related genes, positive correlation in both parents -> higher level of oxytocin, more they touch their babies
  • More oxytocin and low-risk alleles is better
  • Gaze synchrony (Feldman, 2012) - high OT levels and low-risk CD38 allele = longest gaze synchrony
• Parenting - Testosterone and Individual Differences

  • Predisposition or experience? (Muller, 2009) -> T declines in men performing high level of paternal care compared to those doing minimal fathering: Tanzanian groups - high levels of paternal care associated with decreased T in Hadza foragers compared to no differences in fathers/non-fathers in Datoga pastoralists
  • Heritable -> correlation in MZ twins, genetic heritability (h^2 = ~.6)
  • Environment -> age (low as child, higher as young adult, decreases as older); relationship (lower in long-term); fatherhood (lower in high-caring)
• Parenting - Testosterone and Individual Differences

  • Mascaro - testicular volume inversely correlated with nurturing-related brain activity in human fathers
  • Weisman (2014) - interactions between OXT and T and parent-child interaction - intranasal oxytocin
  • Higher baseline T -> less time spent affectionately touching, gazing towards, speaking motherese to, and overall time spent with baby.
  • Oxytocin-induced change in T correlated with parent-child social behaviour - positive affect, social gaze, touch, vocal synchrony
• Gray's (1982) 3 motivational systems of personality:

  1. Behavioural Approach/Activation System -> mediates reaction to appetitive stimuli -> impulsivity
  2. The more sensitive to reward cues you are, the more you want them (approach, acquire, learning about cues). Experience of anticipation can be rewarding
  3. Behavioural Inhibition System -> mediates reaction to punishing stimuli
  4. The more sensitive to punishment you are, the more you avoid
  5. Fight/flight/freezing system
• Gray's Theory of Personality

  • BIS and BAS are orthogonal -> free to vary and don't predict each other
  • BIS and BAS are stable aspects of personality relating to motivation
  • BAS/SR - motivate to approach and consume rewards
  • BIS/SP - inhibition, caution to avoid dangers
  • Degree to which systems are activated vary across individual
  • Activity should be measurable and predict individual differences in behaviour
  • Grey argues much of human personality can be explained through these two independent motivating systems, related to positive and negative reinforcement
• Gray's Theory of Personality - Measurements: Carver and White (1994)'s BIS/BAS

  • Behavioural Activation System:
  • Reward Responsiveness
  • Drive - persistent pursuit of desired goals
  • Fun Seeking - desire for new rewards, willingness to approach a potentially rewarding event in the spur of the moment
  • Questionnaires should have stability and should not be redundant
  • Takahashi et al., (2007) -> heritability in MZ twins - 0.28-0.35
  • Test-retest high - stability over 2-3 years -> BIS = 0.63; BAS = 0.59
  • Orthogonality -> low correlation: time 1, r = 0.06; time 2, r - 0.03
• Gray's Theory of Personality - Measurements: Torrubia et al., (2001)'s SPSRQ

  • Sensitivity to Punishment - behavioural inhibition in situations with the possibility of aversive consequences or novelty; worry or cognitive processes produced by threat of punishment/failure
  • Sensitivity to Reward - questions about situations in which people could do something to obtain rewards
  • Large sample > 1500
  • Internal consistency - >0.75
  • Test-retest stability - >0.57 -> declines as time interval increases
  • Orthogonality -> -0.05 to +0.08
• Gray's Theory of Personality - Brain Activity in BAS: Dopamine

  • Pfaus (1990) - dopamine increase when rat sees a receptive female -> rises at anticipation of pleasures
  • Fiorino (1997) - appetitive increase -> highest at first copulation, decreases, slight increase when novel female shown
  • Wanting - mediated by nucleus accumbens - dopamine
  • Appetitive stages -> wanting and anticipating. Reward prediction error in incentive salience. DA-rich regions in all reward regions
  • Liking - mediated by NA opioids
  • Consummatory stages, hedonic pleasures, opioid-rich regions include NA and central pallidum
• Gray's Theory of Personality - Brain Activity in BAS

  • Key regions - ventral tegmental nucleus, ventral striatum (nucleus accumbens), amygdala, ventral pallidum, orbitofrontal cortex
  • Money: Hahn (2009) -> brain activity when anticipating reward: right ventral striatum, right OFC -> activity with large reward positively correlated with SR score
  • Food: Franken and Muris (2005) - SR, FCQ-T (food craving), and BMI
  • SR correlated with BMI and food craving (r = 0.31/0.32)
  • FCQ-T correlated with BMI at r = 0.24 -> SR predicts BMI better
  • BAS predicted long-term behaviour (BMI) and food cravings
• Gray's Theory of Personality - Brain Activity in BAS

  • Beaver et al., (2006) - BAS Drive and response to food stimuli
  • Increased activation in reward regions (ventral striatum/NA, OFC, ventral pallidum, amygdala) correlated with increased BAS drive score
  • Individual variation in trait reward sensitivity highly correlated with activation in reward areas to images of appetising food
  • Weydmann (2022) -> SR and BAS, responses to food cues
  • Implicit -> 70% of results significant
  • Hedonic -> 87.5% of results significant in expected direction
• Gray's Theory of Personality - BAS and extroversion

  • More extroverted individuals have stronger reward-related brain activity (functional) and have larger reward-related brain regions (structural)
  • Cohen (2005) - extraversion scores positively correlated with activity in reward-related regions -> measures activity when getting reward vs not -> risk alleles for dopamine receptors blunt reward response
  • DeYoung (2010) - degree to which you are extroverted positively correlated with volume of orbitofrontal cortex