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Archive for the tag “personality”

The Parasite That Changes Your Personality

Image from Wikimedia

Meet toxoplasma gondii. This lovely looking fellow is a parasite who finds host in cats, however it is also found – in the asexual stage of it’s life cycle – in other warm blooded animals, most commonly rodents but also birds and – you guessed it – humans. Luckily the parasite is kept in it’s latency stage by the human immune system, although if you have a compromised immune system it can raise it’s ugly head a little. But for the majority of people infected with this parasite, they have absolutely no idea they have a stowaway in their body. Which is quite lucky really, since about 22%-84% (Desmonts, 1974) of the worlds population is thought to carry this beastie!

The lifecycle of toxoplasma gondii, in a nutshell, goes something like: Infected rodent is eaten by a cat > parasite reproduces in the cat > parasite excreted through the feces > infects another warm blooded animal, like a rodent > form cysts in the brain, heart, and other tissue > repeat. This is why pregnant women are told to keep away from cat litter trays – because the parasite can be passed on in-utero and would certainly do a baby some damage! Even if you are not a cat owner, do not consider yourself safe. It can be ingested from unwashed vegetables for example, since the oocysts that exist in cat faeces are as persistent as a two year old with an ice-cream van outside: “These oocysts contaminate the surrounding environment; a 20-g cat stool can contain between 2 and 20 million oocysts, and after faecal decomposition, the local soil contamination can be as high as 100 000 oocysts/g and remain infectious for more than 1 year”  (Webster, 2001). Also a study of meat samples in shops in the UK found up to 38% were infected with T. gondii! (Aspinall et al., 2002)

Image from Wikimedia

That’s creepy enough. Things got interesting, however, when it was discovered that this parasite actually changes the behaviour of rodents to make it more likely that they will get eaten by a cat, thus allowing the parasite to complete it’s lifecycle. Specifically it was found that rats infected with the parasite did not show the usual fear-reaction and aversion to the smell of cat urine and in some instances even seemed to be attracted to it! (Webster, 2001;  2007) Other studies have also show infected rats to have diminished memory and maze-learning abilities, were more active, spent less time grooming before exploring new environments, and “laboratory mice…have been observed to run in circles and have their heads bent to one side.” (Webster, 2007)

This then raised the question – if this parasite can do this to rodents, does it affect humans too? Well according the the research, yes. Take this rather bold statement for example:

“Previously it was thought to be completely harmless, but the parasite actually changes your personality. If you are infected, you become more daring and unconcentrated, for example it has been noted that people that have the infection, more often are involved in traffic accidents, and even is thought be make a person suffer from schizophrenia.”
(Bech-Neilsen, 2012)

Cats really can drive you mad!
Image from: SXC

While I suspect this statement is somewhat hyperbolic considering the studies into personality changes have only shown subtle (although statistically significant) differences, and the link to schizophrenia is not nearly as clear cut as seems to be suggest here, the quote makes the point well: Your personality, and your behaviour, may be being altered by a parasite in your body.

I’ll say that again. You may have a parasite in your body (22%-84%, remember?). This parasite may be affecting the way that you think and behave without you even realising it.

Scared yet? I am!

In a correlational study looking at on a number of personality trait studies performed using Cattell’s 16PF personality trait questionnaire, a correlation between was found between infection and lower superego strength  and higher vigilance in men, leading to increased tendency to boredom, jealousy, suspiciousness, and temper in men as well as a disregard for social rules. Women, in contrast, were shown to have higher superego strength and higher warmth ratings, “suggesting that they were more warm hearted, outgoing, conscientious, persistent, and moralistic.” It has also been said to be linked to higher anxiety levels in both genders. Concentration and psychomotor skills deficits were also reported (Flegr, 2007). T. Gondii has been claimed to be responsible for 9% of intellectual disability cases in some regions. (da Silva and Langoni, 2007)

Things get really interesting when you look at T. Gondii with mental health. The link between the parasite and schizophrenia has been considered for over 50 years now, and studies have shown that individuals with schizophrenia have increased amount of T. Gondii antibodies, as well as identifying exposure to cats in childhood as a risk factor for schizophrenia (Torrey, 2003). Moreover, it has been found that many antipsychotic drugs used in the treatment of schizophrenia actually stop reproduction of the parasite in laboratory cultures. This has brought up the hypothesis that many anti-psychotic and mood-stabilising medication may work, wholly or partly, by inhibiting the T. Gondii parasite, giving support to the idea that the parasite may play a role in development of schizophrenia. To test this, a study was carried out where infected rats were treated with antipsychotic medications or water. The control (water medicated) rats exhibited the suicidal attraction to cats and other modified behaviours as described above, however the rats treated with antipsychotics did not exhibit these changes (Webster, 2007).

