A dominant bodily fluid (“humour”) is associated with a personality type:

• Phlegm: Phlegmatic, quiet, unemotional
• Yellow bile: Choleric, impulsive, easily angered, irritable
• Blood: Sanguine, lively, optimistic, courageous
• Black bile: Melancholic, sad, depressive, pessimistic
  -> Perfect temperament would be balanced when all four exist equally

3 different body types:

• Ectomorphs - thin, leaner fragile bodies, introverted, self-conscious
• Mesomorphs - muscular and rectangular body, aggressive, courageous
• Endomorphs - well rounded bodies, tolerant, pleasant, likeable, want others to like them

Phrenology → personality traits are found to be localised and related to different brain structures, which vary in their volume (DeYoung et al., 2010)

Criminal personality → People are likely to differentiate criminal faces from non-criminal faces (Valla et al., 2011)

3 main areas:

• 1) Anatomy of the CNS
• 2) Biochemistry (hormones, neurotransmitters)
• 3) Genes and evolution

Amygdala - overactive amygdala associated with:

• Anxiety, fear
• Neuroticism
• BPD
• Negative emotions such as anger and fear
• Important role in computing the degree to which a stimulus offers impending threat or reward

Assumed:
“A greater-than-average volume of a specific brain structure may signify greater-than-average power to carry out specific functions associated with that structure, on the assumption that larger populations of neurons can produce larger outputs and can therefore be more influential than smaller populations of neurons.”

Findings
Significant relationships between different brain regions and personality traits

• Neuroticism - associated with a few different areas e.g. posterior hippocampus and dorsomedial PFC, many regions appear to be involved in emotion regulation, threat, and punishment sensitivity
• Conscientiousness - middle frontal gyrus was more developed among people who were high in conscientiousness
• Similar for extraversion
• Agreeableness - associated with less volume in posterior CC (on the right) and more volume on the STS (left)

Norepinephrine - fight or flight responses

• Is both a neurotransmitter and a hormone but mainly acts as a neurotransmitter
• Associated with neuroticism
• Brain concentrated on source of threat in fight or flight - with higher levels of norepinephrine we are more likely to be neurotic

• Oxytocin - love hormone. Associated with less agression
• Another hormone in the stress-response cascade
• In females, promotes nurturant and sociable behaviour along with relaxation and reduction of fear (the opposite of fight or flight)
• Causes people to be less fearful

Correlation ≠ causation
Research suggests changes in the environment and life experiences can affect changes in biochemistry
e.g. increase in testosterone in women with 'male dominated' jobs

Emotional Stability (inverse of neuroticism)

• Neurotransmitter: serotonin
• Hormones: cortisol, norepinephrine
• Brain structures: right frontal lobe (withdrawal), left frontal lobe (anger), amygdala, insular anterior cingulate

Agreeableness
Neurotransmitter: serotonin
Brain structures: left dorsalateral prefrontal cortex, superior temporal sulcus, posterior cingulate cortex

Extraversion

• Neurotransmitter: Dopamine
• Hormones: endorphins
• Brain Structures: medial orbito-frontal cortex, nucleus accumbens, amygdala, striatum
  

COMT - encodes a protein that breaks down the neurotransmitters dopamine, epinephrine, and norepinephrine
Extraversion and reasoning abilities

• Related to increased dopamine in PFC which leads to increased extraversion and reasoning ability

Many SNPs are combined into genome-wide polygenic scores (GPS)

• GPS (in relation to a particular trait) is an individual score that can be used to predict genetic influences on personality traits - e.g. find out scores for different kinds of GPS e.g. neuroticism which can then be correlated with a measure for neuroticism
  
  

Genetic variants have been found to be associated with traits related to happiness, depression, and anxiety

• Evolutionary psychologists believe that those characteristics that helped humans survive are more likely to be present in future generations
• Adaptive value is context dependent
• Certain personality traits are adaptive in certain contexts but not in others

• Retained some degree of mental functioning
• However, his personality was fundamentally changed
• Became irrevent, impateint, rude, obstinate
• Inability to understand the emotions of others, and to appropriately regulate own impulses and feelings

Perfect example of genotype-environment interaction: the genotype is important, but only for people who have experienced a certain kind of environment

Somatic marker hypothesis
Damasio (1994); emotions enable people to make decisions that maximise good outcomes and minimise bad ones, and to focus on what is really important

The frontal lobes are centres of cognitive control, serving to anticipate the future and plan for it

One recent theory proposes that two fundamental dimensions of personality - stability and plasticity - organise the traits of the Big Five into two groups.
A large amount of evidence suggests that the dopaminergic system is the foundation of plasticity, defined as a "general tendency to explore and engage with possibilities"

Market for SSRIs may be more than $20bn per year in the US

• These pills are not 'happy pills' but seem to make negative emotions less severe whilst leaving positive emotions unaffected

For most traits:

• The estimates of heritability garnered from studies of family resemblance that don't include twins average about 20% or half the average heritability estimed from twin studies
• That is, estimates of heritability based on twin studies assume that individual genes and the environment act independently to influence personality, and these influences can simply be added up
• But, genes can operate differently depending on the other genes that are present - genes will express themselves in different ways in different environments
• As a result, while heritability estimates based on twins may be too high, those based on broader family relationships may be too low

Major meta-analysis concluded that the environment shared by siblings growing up was important in the development of several types of psychopathology during the period between childhood and adolescence:

• Including conduct disorder, rebelliousness, anxiety, and depression
• Only exception was ADHD which for the shared family environment did not seem to matter

Thousands of different genes are probably involved in complex traits such as sensation seeking or proneness to anxiety. The chance of finding a single gene that has a simple, direct, and easily understood effect on impulsiveness, anxiety or any other aspect of personality is virtually nil

Active person environment = 'niche picking' people tend to select and create environments that are compatible with and may magnify their genetically influences tendencies

Reactive person environment = the same environments that promoe good outcomes for some people can promote bad outcomes for others and vice versa