The Neuroscience of Personality

Plan for the Two Weeks:

Yesterday: Advanced EEG methods and general applications in psychology
Today: The neuroscience of personality (and how EEG has contributed)
Next week: Laboratory training in using EEG

Plan for Today:

How neuroscience and personality became intertwined.
How Eysenck devised a “science of personality.”
How Gray optimised Eysenck’s work for neuroscience.
How Gray’s theory is still being tested to this day.

Quick Recap from Last Week:

Specifically, what EEG is in two slides.

EEG in Two Slides:

EEG aims to record the electrical activity of the brain.
From electrodes placed on the participant’s scalp.
By looking at changes in electrical voltage-over-time (Event related potentials) and frequency (spectral analysis) we can link brain activity to psychological states.

Eysenck's Science of Personality

Quick History for Context:

Who is Eysenck?
- In pre-World War Two Germany, Eysenck was an up and coming physicist about to study at Berlin University.
- However, not being too keen on the political direction of Hitler’s Germany, Eysenck left for France, but he wasn’t too keen on France either.
- So he traveled to London, where he intended to study Physics.
- However, because of, in his words, “Bureaucratic stupidity” he was told that he would have to study psychology instead.
- This admin problem might have been distressing for Eysenck but it ended up being a massive boon for Psychology as Eysenck went on to radically change the field.
Eysenck’s theories and Eysenck himself have been described as:
- “A contrarian.”
- “A heretic.”
- “A romantic.”
- “Playing with fire.”
- It has been argued that almost every psychologist in Eysenck’s era had a strong opinion of his work and of the man himself.
- Furthermore, he described himself as: “… a big friendly dog that gets kicked in the teeth because of the reception of original ideas received by other people.”
Eysenck noted that different people responded in different ways to the same stimuli.
- Person X might react with happiness to the sight of a melon, whereas person Y might respond with anger.
- Eysenck argued that it was mostly personality which (a) decided how the person reacted and (b) explained the differences between people.
- Furthermore, he argued that personality could be understood by statistically grouping dozens of little factors (i.e. shyness, hatred of melons) into large dimensions of personality.
- Eysenck argued that this grouping of factors could create a science of personality.
- This ruffled the feathers of some theorists of the time who thought that personality was non-scientific.
- Corr (2016) has a theory about what led Eysenck to this realization. Corr noted that Eysenck grew up in a time when people had to make serious and life-changing decisions (i.e. Nazi Germany). Corr theorized that Eysenck noted different people making different choices to these difficult decisions, even when their situations appeared to be the same.
Eysenck argued that his dimensions of personality were mostly driven by biological factors.
- That is, the differences in how people react to stimuli should be largely determined by genetic and phenotypic (the body made by the genes) factors.
- In particular, Eysenck theorized that someone’s neurological makeup would have a significant impact on their personality.
- More specifically, Eysenck argued there should be a set of neural structures for each dimension of personality.
- In Eysenck’s own words: “We may say that personality is the central concept in our theory. The distal cause is DNA, the proximal cause is the physiological, hormonal, neurological set of intermediaries linking DNA to behavior, and interacting with environmental factors. (Eysenck, 1993).
What were Eysenck’s dimensions of personality and how did he generate them?
- Eysenck started this work at Mill Hill hospital, London.
- Specifically, he collected details on men who were “war neurotics” (soldiers who had suffered nervous breakdowns during training and had subsequently not been able to go to war).
- He wanted to statistically group the details (or factors) that tended to be present in men who became war neurotics and those who did not.
- This followed his aim of understanding why different people responded differently to the same situation (war training).
- Over several decades, Eysenck continued to statistically group factors from a range of populations and situations, until he had developed two scientific dimensions of personality.
