Tag Archives: HEXACO

The Neural Substrates of Personality

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.

  1. 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.
  2. 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.
  3. 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.
  4. 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 norepinephrine along with serotonin system will be associated with this.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. Honesty- Humility: aspect Honesty. This is associated with emotion of Pride . More research needs to happen about its neural substrates.
  10. Honesty- Humility: aspect Humility. This is associated with emotion of Gratitude/ Contentment . More research needs to happen about its neural substrates.
  11. 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.
  12. 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!

The ABCD of Personality Structure

Regular readers of The Mouse Trap would be aware of my ABCD model of psychology whereby all psychological phenomena are explained in terms of Affective, Behavioral, Cognitive and Dynamic/Desire dimensions.

Personality Traits from SignalPatterns.com

Personality Traits from SignalPatterns.com (Photo credit: Wikipedia)

The affective dimensions is also related to sensory processes; the behavioral dimension to motor processes; the cognitive dimension to associative processes and the desire/dynamic/motives dimension to social processes.

We are increasingly focusing on brain as a means to study psychological phenomena and thus four major divisions of neurosciences are affective neurosciences, behavioral neurosciences, social neurosciences and cognitive neurosciences.

Now, I have written extensively about personality, especially in relation to emotions, and have written a series of posts about the structure of personality traits and the underlying basic emotions. I have also tangentially touched upon or used ABCD and the fundamental four model while coming up with those previous posts; but today’s post is exclusively focused on the ABCD model and its utility for delineating personality traits.

Before we move onto personality traits, lets refresh our knowledge of brain structure. As per a controversial theory of brain structure, by Paul McLean, brain can be divided into a reptilian brain,a paleomammalian brain/ limbic brain and a neomammilain brain/neocortex; for our purpose the details of the model need not be true. However, one thing that McLean postulated was that older brain regions are in control of newer regions and if newer brain regions malfunction/ do not exercise control the behavior due to older system may get activated. Hughlings Jackson had surmised the same earlier and this is the part I will be focusing on.

Consider an earlier brain part that controls movement; (this may be mostly instinctual responding or impulsive initiation) ; a later brain part may inhibit and lead to better response/ proactive action that is well considered/ planned. I will call these two instances bottom-up effects and top-down effects on movement respectively.

With this in mind lets start a deeper look at the ABCD.

  1. Affective/sensory: This would be related to detecting unexpected stimuli or looking out for expected stimuli.
    1. The bottom up process of detecting incoming stimuli is enhanced by level of arousal. High arousal leads to better detection and low arousal to lesser detection; people may differ in their natural arousal levels and I guess you know where I am going with this-the introversion- eXtraversion dimension.
    2. The top down process of looking out for (potentially harmful) stimuli may lead to worry or anxiety. High Anxiety may help in vigilant detection, while lower anxiety to lapses in detecting harmful stimuli; the natural variation in this may be the trait Emotionally stable-Neuroticism( Emotionality). Anxiety remember was one of the dimensions discovered by Gray as relevant to personality.
  2. Behavioral/Motor:   This would be related to initiating action or responding to stimuli.
    1. The bottom up process here would lead to Impulsivity , another dimension elaborated on by Gray. The personality trait relevant here would be Impulsive Sensation Seeking as defined by Zuckerman.
    2. The top down process here would lead to Inhibition; when that process does not work, the low pole would be disinhibition (which is distinct from impulsivity). In FFM/HEXACO , this trait may be labeled as Conscientiousness and is related to strength of self-regulation.
  3. Drives/Social:  This would be related to interactions with others and the motives behind them – either to help others or the reciprocate a previous help.
    1. The bottom up process here is reactive reciprocation; or aggression in case of deception/defection by the other. The one end of this pole will be characterized by Aggression and hostility while the other pole by nice and reciprocal behavior and this leads us right on to Agreeableness dimension.
    2. The top down or expectation driven process here would be trusting and helping others on the one pole (in hope of reciprocation) and manipulating, hurting or exploiting people on the other. this naturally leads us to Honesty-humility dimension of HEXACO and the opposite pole that I believe is the dark tetrad of sadism, Machiavellianism, narcissism and sadism.
  4. Cognitive/ associative : This would be related to the tendency to make and use broad vis–vis narrow associations while doing information processing.
    1. The bottom up process here could be related to distractibility vis-a-vis focus. Some people may be easily distracted/ form loose associations and this may lead to Openness to experience in them; others may be more closed to new information. I think of this as the encoding process.
    2. The top down process here could be related to imagining novel associations between concepts etc. I would say this is a new dimension called Imagination dimension (Scott Barry Kaufman would be happy to hear:-)) .  At one end would be daydreamers and creative folks , at the other end more pragmatic/ reality oriented folks. I relate this to retrieval process. As this trait may still be evolving, we see psychosis related to this- imaginations/ top down processes overpowering reality orientation. this may also explain the association of creativity and mental illness.


I am happy with this personality structure organization with eight traits, instead of the usual five, that I have come up with. It has a solid theoretical rationale and a lot of thinking has gone into it; of course empirical work will prove whether its true or not and whether it stands the test of time!!