It’s all pretty interesting food for thought, and one thing is for sure: I’m steering clear of cats and I’m making sure my salads are very thoroughly washed from now on. Although the odds say that I’m probably already infected.If that is the case…I wonder how different I would be as a person if I wasn’t?

(References at bottom of post)


Aspinall, TV., Marlee, D., Hyde, JE., Sims, PFG., 2002. Prevalence of Toxoplasma gondii in commercial meat products as moni- tored by polymerase chain reaction—food for thought? Int J Epidemiol. 32:1193–1199.

Bech-Nielsen, S., 2012. Toxoplasma gondii associated behavioural changes in mice, rats and humans: evidence from current research. Preventive veterinary medicine, 103(1), pp.78-9.

da Silva, R.C. & Langoni, H., 2009. Toxoplasma gondii: host-parasite interaction and behavior manipulation. Parasitology research, 105(4), pp.893-8.

Desmonts G., Couvreur J., 1974. Congenital toxoplasmosis. A prospective study of 378 pregnancies, N. Engl. J. Med. 290, pp.1110–1116

Flegr, J., 2007. Effects of toxoplasma on human behavior. Schizophrenia bulletin, 33(3), pp.757-60.

Torrey, E., 2003. Toxoplasma gondii and schizophrenia. Emerging infectious diseases, 9(11), pp.1375-1380.

Webster, J.P., 2001. Rats, cats, people and parasites: the impact of latent toxoplasmosis on behaviour. Microbes and infection / Institut Pasteur, 3(12), pp.1037-45.

Webster, J.P., 2007. The effect of Toxoplasma gondii on animal behavior: playing cat and mouse. Schizophrenia bulletin, 33(3), pp.752-6.

Personality Traits

We’ve all heard of “personality types” and “personality traits”, many of us have heard of the Big Five personality traits (openness, conscientiousness, extraversion, agreeableness, and neuroticism) and many of us have taken personality tests on facebook, websites and so on. Such tests range from the mildy amusing to the scientifically supported and thorough. But what does it all mean, and where did it all come from?

Something I love with studying psychology is looking at how theories have developed, how theorists have worked together, against each other, and even occasionally stolen ideas or had big arguments. I love tracing the evolution of our modern understanding through time, and looking at Trait Theory of personality psychology is a great example of that.

What are Personality Traits?

Trait theories of personality describe individuals personality and behaviour as driven by underlying dispositions or traits that are bipolar in nature (have two opposites, e.g. introvert/extravert), and consistent and stable over time. Individuals are said to have different combinations of traits, or strengths of those traits.

The trait theory of personality goes back as far as the likes of Aristotle and Hippocrates.

Francis Galton

Francis Galton (Photo credit: Wikipedia)

Sir Francis Galton (1884)

Although the factor analysis approach to personality traits is sometimes credited as starting with Allport and Odbert’s (1936) work, it actually goes back almost a century before that to Francis Galton (1884). Galton made the first investigations into what has become known as the lexical hypothesis – the idea that

  1. Important individual differences in personality will become encoded in the language of the culture
  2. The more important that difference is, the more likely it is to be captured in a single word

“I tried to gain an idea of the number of the more conspicuous aspects of the character by counting in an appropriate dictionary the words used to express them…”

—Francis Galton, Measurement of Character, 1884

Gordon Allport

Gordon Allport, American psychologist. (Photo credit: Wikipedia)

Allport and Odbert (1936)

Allport and Odberd went through Webster’s New International Dictionary and picked out just under 18,000 words that they believed to describe personality and mental states. From this they around 4,500 selected words which fit their definition of traits as “generalized and personalized
determining tendencies—consistent and stable modes of an individual’s adjustment to his environment”.