Eysenck’s Dimensions:
- The first dimension developed by Eysenck was Introversion-Extraversion.
- The second was Neuroticism.
- In the middle of each dimension is normalcy (statistically average).
- To the outer of each dimension is abnormality and moving towards clinical levels of the trait (especially for neuroticism).
- But Eysenck also argued there was a biological and neurological system behind every dimension – so is there?
- There are other dimensions but we will be focussing on these two today because they are the ones that are best grounded in neuroscience.
Research with drugs has provided some validation of Eysenck’s dimensions and their biological underpinnings.
- For example, Munkelt (1965) gave participants a mild tranquilizer (meprobamate) and assessed its effects on various cognitive tests.
- However, the results were non-significant – it appeared that the drug and placebo groups did not differ significantly.
- Munkelt noticed that there was a huge amount of variation in the scores of participants and suspected that personality could be influencing their responses to the drug.
- To test this, Munkelt (1965) also split participants into high and low neuroticism groups.
High and low neuroticism participants seemed to have almost opposite reactions to the drug:
- This supports Eysenck’s arguments that:
  - One stimulus does not create the same reaction in every participant - you need to account for personality.
  - As a drug was used as the stimulus, there is likely a biological mechanism controlling the variations in personality.
Another two examples from Janke (1964):
- In both cases, high and low neuroticism participants appear to respond differently to certain drugs (although, interestingly, not at all doses).
Heritability studies further suggest that Eysenck’s dimensions have a biological root:
- For the neuroticism factor, evidence from twin studies suggests that neuroticism is 30%-50% heritable. (Birley et al., 2006; Floderus-Myrhed, Pendersen & Rasmuson, 1980)
- The extraversion factor has been estimated to be even more heritable at 53% (Jang, Livesley & Vemon, 1996).
- However, the single nucleotide polymorphisms (genes) that explain this heritability are proving difficult to find (Calboli et al., 2010; Lukaszewski & Roney 2015).
The Introversion/Extraversion dimension was the closest Eysenck came to a neurological explanation of his dimensions.
- Specifically, he noted that there were distinct differences in how susceptible introverts and extraverts were to arousal following a Galvanic skin response (sweat as a proxy for autonomic system arousal).
Subsequently, introverts would be more likely to avoid additional arousal whereas extraverts would seek it out.
- This led to the identification of different optimal learning environments for introverts and extraverts.
- Subsequently, Eysenck proposed that introverts and extraverts were differentiated by the sensitivity of the brain system which processes arousal.
- Extraverts are more likely to seek additional arousal.
- Introverts are more likely to avoid additional arousal.
Eysenck mapped the dimension of introversion-extraversion to the sensitivity of the ascending reticular activating system (ARAS).
- The reticular activating system works in two ways:
  - It’s ascending branch takes sensory information and projects it to the cerebral cortex for processing.
  - It’s descending branch takes commands from the brain and projects them to the spinal cord (and then to the muscles).
So increased sensitivity of the ascending tract would let in more sensory signals to the higher centers of the brain.
- Subsequently, introverts can let in ‘too many’ sensory signals and become over stimulated/aroused easily (and so seek to avoid further stimulation).
- Conversely, extraverts can let in ‘too few’ sensory signals and become under stimulated (and so seek out further stimulation).
That’s about as far as anyone got in terms of linking Eysenck’s personality dimensions to neurology.
- So Eysenck’s neurology of personality pretty much amounted to – Some people’s brains are more sensitive than others.
- No groups of specific brain structures were (reliably) linked to each dimension.
- No specific wavebands of electrical activity were (reliably) linked to each dimension.
- No subtle brain processes were (reliably) linked to each dimension.
- No single nucleotide polymorphisms have been linked to each dimension.

