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How are personality traits – such as optimism, sensation seeking or need for cognition – "encoded" in the brain?

Do people with different levels of, say, extraversion have different neuronal structures? Or do they have different amounts of certain neurochemicals, different numbers of receptors, or other kinds of functional differences?

So if you want to change a trait, can you simply stimulate or supplement neuronal functionality, e.g. by administering the lacking neurochemicals, or do you have to "destroy" and "rebuild" the neuronal structure, e.g. through learning?

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As with anything in learning, whatever you do (weather it be attitude, thinking, behavior, or skills) - the more you do it, the stronger the neuron connections that support that ability are. For an entrepreneur, working so much begins to harden in his brain structure, so it's easier to keep it up. –  Ivan Ivković Apr 2 at 16:04
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Its two questions, could you split it? (Knowing how something is encoded does not mean that we know how to change it. For example, we know that some diseases are "encoded" in viri, but we cannot cure them.) –  Piotr Migdal Apr 2 at 18:14
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The "second part" is not about how to change it, but about where to aim. If you know that a desease is caused by a virus, you might not know how to treat it, but you know where the treatment has to aim: on the virus. –  what Apr 2 at 19:07

3 Answers 3

up vote 3 down vote accepted

Cool question...really huge though. I'll have to revisit this as I find time to add more. For starters, I just saw an interesting link in @ForbiddenOverseer's question, "Is there any Personality theory that uses scientific methodology instead of subjective interpretations?" For some info on cerebral blood flow and extraversion, check out Johnson and colleagues (1999). Here's an excerpt of the abstract:

RESULTS: Overall, introversion was associated with increased blood flow in the frontal lobes and in the anterior thalamus. Regions in the anterior cingulate gyrus, the temporal lobes, and the posterior thalamus were found to be correlated with extraversion. CONCLUSIONS: The findings of the study lend support to the notion that introversion is associated with increased activity in frontal lobe regions. Moreover, the study suggests that individual differences in introversion and extraversion are related to differences in a fronto-striato-thalamic circuit.

In an earlier answer today (to What makes a sight or an image mesmerizing and irresistible?), I implied that sensation-seeking relates to the behavioral activation system, the nucleus accumbens and VTA, and dopamine. Support for those relationships ought to be available through Wikipedia.

Here's a summary of other info from my lecture on biopsych for my class on personality a few years ago:

  • Frontal lobe
    • Activity has been correlated to negative emotionality via fMRI.
    • Cooperative people show more activity during social interaction, implicating reward sensitivity.
    • Aversive attention and motivation is right lateralized; approach motivation and aversion inhibition is left lateralized.
    • Transcranial magnetic stimulation (TMS) knocks out self-enhancement bias temporarily.
    • Damage reduces emotional experience, regulation, and inhibition – cf. Phineas Gage, Capgras syndrome, and the history of frontal lobotomies.
  • Amygdala
    • Implicated in identification of rewards & threats
      • Activates in extraverts receiving pleasant stimuli (e.g., happy faces, scenes, & emotion words; pleasant tastes)
      • Activates during social attraction; generates sexual responsiveness
      • Activates in shy people viewing unfamiliar faces
      • Also in pessimists when shown a picture of a snake
      • Overactive in people with anxiety disorders such as PTSD
    • Activated by unexpected emotional conflict – stronger in neurotics viewing conflicting cues.
    • Inhibited by anterior cingulate – cf. brain tumor in Charles Whitman, UT tower sniper ’66
      • “I have been a victim of many unusual and irrational thoughts. These thoughts constantly recur, and it requires a tremendous mental effort to concentrate on useful and productive tasks.”
  • Ascending reticular activating system – acts like a valve on incoming stimulation
    • More “wide open” (active) in introverts
      • Stronger reaction to lemon juice stimulus
      • Faster responses to noises in brainstem via EEG
    • Reaction to erotica, violence, mutilation, insects, etc.:
      • High sensation-seeking: arousal and reward area activation
      • Low sensation-seeking: emotional self-control area activation
    • Electrode stimulation of substantia nigra $\rightarrow$ depression!
    • Governs reactivity, not baseline arousal
      • Optimal arousal threshold is the same distance from rest regardless of extraversion
      • ARAS affects acceleration from stimulation toward the threshold. See simplistic figure:
        A simplistic figure I made a few years ago

I've got a few answers here on neurotransmitters and hormones already:

Judging from effects of TMS (and tDCS), intelligence may relate to cortical excitability and myelination – see "Can learning be facilitated by transcranial magnetic stimulation?" As for changing personality in general, neuroplasticity may be important to consider, but biofeedback may be able to take advantage of it to alter neuroticism – see "Neuroplasticity and Treatment of Depression". Chronic malnutrition might even affect neuroticism by deeper mechanisms than subjective stress resulting directly from deprivation – see "The effect of proper food intake on emotions and brain function". Other links seem to exist between physical and mental well-being – see "Does mental satisfaction lead to physical satisfaction?" – but I'm probably getting further afield here than you intended answers to go.

Reference
- Johnson, D. L., Wiebe, J. S., Gold, S. M., Andreasen, N. C., Hichwa, R. D., Watkins, G. L., & Ponto, L. L. B. (1999). Cerebral blood flow and personality: A positron emission tomography study. American Journal of Psychiatry, 156(2), 252–257. Retrieved from http://journals.psychiatryonline.org/article.aspx?articleid=173270.