Allport also split traits into three categories:

  1. Cardinal Traits – those traits that are core to the way a person behaves, the most defining traits of a certain individual
  2. Central Traits – those traits that are found in everyone and shape and influence the way we behave, but not in the overriding manner of cardinal traits
  3. Secondary Traits – traits that are only exhibited in certain circumstances or situations

This alphabetised trait list was provided as a resource for other psychologists…

, British-American psychologist

Raymond Cattell (Photo credit: Wikipedia)

Raymond Cattell (1943, 1957)

Cattell (1943) started with Allport’s trait list, however he felt it was insufficient and added to it “the substance of all syndromes and types which psychologists have observed and described in the past century or so” (Cattell, 1943 as cited in Block, 1995). Based on his own understanding and decisions Cattell organised the list into 161 trait “clusters” (largely by dropping synonyms and combining synonym/antonym pairs into a single measure), to which he added a further 21 based on his readings of intelligence and values, and at some point he must have also dropped some to end at 171 – however how this came about was not documented.

Factor Analysis Aside

Factor analysis looks at the correlations between variables and attempts to identify underlying elements called factors. For example Charles Spearman, credited with the invention of factor analysis, found that children’s performance in a variety of unrelated subjects seemed to be correlated, which led him to the conclusion that an underlying mental ability drove performance in all those areas. This was the start of intelligence research!

Next Cattell asked two colleagues to rate 100 target persons on the 171 clusters of trait terms, which aquaintances of the target persons were also asked to do. Analysing the correlations (a set of 14,535 correlations laid out on 14 square feet of paper) Cattell identified around 67 ’empirical’ clusters of traits. Based on this, combined with analysis of twelve other ratings studies, he drilled down further to 35 clusters. Finally with these 35 traits a number of ratings studies were carried out similar to the first one, which, using factor analysis, led him to 12 factors, which are the foundation of his Sixteen Personality Factors Questionnaire (16PF) (the remaining four being specific to the self-rating model of questionnaires). Those sixteen traits are:

Warmth, Reasoning, Emotional Stability, Dominance, Liveliness, Rule-Consciousness, Social Boldness, Sensitivity, Vigilance, Abstractedness, Privateness, Apprehension, Openness to Change, Self-Reliance, Perfectionism, Tension

You can take a version of the 16PF online free, although I cannot vouch for its accuracy.

And if you thought that was complicated, you should read the full story! (See: John & Angleitner, 1988).
five second order or global factors

In later work Cattell factor-analysed the 16 traits and found five global or “second order” categories, which can be likened to the Big Five Personality Traits that are popular today.

As an aside, Cattell, like Galton before him and Eysenck after him, believed in the inheritability of traits (that personality traits were passed genetically from one generation to the next), and was an active supporter of Eugenics – which caused controversy for all of them and lead to Cattell missing out on a lifetime achievement Gold Medal Award from the American Psychological Foundation (part of the APA).

Raymond Christal

Raymond Christal

Ernest Tupes and Raymond Christal (1961, 1992)

Despite Cattell’s overlooked five second-order factors, Tupes and Christal are credited with the “discovery” of the Big Five personality traits. Using factor analyses on various samples, five strong dimensions kept appearing:

Surgency, Agreeableness, Dependability, Emotional Stability, Culture.

Cattell saw this as an attack on his Sixteen Personality Factor model, and openly criticised “the five factor heresy”.

Tupes and Christal’s work, partly due to not being published in an archived journal for some years combined with a shift in attitude towards trait theories at the time, passed largely without major impact.

Warren Norman (1967)

Norman compiled an exhaustive list of personality descriptive terms that he considered suitably precise, well structured, and exhaustive for use in constructing personality theory. He started with Webster’s Third New International Dictionary and added 171 new terms to Allport’s list, giving a new set of 18,125 words. Norman split the words into four categories: Biophysical traits (e.g. calm, chirpy, pedantic); Temporary States and Activities (e.g. hesitant, sad, smitten, bickering); Social Roles, Relationships, and Effects (e.g. leader, droll, repellant); and Excluded Categories (evaluative terms, physical traits, ambiguous and vague terms, and obscure terms). From the almost 2,800 trait terms in the Biophysical traits category Norman was able to draw out 1,566 trait terms by analysing ratings of 100 students. He was then able to categorise these words into ten clusters, one cluster for each end of the bipolar measures of the Big Five.

Lewis Goldberg (1971)

Building on the work of Norman, Goldberg brought trait psychology back into vogue and coined the term “the Big-Five” in a 1982 paper. Goldberg worked with the lexical hypothesis and produced a list of 1,710 trait terms to use. Based on the self-ratings of 187 college students and 75 categories Goldberg had identified in his list, he extracted the now famous Big-Five traits. These same five traits appeared across a number of different analysis methods. Interestingly, however, and currently unpublished, when Goldberg rotated six or seven factors rather than five, he found that the five split out. In particular on a six-factor rotation Norman’s Factor V split into an ability factor and a culture factor; additionally in a seven-factor rotation categories related to religiosity formed a factor of their own (John & Angleitner, 1988). These findings have paralells in studies by other psychologists.