Gray’s Reinforcement Sensitivity Theory

Who is Jeffrey Gray?
- Gray was Eysenck’s star pupil.
- The main direction of his work was to adapt Eysenck’s scientific theory of personality to make it more neurologically sound.
- Specifically, he wanted to identify two dimensions of personality, each of which with separate and well defined neurological systems.
By rotating Eysenck’s factors by 30 degrees, Gray created the personality dimensions of punishment sensitivity and reward sensitivity.
Gray had developed a more in depth research approach to identifying the neurological systems of each dimension: Give drugs to mice
Gray successfully identified personality dimensions made up of specific neurological structures, neurological processes and behaviors.
RST has been updated several times. This is the most recent (Gray & McNaughton, 2000; McNaughton & Corr, 2004) version.
- Specifically, for the punishment sensitivity dimension, Grey proposed two neurological systems.
- Each system responds to a different type of punishing stimuli and motivates a different set of defensive behaviors:
  - A) The Fight Flight Freeze System
  - B) The Behavioral Inhibition System
- Conversely, for the reward dimension, Grey proposed one neurological system.
- The system has its own neurological structures and set of approach behaviors:
  - C) The Behavioral Activation System
Punishment sensitivity – Fight Flight Freeze System (FFFS)
- A set of neurological structures driven by the periaqueductal gray.
- The structures respond to aversive (punishing) stimuli of all kinds by motivating Escape behaviors and fear.
- High FFFS people could be more Fearful, avoid danger and be more Vulnerable to phobias.
Reward Sensitivity – Behavioral Approach System (BAS)
- A set of neurological structures driven by dopamine channels in the brain.
- The BAS responds to appetitive (rewarding stimuli) by motivating hope, joy and approaching behaviors.
- High BAS people could be more driven to succeed, more prone to addiction and more impulsive.
Thirdly, the system that we are going to focus on today - the Behavioral Inhibition System (BIS).
- Punishment sensitivity part two - The Behavioral Inhibition System (BIS) is a set of neurological structures driven by the septo-hippocampal system and controlled by the theta waveband (This will be important later).
- The BIS is thought to be sensitive to, and to try to resolve, Goal conflict.
- Most commonly, the BIS deals with fights between the FFFS (avoid) and the BAS (approach) over what to do.
- So people with a more sensitive BIS are prone to detecting Goal conflict where there is none.
- So if you are the type of Person who is not very decisive and always finds it tough to make Up your mind – then you probably have a sensitive BIS.
- The subjective experience of having your BIS activated is thought to be rumination (“what Should I do”?) and anxiety.
- The BIS can also detect and resolve conflict between BAS/BAS (which tasty food to eat) or FFFS/FFFS (should I run or fight) goals.
Most commonly, Gray determined the behaviors and neurological structures of each dimension by giving rodents (mice & rats) drugs.
Blanchard and Blanchard (1990) started with a mouse in a cage with a safe hiding place. They then placed some mouse food elsewhere in the cage. When the mouse went to get the food, the Blanchards added either:
- A) The smell of a cat (potential threat)
- B) An actual cat (definite threat)
In condition A, the mouse had a fairly strong approach goal (approach the food) and a fairly strong avoid goal (avoid the place that might have a cat in). This should have caused a Goal conflict over whether to risk it or not.
- The mouse displayed risk assessment (sniffing air) and hesitant behaviors.
- In condition B, the mouse had a fairly strong approach goal (approach the food) and a very strong avoidance goal (don’t get eaten but the cat. This should have caused a strong avoidance motivation (FFFS).
- The mouse displayed fleeing, defensive fight and freezing behaviors.
Crucially, the effects of drugs were different in both scenarios:
- Anxiolytic (anti-anxiety) drugs reduced these behaviors.
- Panicolytic (anti-panic) drugs reduced these behaviors.
The Behavioral Inhibition System (BIS) is a punishment sensitivity system which Gray thought of as an anxiety system.
- He noted that one class of drugs, anxiolytics, reduce anxiety in humans.
- He classified included any behaviors which are reduced by anxiolytics can be grouped as anxiety (BIS) behaviors, as we saw in the study on the previous slides.
- More interestingly though, he argued that any brain structures which are impaired by anxiolytics can be grouped as anxiety (BIS) brain structures as well.
- When you put two together, Gray argued, you get a brain-behavior system of anxiety – which he named the BIS.
- This follows Eysenck’s approach of statistically grouping factors into dimensions. Except Grey is using drugs to group behaviors and brain structures.
- So Eysenck started from nothing and grouped factors into dimensions (top-down). Conversely, Grey started from the dimensions (punishment-anxiety) and then found the behaviors and brain structures which fit the dimension (bottom-up).
Gray could group these behaviors as anxiety behaviors (i.e. BIS behaviors).
And these behaviors as fear/panic behaviors (i.e. FFFS behaviors).
Gray noted that the activity of the septo- hippocampal system was inhibited by anxiolytic (anti-anxiety drugs).
The septo-hippocampal system is part of the limbic system found within the temporal lobe.
- One of the most important features of the hippocampus is its use of theta rhythmicity.
- That is – activation of the hippocampus produces theta wave electrical activity.
- The septum acts as a pacemaker for the hippocampus – by stimulating the septum you can control the amount of theta generated by the hippocampus.
- So normal hippocampal functioning involves a lot of theta activity.
Gray noted that anxiolytic (anti-anxiety) drugs impair the functioning of the septum and reduce the amount of theta produced by the hippocampus
- Gray could include the septo-hippocampal system in the BIS.
- This also gave theta activity a large role in the BIS.
- In fact, the effects of anxiolytics on the septo-hippocampal system were very consistent and pronounced.
- Furthermore, the septo-hippocampal system seemed to be controlling the other regions of the BIS via the theta waveband.
- Therefore, Gray placed the septo-hippocampal system as the core of the BIS – the most important part – and placed Theta as a major ‘calling card’ of BIS involvement.
So, anti-anxiety drugs reduced a set of behaviors (goal-conflict initiated risk assessment and hesitation) and impaired a set of brain structures (driven by the septo-hippocampal system).
- Gray could therefore link these into the brain-behavioral system of anxiety, known as the BIS.
- However, Gray didn’t stop there. He also identified a further link between the septo-hippocampal system and goal conflict behaviors using lesion studies (in rodents).
Specifically, Gray demonstrated that lesions (destructive damage) to the septo-hippocampal system produced the same effects as anti-anxiety drugs.
- That is, damaging these structures resulted in a reduction of goal conflict behaviors (risk assessment and hesitation).
- So Gray was able to again show that these neurological structures and behaviors could be grouped.
If they respond to anxiolytics – they’re BIS, if they respond to panicolytics – they’re FFFS.
We’ve now identified neurological structures in the brain that correspond to the BIS system, which controls how anxious someone is. But how do we bring it back to personality, like Eysenck did? Can we show that people who are more anxious have more sensitive BIS brain structures?

