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Inheritance of Personality (Biological) - Coggle Diagram
Inheritance of Personality (Biological)
Heritability: The proportion of phenotypic variance that is attributable to genotypic variance
Personality traits: 50% of variance is due to genetic factors
Mean twin correlation of 0.54
Partitioning of variance
Genes
Shared environment: Anything that makes twins the same. Contribution is trivial (at most 5%)
Non-shared environment: Anything that makes twins different
It's very difficult to tease out non-shared environment variance and random error. But this is more important (45%)
First law: Everything is heritable
"g": As children grow up, they increasingly modify and create their own learning experiences due to genetic predispositions
Marriage: 68% heritability
Population concepts
: Cannot be applied to a single individual
Methods
Twin studies: **Heritability = 2(r mono - r di)
Adoption studies
Molecular genetics
Genome-wide association (GWA) studies
Dopamine D4 receptor gene (DRD4): Shortage of dopamine cause yearning for stimulation to the point of risky behaviour. Linked with impulsivity, novelty seeking, ADHD. Results are inconsistent.
Dopamine is the reward and motivation system
Serotonin transporter gene (5-HTT): People with short 5-HTT alleles are higher on N and showed stronger responses when exposed to aversive and threatening stimuli
Serotonin regulates mood
Note that individual genes account for very small effects. Complex contributions of at least 2-3 genes to single trait.
Gene-environment correlation: Individuals with different genes have differential exposure to different environments
Passive: Parents provide both genes and environment to children, and children did nothing to obtain environment
Reactive: Parents and others respond to children differently depending on the child's genotype
Active: Person with specific genotype creates or seeks out a specific environment
The heritability for assaultive trauma exposure is higher than non-assaultive trauma exposure. People with certain personality traits are more likely to self-select risky environments, which increases their risk of assaultive trauma exposure.
We can create environments that we are in through reactive and active gene-environment processes. So even environmental measures can show genetic influences (0.3)
Gene-environment interaction: Individuals with different genotypes have differential responses to the same environments
Abused children with low levels of MAOA (monoamine oxidase A) frequently develop conduct disorders, while those with high levels of MAOA far less likely to develop antisocial personalities
Brain and behaviour
Methods: Case studies of brain damage, brain stimulation, brain imaging
Brain anatomy and personality
Amygdala: Emotional experiences, assesses threat or reward
Different reactivity: 0.71 with extraversion and amygdala activation when participants were presented with happy faces
Different structure: Extraverts have higher concentration of grey matter in left amygdala while neurotics have lower concentration in right amygdala
Prefrontal cortex: Executive system of the brain in charge of higher cognitive and emotional functions
Damage can result in deficiency in emotional experience and impaired decision making
Social interaction and cooperation
Interconnections in brain region
Capgras Syndrome: Disconnect between visual system and amydgala leads to seeing a loved one but having no emotional feelings toward them
Biochemistry and personality
Nervous system
Epinephrine (PNS) and Norepinephrine (CNS): Activates the fight-or-flight. High on N have overactive norepinephrine system
Dopamine: Reward-orientation. Behavioural activation system (BAS)
Serotonin: Inhibition of behavioural and emotional impulses. Low levels can result in negative emotional symptoms
Prozac blocks the reuptake of serotonin
Paroxetine (similar to Prozac) make individuals feel less negative emotions and more sociable
Hormones: Biochemicals that affect the body in a different location from where it is produced released by the hypothalamus, gonads, and adrenal cortex
Testosterone: Sex hormone implicated in aggression
Positively associated to sociability, impulsivity, dominance
Testosterone-aggression relation complex: High testosterone does not mean individuals are aggressive
2D: 4D ratio
High: Ring < Index
Low: Ring > Index
More exposure to prenatal testosterone. Associated with risk-taking, sensation seeking, social dominance, etc.
Oxytocin: The "love" hormone for social bonding
Prairie vole vs Meadow vole: Genetically identical except that prairie vole releases more oxytocin. Prairie voles bond for life as they release more oxytocin and vasopressin
Biologically-based personality theories
Eysenck's biologically-based personality dimensions: The PEN model (psychoticism, extraversion, neuroticism)
Ascending Recticular Activating System (ARAS) used to be a gateway through which neural stimulation entered the cortex. Resting arousal level is low if the gateway is closed. Introverts have a higher resting arousal level (gateway is open) than extraverts and seek out low-stimulating arousal settings
BUT later findings showed that its the
arousability
rather than resting level of ARAS that differentiates extraverts and introverts. At moderate level of stimulation, introverts show enhanced physiological reactivity than extraverts
Gray's reinforcement sensitivity theory: 2 conceptual brain systems (independent) that regulate approach-avoidance behaviours
Behavioural Inhibition System (BIS): Stop system (avoidance behaviour) sensitive to cues of punishment and uncertainty
More aligned with neuroticism
Septo-hippocampal system with close link to serotonergic pathway
Behavioural Activation System (BAS): Go system (impulsivity) sensitive to cues of reward and incentive
More aligned with extraversion
Dopaminergic system
Zuckerman's Sensation Seeking: People who have a high need for sensation are less tolerant of sensory deprivation
Monoamine Oxidase (MAO): Brakes of the nervous system
Lower levels --> high sensation seekers
Genetically-mediated environments
Environment measures also have genetic influences: Heritability of .30
Through reactive gene-environment correlation
Through active gene-environment correlation