Sensory Integration in the Whisker Pathway

Posted on Updated on


This was the last major assignment I had to do for my bachelor’s degree and I received a HD! It is an annotated bibliography (11 papers) with a short summary:


The reading topic to be covered in this assignment was “sensory integration in the whisker pathway”. This encompasses how information from the sensory system is translated into neural correlates that can be understood by the brain, and how the cortical representation of these sensory inputs can generate a behavioural response. The main model of choice is the rat whisker-barrel system because of its functional efficiency and anatomical characteristics, as the whisker region of the primary somatosensory cortex have clusters of neurons called “barrels”, each of which correspond primarily with one whisker [1]. The applicability to humans has been compared to the way people use their fingers to sense tactile information at times [2], although there are obviously many differences in terms of the function and sensorimotor feedback mechanisms used in fingertips that are not used in whiskers.

There are three main parts to sensory integration in the whisker pathway. First, it is important to know how the sensory input is translated into spikes, or neural coding. Secondly, it is important to understand how this is correlated to activity in higher cognitive areas, such as the somatosensory cortex. Finally, the correlation between neuronal activity and behavioural response to the stimulus is essential to know in order to understand the effects of sensory integration.

Rat whiskers (mystacial vibrissae) have many sensory receptors on them (in the follicle), innervated by hundreds of primary afferent fibres, and the signals generated by these have been correlated to anatomical and functional maps in the cortex [3]. The motion of the whiskers move the follicles, and the sensory receptors, which are the terminals of trigeminal cells, create action potential trains [4]. The neurons respond differently to different stimuli based on features such as speed of adaptation, location, direction, and velocity of whisker displacement, whisking phase, and contact or detachment [5]. The whiskers can be used to perceive space in three dimensions and identify the shape of objects, and can thereby categorise responses into ‘what’ and ‘where’ systems [6]. The whisker response can also be affected by the mode of sensing; rats can still their whiskers (receptive) or whisk them (generative) to get different information on their surroundings [5].

Once the mechanical information has been translated to spikes, they travel through the parallel pathways and the thalamus to the primary somatosensory cortex areas corresponding to the whisker, or the barrel cortex. It has been shown that a general linear model can be applied to the primary afferent response to sensory signals [7]. The features of whisker motion that the sensory system uses to construct sensations was found to be the product of both amplitude and frequency (Af), which means the speed of the whisker is required to perceive sensations [8]. Whisker movement seems to be initiated by the motor cortex (protraction) and the somatosensory cortex (retraction), which shows that sensory integration plays a role in generating movement independent of the motor system [9]. However, another paper suggests that the somatosensory information is relayed to the motor cortex, which correlates with whisker movement and so helps with ongoing sensory perception, especially in relation to fine adjustment of individual whisker movement [10]. The role of the motor cortex is called in to question in another paper, which states that although it has a role, it is not responsible for signalling the sensory cortex about the whisker position during whisking [11]. The same article does establish that spiking pattern can be generated by whisker motion. Most researchers call for more studies to be done, especially on active behaving rats instead of anaesthetised ones.

Annotated Bibliography

1. Adibi M, Arabzadeh E. A Comparison of Neuronal and Behavioral Detection and Discrimination Performances in Rat Whisker System; 2011:356-365.
Research Notes: The aim of this study was to understand the correlation between cortical neuron response and rat behaviour. Rats were anaesthetised so that neuronal activity could be recorded in the somatosensory cortex while vibrotactile stimuli was applied to the whiskers. The single neurons were measured for detection and discrimination. Rats were then trained to distinguish between two vibrations, and it was found that they were better at discriminating than detecting in both behavioural and neuronal response measurements. Faster whisking means higher firing rate. The brain activity was measured while the rats were anaesthetised, and perhaps that might change the data, and it is mentioned that there was no whisking in the anaesthetised condition. The paper is useful in understanding the connection between sensory experience, brain activity, and behaviour by measuring the neuronal and the behavioural responses. It shows that there are correlations between sensory integration and neuronal and behavioural responses.