Linking Personality to RST:

I am often preoccupied with unpleasant thoughts.
I feel sad when I suffer even minor setbacks.
I sometimes feel ‘blue’ for no good reason.
When feeling ‘down’, I tend to stay away from people.
I have often spent a lot of time on my own to “get away from it all”.
The thought of mistakes in my work worries me.
When nervous, I sometimes find my thoughts are interrupted.
You just answered a set of self-report questions designed to measure how sensitive the BIS systems are in your brain…
… but do scores on that test actually correspond to neurological activity coming from the BIS?
Time to go back to our old friend, EEG for some answers!
Lockhart et al. 2019 No relationship between trait BIS and EEG BIS
Neo et al. 2011 Trait anxiety and neuroticism significantly correlated with EEG BIS
Shadli et al. 2015 Trait neuroticism significantly correlated with EEG BIS
Moore et al., 2012 Trait BIS significantly correlated with EEG BIS
What other ways could we link it to personality in the future?
We could demonstrate that changes in anxious behaviours correspond with EEG BIS activity in humans..
But how? More on this next week, when we go through your EEG lab training and think about how we might use it to answer this question.

Conclusions:

Eysenck pioneered much of the early work on personality and neuroscience using statistical grouping methods and work on the ARAS.
However, Eysenck struggled to get his theory of personality to link to the brain outside of the ARAS
Gray built this into a wider neurological theory that encompassed many more brain areas
However, those testing Gray’s theory are now having difficulty linking those areas back with the original personality measures…
Which we’ll try out for ourselves next week!