This photograph is being given to Wiipedia for...

Hans Eysenck (Photo credit: Wikipedia)

Hans Eysenck (1968)

Eysenck moved away from the lexical approach that had thus far dominated trait theory toward a questionnaire approach. This approach examines people’s responses to personality questionnaires rather than trait lists, which allows for more complex personality factors to be captured than the single words of the lexical approach.

Unlike Cattell, Eysenck viewed personality as seperate from intelligence. He also was heavily influenced by Carl Jung’s introversion / extraversion concept, however he saw them as a trait rather than a type as Jung had. Neuroticism (emotional instability) formed the second core trait of Eysenck’s trait model, and for a while these were the only two traits that Eysenck believed underpinned human personality. The Eysenck Personality Inventory (1968) reflected these two traits, however a revision of the survey entitled the Eysenck Personality Questionnaire (1975) added psychoticism as a third trait. This inclusion of psychoticism proved to be a step backwards in the theory in many ways as it wasn’t well empirically supported, particularly with creative personalities like artists and musicians scoring highly on this measure.

Eysenck tied his traits to biological sources, hypothesising that differences in extraversion were down to individual differences in the Ascending Reticular Activating System (ARAS) of the cortex, and differences in neuroticism were linked to individual differences in the limbic system. He provided some evidence for the former, but was unable to provide any for the latter. He also never tied a biological cause to his psychoticism trait, further fuelling the criticism against it’s inclusion.

Cattell and Eysenck argued publicly over the optimal number of traits that should be used in a trait theory model of personality, as did Eysenck and Costa& McCrae.

Costa & McCrae (1993)

Costa & McCrae were driven by the goal of showing that the apparently dissimilar personality schemes at the time were in fact measuring the same things, and they made large efforts to integrate their model with these other schemes.
Costa & McCrae’s model defines five personality traits that can be remembered with the acronym OCEAN:

Neuroticism (N)
Extraversion (E)
Openness (O)
Agreeableness (A)
Conscientiousness (C)

Costa & McCrae’s model formed the basis for what is now one of the most widely used measurement scales: NEO-Personality Inventory-Revised (NEO-PI-R; Costa and McCrae, 1992)

Rodin's The Thinker

Rodin's The Thinker
(Picture credit: Wikipedia)

Food For Thought

As you can see it has been a long and interesting journey in all, and there is quite a lot I have left out for my own sanity as much as yours (I only actually need to know about two of the above for my upcoming exam!). But take a moment to consider these questions:

  • Do you think Trait Theory can capture a person’s personality and predict their behaviour?
  • How useful is it to reduce behaviours and personality to these few dimensions?
  • What criticisms and weaknesses can you think of for the research and theories described above?
  • Should someone’s beliefs in one area (e.g. eugenics) shadow their achievements in another (e.g. trait theory)?

Have a think, and leave a comment!


Block, J., 1995. A contrarian view of the five-factor approach to personality description. Psychological bulletin, 117(2), pp.187-215.

Costa & McCrae, 1992, NEO PI-R Professional Manual. Odessa, FL: Psychological Assessment

John, O. & Angleitner, A., 1988. The lexical approach to personality: A historical review of trait taxonomic research. journal of Personality.

Life Goal

I have been thinking recently about my life, about the choices I make, about the things I do. This has raised the question in my mind: why?

What exactly am I aiming at, what do I want from life? I know I want to help others, that I want to be some kind of therapist, but again I ask myself why. What makes me want to help others so much? Is there something, some goal that when I reach it I Will feel fulfilled? Some psychologists believe that all our behaviour is driven by a core desire; to be famous, to be loved, to be rich, to have big family, that kind of thing.

It is important to have goals to drive you forward. Having a definite goal is especially important when working on a degree because it is what will motivate you to work harder, to get that good grade you know deep down you can. But if you want to be a therapist you have to look deeply at exactly *why* you are doing it. Because your motivations, whether you are consciously aware of them or not, can have an affect on the therapy you provide for your clients. One example motivation is to become a ‘rescuer’, playing out anxieties from childhood where you have lost someone close to you. This can be very damaging for the client as it forces them into the ‘victim’ role. But if you are aware of it you can manage it and prevent it from interfering.

Heck, I have even heard anecdotally that some training therapists have abandoned their new career completely once they uncovered what was motivating them.

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