2. Fassihi A, Akrami A, Esmaeili V, Diamond ME. Tactile perception and working memory in rats and humans. Proceedings of the National Academy of Sciences 2014;111:2331-2336.
Research Notes: Compares efficacy of working memory in rats (and their use of whiskers) and humans (and their use of fingertips) in sensory discrimination. Shows rodents have more capabilities than previously expected. Helpful in that it uses both human and rat test subjects and shows similarities between them.

3. Arabzadeh E, Heimendahl MV, Diamond M. Vibrissal texture decoding. Scholarpedia 2009;4.
Research Notes: This webpage aims to summarise the current knowledge on the correlates between whisking and texture sensation of surfaces using the vibrissae system in rats. Vibrissal texture decoding will help investigate the signals (and their interpretation) generated by sensory receptors in response to the environment. The data was collated through many different studies. Describes the long whiskers (focus of this paper) which have correlating anatomical and functional maps. Describes the thresholds of texture differentiation and duration required to make a decision. Concludes that the kinetic signature hypothesis for encoding texture is the most plausible one so far, but there are still missing pieces. The neuronal firing rate-to-whisker kinetics relation was outlined in anaesthetised mice, but not in alert ones. The paper outlines plausible read-out mechanisms (from spike train to discrimination behaviour) and further investigation in other areas such as sensorimotor integration. This chapter is useful as a clear summary of the research, and is written simply and without too much jargon or methodology.

4. Diamond ME, Arabzadeh E. Whisker sensory system – From receptor to decision. Progress in Neurobiology 2013;103:28-40.
Research Notes: This paper’s goal was to characterise the behaviour of the rats’ whiskers, their specific motions in response to the external stimulus, the translation of stimulus to neural coding in the sensory cortex, and what happens afterwards. It’s long-term goal was to study the pathway between stimulus and receptor to decision and behaviour. This was done using a number of different research methods, including prior research analysis and some extrapolation, electrical stimulation, the creation of a texture library which profiled whisker movements per texture, measurement of kinetic signature, recording of responses in first-order, recording cortical activity at the same time as whisker behaviour using a high speed cameras, and training rats in behaviour paradigms to discriminate between textures in both generative and receptive conditions. The article is useful as it gives a comprehensive outline of what has been found and what needs to be studied. It is mentioned that the whisker-barrel system is used as it is an expert sensory system with direct correlates between sensory input and behaviour, cortical stimulation, and resulting decision-making, and its anatomical and functional organisation is exquisite and well studied. It can therefore be used as good source material for future studies or to gain a better understanding of the research that has been done so far.

5. Maravall M, Diamond ME. Algorithms of whisker-mediated touch perception. Current Opinion in Neurobiology 2014;25:176-186.
Research Notes: This study aims to identify the computations used along the receptor-to-cortex pathway in converting physical signals to sensations. It summarises what is known about the follicles and how they respond to different stimuli, the role of the mechanoreceptors/trigeminal ganglion neurons, generative vs receptive sensing, differences in TG, VPM, and Barrel Cortex neuron firings, sparseness, response heterogeneity, spike timing, adaptation, barrel cortex population coordination, and how downstream neurons can use a simple decoding scheme using linear synaptic weighting to identify texture. The conclusion offers some experimental paradigms that could help solve some of the unanswered questions. This review is useful as it is an up-to-date collation of what is known about the first step in integration of sensory information; the translation of mechanical stimulus to cortical language. It’s a relatively short review as it covers a very specific area in detail, rather than what is known of the whole picture.