The Evolution of Altruism And Its Relationship to Personality

Altruism, put simply, is helping others or cooperating with others, even if it is costly to self. Of course, something like that cannot evolve, unless there are benefits too, associated with such acts of apparent selflessness.

Evolutionary theory mandates that there be some genetic payoffs in terms of either inclusive fitness or future benefits to self (reciprocity) for any kind of altruism/ cooperation to evolve.

I recommend reading Wikipedia articles on reciprocity, kin selection, and evolution of cooperation if they are not familiar to you or you need a refresher.

Cooperation, to start with, can evolve based on three forms of reciprocity: direct, indirect and network. All are based on the fact that there re repeated interactions between group of people- dyads, triads or many more. Reciprocity can typically be measured in the lab using the repeated Dictator/ Trust game.

Direct reciprocity was proposed by Robert Trivers as a mechanism for the evolution of cooperation. If there are repeated encounters between the same two players in an evolutionary game in which each of them can choose either to “cooperate” or “defect”, then a strategy of mutual cooperation may be favoured even if it pays each player, in the short term, to defect when the other cooperates.

Here, in direct reciprocity A trusts/helps B and hopes that when time comes B will reciprocate/help A. The top-of-the-mind factor is whether or not to trust somebody and whether or not to reciprocate someone’s trust. Trust and exploitation may be relevant issues here. In the Dictator/ Trust game this trust/exploitation manifests as the amount that is split and given to the other person vs kept with oneself.

In the standard framework of indirect reciprocity, there are randomly chosen pairwise encounters between members of a population; the same two individuals need not meet again. One individual acts as donor, the other as recipient. The donor can decide whether or not to cooperate. The interaction is observed by a subset of the population who might inform others. Reputation allows evolution of cooperation by indirect reciprocity.

This is partially correct that reputation for being trustworthy helps in indirect reciprocity; however that is only true for the downstream version; for the upstream version feelings of gratitude/happiness/awe/elevation in persons receiving the help/ witnessing the act also lead to more pro-social behavior by those receiving help/ witnessing. Thus feelings of gratitude/ awe/elevation mediate this kind of upstream indirect reciprocity. See below for upstream and downstream variants.

Individual acts of indirect reciprocity may be classified as “upstream” or “downstream”:

  • Upstream reciprocity occurs when an act of altruism causes the recipient to perform a later act of altruism in the benefit of a third party. In other words: A helps B, which then motivates B to help C.

  • Downstream reciprocity occurs when the performer of an act of altruism is more likely to be the recipient of a later act of altruism. In other words: A helps B, making it more likely that C will later help A.

Before touching upon network reciprocity, I will take a quick detour about kin selection. I believe kin selection or inclusive fitness is also a type of reciprocity (that between related individuals sharing genes) and may be rechristened genetic reciprocity. After all if A is likely to help B because they share x % of genes, the reverse is equally true and applicable. And of course this is mediated by emotional attachment to the kid/kin.

As per one definition of kin selection:

A biological theory stating that a gene that causes an organism to exhibit behavior detrimental to its survival will increase in frequency in a population if that behavior benefits the organism’s relatives, which will pass the gene on to subsequent generations.

If I slightly change words form above definition, I can now define a neighbor selection process as a cultural theory stating that a meme that causes an organism to exhibit behavior detrimental to its survival will increase in frequency in a population if that behavior benefits the organism’s neighbors, which will pass the meme on to subsequent neighbors.

We are now ready to look at network reciprocity:

Real populations are not well mixed, but have spatial structures or social networks which imply that some individuals interact more often than others. One approach of capturing this effect is evolutionary graph theory, in which individuals occupy the vertices of a graph. The edges determine who interacts with whom. If a cooperator pays a cost, c, for each neighbor to receive a benefit, b, and defectors have no costs, and their neighbors receive no benefits, network reciprocity can favor cooperation.

Basically, what I understand from the above is that if you help your neighbors sometimes such that the cost is not too high but benefits to neighbors are high and if  cost to benefit compares favorably with average number of neighbors/ neighborly interactions you have, then in the long run you will benefit and this form of cooperation can evolve.  To me the effects are mediated by the number of neighbors or sociability of a person.

Of course, even if you have all these mechanisms in place, cooperation may not evolve, as you may have free-riders. One important mechanism that has evolved to keep the free-riders in check is that of punishment. And once punishment is part of the picture you don’t even need repeated interactions, one-off games may be sufficient. I call this phenomenon Direct Punishment. One way it has been measured is with the Ultimatum game.

In the Ultimatum game, the second player can inflict costly punishment on first player by refusing to accept the division; this costly punishment is dyadic in nature and the aggression/hostility/vengefulness of the second player ensures that cooperation in even one-off encounters happens.

Basically instead of trusting and helping B, A starts by exploiting B and B retaliates by punishing A at cost to oneself.