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More to come soon from my lecture on biopsych for my class on personality a few years ago...Just a little short on time at the moment. –  Nick Stauner Apr 2 at 15:02
    

Personality studies are typically investigated via the "big five" traits. Some attempts to legitimize the personality traits through biology have been pursued [1]. Following are some excerpts from a particular study that proposed a hypothesis and searched for confirmation in 116 subjects. Of course, this means we should be wary of confirmation bias when interpreting the results. Interestingly another investigation framed the question as "personality influences on brain reactivity" [2]. I personally find this backwards. I think personality is an ermegent property of brain (coupled with environmental influences and social roles, of course).

The authors predict mechanisms for personality traits depend on sensitivity and efficiency of processing circuits. So, for instance, someone may be more neurotic because their circuits that detect dangers and threats have a lower threshold for detection.

Detection threshold play an important role because no detection system is perfect; for a sufficiently complex detection process, you have to set your threshold to bias either towards false positive or false negatives. If you were in the military or medical profession, you'd likely want to to learn more towards false negatives because you'd rather spend time on an innocent/benign than let a guilty/malignant through. Whereas, if your in business and going for efficiency, you might lean towards false positives and go ahead and sell the customer malfunctioning goods and hope only half of them want a return (as long as your customer isn't military or medical).

So a neurotic person could be said to have a detection system that leans further towards false positives than the "neurotypical" person.

Extraversion was associated with the volume of medial orbitofrontal cortex. This region is involved in coding the reward values of stimuli, and has therefore been hypothesized to be a substrate of Extraversion (Depue & Collins, 1999), which appears to reflect sensitivity to reward. Increased volume of orbitofrontal cortex has been associated with Extraversion in two other studies (Omura, Constable, & Canli, 2005; Rauch et al., 2005), and our study provides further evidence for this association.

Neuroticism was associated with reduced volume in dorsomedial PFC and a segment of left medial temporal lobe including posterior hippocampus, and with increased volume in the mid-cingulate gyrus, including both gray and white matter. These associations are consistent with the theory that Neuroticism represents the primary manifestation in personality of sensitivity to threat and punishment, encompassing traits that involve negative emotion and emotional dysregulation.

Agreeableness was associated with reduced volume in posterior left superior temporal sulcus and with increased volume in posterior cingulate cortex. The superior temporal sulcus is involved in the interpretation of other individuals’ actions and intentions on the basis of biological motion (Pelphrey & Morris, 2006), a process that may be more efficient in individuals who score higher in Agreeableness.

Conscientiousness was associated positively with volume of the middle frontal gyrus in left lateral PFC. The region of association was large, stretching from close to the frontal pole to the posterior region of lateral PFC. The middle frontal gyrus is crucially involved in maintaining information in working memory and in the execution of planned action. In terms of brain function, moving from posterior to anterior regions of lateral PFC appears to entail an increasing hierarchy of abstraction and complexity, in terms of rules that are maintained and selected to guide behavior

We found no associations with Openness/Intellect in regions large enough to be significant at p < .05, corrected. However, we did find that Openness/Intellect was associated—at p < .01, uncorrected—with one region consistent with our hypotheses: an area of parietal cortex involved in working memory and the control of attention. A previous study found that a nearly identical region (Talairach coordinates: 46, −33, 45) showed the strongest correlation between neural activity (during a difficult working memory task) and intelligence (J.R. Gray et al., 2003). This finding is significant because Openness/Intellect is the only Big Five trait that has been consistently and positively associated with intelligence (DeYoung et al., 2005)

Reference

[1] DeYoung, C. G., Hirsh, J. B., Shane, M. S., Papademetris, X., Rajeevan, N., & Gray, J. R. (2010). Testing predictions from personality neuroscience brain structure and the big five. Psychological Science, 21(6), 820-828.

[2] Canli, T., Zhao, Z., Desmond, J. E., Kang, E., Gross, J., & Gabrieli, J. D. (2001). An fMRI study of personality influences on brain reactivity to emotional stimuli. Behavioral neuroscience, 115(1), 33.

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What does "volume" signify? Other than volume, these studies show only where a trait is encoded, but not how, if I understand them correctly. –  what Apr 4 at 5:24
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How is still a matter of hypotheses. The authors introduce hypotheses in the beginning, but also reference literature (such as Depue & Collins). Encoded is probably not the right word though; "encoded" is used to describe lower processes like sensory processing well (rate coding, for example) but personality is more of an emergent property. –  Keegan Keplinger Apr 4 at 11:17
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I've updated the answer with more detail as to how the authors are explaining the how. –  Keegan Keplinger Apr 4 at 16:23

On a totally personal basis..

I know music stimulates the brain drastically. I've noticed those that seem to love learning tend to lean more toward Classic music or Techno... (that's a totally biased opinion though)

On a researching note..

http://en.wikipedia.org/wiki/Biological_basis_of_personality

The above link should be a great start for you!

The biological basis of personality is the theory that personality is influenced by the biology of the brain. Though closely related to personality psychology, the biological basis of personality focuses on why or how personality traits manifest through biology, in addition to identifying personality traits. This is investigated by correlating personality traits with scientific data from experimental methods such as brain imaging and molecular genetics.

I have been researching ways to decrease latent inhibition and the answer seems to be to increase certain chemical levels in the brain such as Dopamine.. but the down side is the increased chance of becoming Schizophrenic...

But as far as the optimism thing goes, increasing Serotonin levels might be the way to go..

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2077351/

The above is a helpful article on how to increase the Serotonin levels in your brain without the use of drugs.

Lower platelet serotonin receptor function was associated with lower mood in one study, whereas better mood was associated with higher blood serotonin levels in another. Two studies found that greater prolactin release in response to fenfluramine was associated with more positive mood.

Hope this helps and good luck with your research!!

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