6. Diamond ME, von Heimendahl M, Knutsen PM, Kleinfeld D, Ahissar E. ‘Where’ and ‘what’ in the whisker sensorimotor system. Nat Rev Neurosci 2008;9:601-612.
Research Notes: This study summarises the information on the whisker sensory system and looks to present evidence on how external stimuli is represented in the brain, an in particular the “what” and “where” systems. Used behavioural studies on wake animals and recorded sensory receptor neurons in anaesthetised animals (artificially stimulated whiskers) and found that rats use their whiskers to perceive space in three dimensions, there may be three functional classes of primary sensory neurons (‘where’), and whiskers can identify the shape and texture of objects. The paper ended with an outline of two possibilities for the sensory system’s knowledge of the behaviour response, and then future research directions. The paper is useful in that it divides the different courses of information into two streams that can be looked at separately. Sensory integration in the whisker pathway is looked at in a broader sense, and more studies can be built upon the collated information.

7. Bale MR, Davies K, Freeman OJ, Ince RA, Petersen RS. Low-dimensional sensory feature representation by trigeminal primary afferents. The Journal of Neuroscience 2013;33:12003-12012.
Research Notes: The study aims to create a model to predict the primary afferent response to sensory signals. This is based on the premise that whisking and object contact with the whisker evoke spikes, that the pattern of action potentials travel from primary afferents to the cerebral cortex through parallel, trisynaptic pathways, and that primary afferents respond to whisker motion with reliable spike-timing precision. Creating a model helps clarify the relationship between whisker motion and afferent response. It was found that a generalised linear model could predict the responses of the afferents in both white noise and texture-induced whisker motion. The model was rigorously tested  for and it was found that it could predict both timing and amplitude of the peaks, although it was more accurate when predicting white noise. The authors note that an even more accurate model would take in to account slow time course features of the stimulus, and that the model should be tested on behaving animals. The aspects covered by the model were stimulus filtering, spike feedback, and whisker motion and velocity. Using this model and building upon it could be useful in future studies, as well as for understanding different sensory systems. The article was useful in that it outlined and created a model for the first step of sensory integration: translating mechanical stimuli to neuronal processing.

8. Adibi M, Diamond ME, Arabzadeh E. Behavioral study of whisker-mediated vibration sensation in rats. Proceedings of the National Academy of Sciences 2012;109:971-976.
Research Notes: This paper addressed the features of whisker motion that the sensory system uses to construct sensations by training rat models to discriminate between different sinusoidal vibratory models on the left and right whiskers. The focus was on keeping the frequency (f) or the amplitude (A) equal. It was found that vibrations were sensed as a product of Af, which means the speed of the whisker is used to perceive sensations. Both single and cortical ensembles of neurons encoded the Af using firing rates. The study also showed that the rats’ judgement can be wrong if the final Af of both sides are equal, even if the separate A and f were different, which can be one reason why rats are not always correct. The study was interesting in that it used behaving rats instead of anaesthetised rats, which gave different results to prior studies. Could not tell if the paper explicitly mentioned what sort of sensory perception was being used (receptive or generative) (probably generative). This article is useful in that it looks specifically at how rats use their whiskers to discriminate between vibrations, which is a function of the first step in understanding sensory integration. The authors end the paper by saying the firing rate, and not its individual components, is the most salient property.

9. Matyas F, Sreenivasan V, Marbach F, et al. Motor control by sensory cortex. Science 2010;330:1240-1243.
Research Notes: The authors aimed to study the role of the primary somatosensory barrel cortex in controlling movement, as opposed to motor cortex control. They mapped sensory activity using one whisker for both the motor and somatosensory cortex areas, then inactivated each area to record a change in retraction response. Results implied the motor cortex is only required for protraction, not retraction, and these two pathways used different routes in the brain stem to get to the whiskers. They posed the question of whether sensory cortex motor control is apparent in just the whisker system or whether it can be generalised. The article relates to the end product of sensory integration – behavioural response.