Of course one can then surmise that there can be a phenomena of indirect punishment. This again may happen in two ways:

  1. Indirect punishment upstream: A is exploitative in nature; A exploits B; B punishes A, who then feels guilt/ gets reformed and stops exploiting C or even starts helping C.
  2. Indirect punishment downstream: A is exploitative in nature: A exploits B, B punishes A; B gets a reputation for being tough/competent and stops getting exploited by others say C or C may now even help B.

The Indirect reciprocity effects can be seen in Public goods/ trust game.

I will now take a detour and introduce the HEXACO model of personality which set me thinking about this in the first place.

HEXACO is an alternate personality model that is based on the same principles as the Big Five/FFM; i.e. it uses factor analysis of lexical terms in various languages to arrive at major personality traits.

The six factors are generally named Honesty-Humility (H), Emotionality (E), Extraversion (X), Agreeableness (A), Conscientiousness (C), and Openness to Experience (O). The personality-descriptive adjectives that typically belong to these six groups are as follows:

  • Honesty-Humility (H): sincere, honest, faithful, loyal, modest/unassuming versus sly, deceitful, greedy, pretentious, hypocritical, boastful, pompous

  • Emotionality (E): emotional, oversensitive, sentimental, fearful, anxious, vulnerable versus brave, tough, independent, self-assured, stable

  • Extraversion (X): outgoing, lively, extraverted, sociable, talkative, cheerful, active versus shy, passive, withdrawn, introverted, quiet, reserved

  • Agreeableness (A): patient, tolerant, peaceful, mild, agreeable, lenient, gentle versus ill-tempered, quarrelsome, stubborn, choleric

  • Conscientiousness (C): organized, disciplined, diligent, careful, thorough, precise versus sloppy, negligent, reckless, lazy, irresponsible, absent-minded

  • Openness to Experience (O): intellectual, creative, unconventional, innovative, ironic versus shallow, unimaginative, conventional

The factor H is a new factor not present in Big Five/FFM. The E though looking similar to N of big Five, is conceptually different; it no longer contains anger/hostility which are instead present in HEXACO A. similalrly there are important differences between HEXACO A and Big Five A. the other 3, C, O and X (extarversion) are similarly conceptualized and defined in both systems and have same loadings when tested together.

Ashton and Lee, the proponents of the HEXACO model, have themselves related evolution of altruism to these traits [pdf] and I am building on their work.

Basically as per them,

To begin, we have proposed that the Honesty- Humility and Agreeableness factors represent two complementary aspects of the construct of reciprocal altruism (Trivers, 1971). Honesty-Humility represents the tendency to be fair and genuine in dealing with others, in the sense of cooperating with others even when one might exploit them without suffering retaliation. Agreeableness represents the tendency to be forgiving and tolerant of others, in the sense of cooperating with others even when one might be suffering exploitation by them. (For a discussion of two broadly similar, although not identical, constructs, see Perugini, Gallucci, Presaghi, & Ercolani, 2003.) Presumably, high levels of Honesty- Humility are associated with decreased opportunities for personal gains from the exploitation of others but also with decreased risks of losses from withdrawal of cooperation by others. In a similar manner, high levels of Agreeableness are associated with increased opportunities for personal gains from long-run reciprocal cooperation with others, as well as with increased risks of losses from exploitation by others. (Note that we use the term altruism in terms of a dimension of altruistic versus antagonistic tendency, which involves both a willingness to help or provide benefits to others and an unwillingness to harm or impose costs on others.)
In addition, we have proposed that Emotionality represents tendencies relevant to the construct of kin altruism (Hamilton, 1964), including not only empathic concern and emotional attachment toward close others (who tend to be one’s kin) but also the harm-avoidant and help-seeking behaviors that are associated with investment in kin (see also Lee & Ashton, 2004). Presumably, high levels of Emotionality are associated with increased likelihood of personal and kin survival, as well as with decreased opportunities for gains that are often associated with risks to personal and kin survival.
To me, this looks like equating direct reciprocity with H and direct punishment with A.  With this in mind I now list the personality trait (HEXACO)/ evolution of altruism linkages.
1. Kin Selection/ Genetic Reciprocity : mediated by emotional attachments etc and related to Emotioanlity.
2. Neighbor Selection / Network Reciprocity: mediated by sociability and related to sociability aspects of Extrarversion.
3. Direct Reciprocity : mediated by trusting others and being honest and related to Honesty-humility.
4. Direct Punishment:  mediated by punishing others and being aggressive/ hostile when needed and related to Agreeablness.
5. Indirect Reciprocity upstream:  mediated by feelings of gratitude/ awe/ elevation and possibly related to Openness to Experience
6. Indirect Punishment upstream: mediated by feelings of guilt/responsibility and related to Conscientiousness.
 7. Indirect Reciprocity downstream: mediated by signaling and being trustworthy; need a new personality dimension for this.
8. Indirect Punishment downstream: mediated by signaling and being competent/ tough and possibly related to Surgency dimension of Extarversion.
I am more and more convinced, looking at the above model that we evolved to be cooperative/ altruistic rather than otherwise.