Personality is the study of individual differences, mostly in humans, though some work in animal personality too has happened. While evolution has designed for some universal adaptations, that lead to say human universals, evolution has also maintained some variations which leads to individual differences.
Personality traits are stable and consistent patterns of responding in terms of emotions, behavior, cognition and motivation across different situations. Various methods, both theoretical and empirical, have been used to arrive at the most parsimonious collection of traits; some of these methods include lexical studies to arrive at basic traits on which humans differ. Its important to remember that humans differ along degrees and on a continuum on these dimensions and the difference is not of kind or categories.
The most well known and well established personality trait model is the Big Five or the FFM which posits that humans differ on the following five dimensions: Extraversion, Neuroticism, Openness/Intellect, Agreeableness and Conscientiousness. The personality trait structure is hierarchical. There are meta traits of stability (Alpha) and plasticity (Beta) over the Big Five; there are aspects (two each) below the Big Five; and finally there are multiple facets composing each aspect.
If we want to explore the neural substrates of personality, we have to start at the description level and the Big Five is a good place to start. Next one needs to look at psychological functions behind each trait/ aspect and only then can one turn to what is known about brain structure/ function and neurochemical composition to figure out how those traits may be instantiated in the brain.
In explicating all this I will be hugely relying on Colin De Young and colleagues work and highly recommend listening to this podcast/ reading the mentioned papers (pdf, pdf). I will however be extending and building on that analysis.
First thing I would like to extend is that instead of the Big Five, I will be using the HEXACO model of personality which posits that there are six major traits of personality: Honesty-Humility, Emotionality, EXtraversion, Agreeableness, Conscientiousness and Openness/Intellect. The major difference from Big Five is the addition of a new factor Honesty-Humility and also that A(greeablness) of Big Five is not the same as A of HEXACO.
Now, Colin De Young and colleagues have proposed, and found evidence, for two aspects each in the Big Five (which they measure using BFAS) ; extending the same to HEXACO I propose two aspects that make Honesty-Humility: Honesty and Humility! Phew, that was easy!! I also propose to use the same aspect names Colin De Young and colleagues use for Big Five in below analysis which is extrapolated to the HEXACO.
I would also list down the possible functions of each aspect/trait and the possible neurotransmitters / brain regions associated with that trait/ aspect based on theoretical as well as empirical grounds.
But first lets talk a little more about stability and plasticity.
Stability is made up of Neuroticism (reverse scored) , Agreeableness and Conscientiousness. Stability involves sensitivity to unpredictability/ ambiguity. Neuroticism (reverse scored ) refers to emotional stability; Agreeableness refers to social stability (social harmony) while conscientiousness refers to motivational stability.
Plasticity is made up of Extraversion and Openness/Intellect and I propose that Honesty-Humility will also load on this factor when two factor analysis of personality is done. Plasticity is associated with exploration of the unknown. Extarversion involves behavioral exploration; openness/ intellect involves cognitive exploration and I propose that Honesty-Humility involves moral exploration (vs moral exploitation of others that is associated with Dark Triad/ Dark Tetrad which is associated with the low pole of Honesty -Humility). This is a testable prediction. Some work on creativity suggests that it is not associated with C/A/E but is positively associated with eXtraversion and Openness/ intellect and negatively associated with Honesty- humility. Thus H, X and O seem to go together in one way or the other!
Another important point to note is that stability is associated with serotonergic system while plasticity with dopaminergic system; this gives us the second prediction of the day: Honesty-humility which loads on plasticity should be associated with Dopamine in the brain.
So this brings us finally to the list of aspects along with their associated emotions (after all consistent emotional states leads to traits over time is one way to look at personality and I have been writing a series of posts regarding emotions and personality), and the neurotransmitters systems or associated brain systems/networks.
- eXtraversion : aspect Assertiveness. This is associated with emotion of courage/drive. The neural system underlying this aspect is proposed to be Behavioral Activation system (BAS as proposed by Gray ) . The value coding neurons of dopamine system will be associated with this.
- eXtraversion : aspect Enthusiasm. This is associated with emotion of Joy/Play. The neural system underlying this aspect is proposed to be Pleasure system (PS as proposed by me here ) . The endogenous opioid system will be associated with this, along with dopamine.
- Emotionality (Neuroticism) : aspect Withdrawal. This is associated with emotion of sadness. The neural system underlying this aspect is proposed to be Behavioral Inhibition system (BIS as proposed by Gray ) . The neurons of serotonin system will be associated with this.
- Emotionality (Neuroticism) : aspect Volatility. This is associated with emotion of fear. The neural system underlying this aspect is proposed to be Fight-flight-freeze system (FFFS as proposed by Gray and others) . The neurons of nor–epinephrine along with serotonin system will be associated with this.
- Openness/Intellect: aspect Openness. This is associated with emotion of awe/wonder. The neural system underlying this aspect is proposed to be Default Mode Network (DMN as proposed by many) . The neurons of salience coding dopamine system will be associated with this. Note that at times if you are very high on this trait, everything will seem salient and you may suffer from apophenia/ psychosis in extreme cases.
- Openness/Intellect: aspect Intellect. This is associated with emotion of Lust and sexual selection plays a big role in development of intelligence. The neural system underlying this aspect is proposed to be Fronto Parietal Control Network (FPCN as proposed by many) . The neurons of dopamine system are likely to be associated with this.
- Agreeableness: aspect Compassion. This is associated with emotion of disgust (negative correlation). The neural system underlying this aspect is proposed to be Empathy/ Mirror Neuron Network. The hormones of oxytocin have been associated with this. This is also associated with perception of Warmth when you first meet someone.
- Agreeableness: aspect Politeness. This is associated with emotion of Anger/Agression (negative correlation). The neural system underlying this aspect is proposed to be Social Dominance/ Power network. The hormones of testosterone have been associated with this. This is also associated with perception of Competence when you first meet someone. The serotonin system is also likely associated with this, given its role in aggression/ anger.
- Honesty- Humility: aspect Honesty. This is associated with emotion of Pride . More research needs to happen about its neural substrates.
- Honesty- Humility: aspect Humility. This is associated with emotion of Gratitude/ Contentment . More research needs to happen about its neural substrates.
- Conscientiousness: aspect: Industriousness. This is a uniquely human capacity (only other species where it may be present is chimpanzees). This is associated with emotion of Apathy (negative correlation). The neural system underlying this aspect is proposed to be Salience Network or Ventral Attention Network ( SAL/VAN) . Much less is known about neurochemical aspect except that Serotonin should be implicated.
- Conscientiousness: aspect: Orderliness. This is a uniquely human capacity (only other species where it may be present is chimpanzees). This is associated with emotion of Shame (negative correlation). The neural system underlying this aspect is proposed to be Dorasl Attention Network (DAN) . This is very speculative. Much less is known about neurochemical aspect except that Serotonin should be implicated.
The above is partly based on Colin De Young and colleagues work and partly some speculations, based on sound theoretical basis, by me. Even of some of the neural systems may not align with traits as mentioned above, I am very positive that at least the structure and functionality of personality traits is pretty much accurate. As always I am excited to live in such exciting times!
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