10. Ferezou I, Haiss F, Gentet LJ, Aronoff R, Weber B, Petersen CCH. Spatiotemporal Dynamics of Cortical Sensorimotor Integration in Behaving Mice. Neuron 2007;56:907-923.
Research Notes: The paper shows the involvement of the motor cortex in sensory perception through a feedback loop of sorts. This view seems to be different from views in other papers, which generally focus on other parts in the sensory integration of information gained through the whiskers. The study uses voltage-sensitive dye to image the interactions between somatosensory and motor cortexes. It concludes that information from a single whisker deflection goes to the somatosensory cortex, is then relayed to the motor cortex, which then correlates with whisker movement, and so helps in ongoing tactile sensory perception. The motor cortex may use sensory input to affect fine adjustment of individual whisker movements. Authors mentioned problems in imaging technique; change in membrane potential does not necessarily mean action potentials were produced, so sensory response may be less distributed than the study suggests. However, they believe this form of imaging is promising for future endeavours. The paper shows how sensory information may  be used as it is being integrated.

11. Fee MS, Mitra PP, Kleinfeld D. Central Versus Peripheral Determinants of Patterned Spike Activity in Rat Vibrissa Cortex During Whisking; 1997:1144-1149.
Research Notes: The researchers address the sources of input for the rat whisker-barrel cortex by recording single unit spike trains during whisking. They found that whisking occurs independently from sensory feedback and single neuron output may represent whisker position. The study concludes that it is not the motor cortex which plays the main role in signalling the sensory cortex about the position of the whisker during whisking, and that the spiking pattern comes from whisker motion. The article is useful in establishing a basis for the correlation between movement of the vibrissae and neuron activity in the primary somatosensory vibrissa cortex, and in giving some insight as to what the corollary discharge might be doing. Further research is required. The paper is a bit old and does not use terminology such as whisker-barrel system, etc.

Thinking in Another Language

Posted on Updated on


There is this phenomenon I may have talked about before, where people who speak different languages also tend to think is different ways. I’ve watched documentaries on this and I may have even studied this at some point. Perhaps due to culture, perhaps due to the way the language is structured, either way, it is quite easy to notice that people who grow up speaking a different language will probably also have a different thinking pattern to you.

An example from a documentary (from what I recall, since I cannot seem to find this documentary anywhere) is a test between Japanese and English native speakers. They showed a picture of a group of people with certain expressions. On some, the main person had a happy face while the others all had sad faces. When asked to say what the person in the middle was feeling, the English speakers said he was happy, whereas the Japanese speakers said he was sad, despite the happy face, because the people around him were sad.

Of course, this could be due to the social environment Japanese and English native speakers grow up in, rather than the language they speak. Another example of how language affects our perception is our ability to see colour. Basically, if your language doesn’t have a word for a certain shade, it’s unlikely that you can see it (article). Here’s another study that tests bilingual people using colour perception.

If something as ‘physical’ or ‘biological’ as vision is influenced by our language, what else is?

I bring this up now because this is knowledge I had learned before but had stored away in some unimportant storage compartment in my brain. Like most psych facts you learn as a teenager, it seems really cool but it is rarely put in to practice.

Until yesterday.

I never thought I had any good ideas for stories, especially for Uyghur related things. What I had never actually tried was to write a story in Uyghurche. Isn’t that weird? I don’t actually recall ever writing a story in Uyghur.

So when I started writing on a whim, suddenly I had all these great ideas for a story! Where were all these coming from? Is it really because I was thinking in a different language? I usually think in English. I didn’t think that when I wrote in Uyghurche, the half formed sentences or ideas in my head would crystallise. I had grown up listening to so many Uyghur stories from my uncles. Did thinking in Uyghurche exhume all those forgotten memories, feelings, and ideas?

I always rant about points of views and how important it is to step in to other people’s shoes and actually think from their perspective but I’d some how forgotten that there was a whole new way to do that, and it was through an Uyghur speaking mind.

Yet another advantage of being bilingual!


2017 Edit: I just found an article that says language influences how we perceive time as well

On Agar Cultures

Posted on Updated on


In class today we were told how scientists around 200 years ago figured out that plating cultures on agar was the best way to go.

They had wanted to use gelatin, except sometimes you need to grow things at body temperature and gelatin is almost liquid at that point, which isn’t ideal for cultures. The scientist returns home one day and talks to his wife about his work and the problems he was facing. So the wife suggests, why not agar? Germans apparently used it to harden jam and the like. He took that on board decided to try it. The next day he went to work and BAM – instant success. And we have been using agar ever since. For almost 200 years.

So yes, fresh eyes and a different sort of knowledge really does help. Science requires knowledge of all sorts of stuff. Everything is science. Keeping science to just reasonably privileged males does not do anyone any good, not even them. More women in science, more artists in science, more philosophers – science needs to be open and accessible to everyone for it to affect change on society. The more minds involved, the faster we go.

Why Do You Get Thirsty?

Posted on Updated on


…because there is an increase plasma osmolality or a decrease in plasma volume.

Taking up extra salt decreases blood volume as more water is pulled out from the surrounding fluid (because salt is in the extracellular fluid and is increasing osmolality), and arterial pressure increases. When arterial pressure increases, more fluid with more Na+ passes through the macula densa. Macula densa senses the high amount of salt and releases a signal to decrease renin and so decrease angiotensin. Angiotensin is responsible for the release of aldosterone, which is meant to be the salt saving hormone. Therefore, less salt is saved, and more of it leaves the body. Water follows the salt along osmotically, so you become thirsty.

If you increase your protein intake by a lot, the increased amount of nitrogen you consume could mess up the macula densa system.

Another way you become thirsty is by lowering water intake (dehydration). Since there is increased extracellular osmolality, the brain recognises this and sends over ADH (antidiuretic hormone), which binds to the blood side of the collecting duct (in the nephrons of the kidney). This increases water reabsorbtion (water —> interstitial space —> vasa recta —> blood stream), and less water is excreted.

The Dark Triad of Personality

Posted on Updated on


This is an essay I wrote for first year psychology at uni. It argues that the components of the ‘Dark Triad’ (narcissism, Machiavellianism, psychopathy) should be evaluated separately because they are separate things. I haven’t edited it since I’ve gotten it back from my tutor, so this is basically what a Distinction essay looks like at my 1st year uni psyc course (the highest mark being High Distinction).

The Dark Triad of personality has seen an increase in interest recently and many have looked for ways to quantify or measure it. According to Paulhus and Williams (2002), the Dark Triad consists of narcissism, Machiavellianism, and psychopathy. In order to accurately measure the Dark Triad, one needs to be able to distinguish whether these three constructs are in fact distinct or equivalent. This essay will argue that the three are closely related but dissimilar personality traits. Seminal research is looked at in order to define the three parts.

Narcissism was typified by Kernberg (1975) as relating to someone who is grandiose, extremely egoistical, and has low empathy despite needing to be liked by others (p. 228). Object-relations, which is the way in which the self externalises or internalises other people or objects (Greenberg & Mitchell, 1983. p. 13-14) is an important element of narcissism (Kernberg, 1975). Narcissists need to have continual reinforcement for their egos (Kohut, 1951), and with the reinforcement feel that they are superior and so permitted to exploit others because they are entitled to do so (Kernberg, 1975). Narcissists can be manipulative, and will do anything to fortify their identity (Paulhus & Jones, 2011). There is also a subclinical form of narcissism that can be measured with Raskin and Hall’s Narcissistic Personality Inventory (NPI) (1979) which still preserves such components of narcissism as “grandiosity, entitlement, dominance, and superiority” (Paulhus & Williams, 2002, p. 557).

Machiavellianism was a term based on the book The Prince by Niccolo Machiavelli of 16th century Italy by Richard Christie (Christie & Geis, 1970). A person with this trait tends to be very manipulative and focused on achieving long term goals through any means, and is an individual with a good command of impulsivity (c.f. Jonason & Tost, 2010) and is well adaptable (Christie & Geis, 1970). Christie also developed a way to measure this trait with a test called the Mach IV. Further studies added coldness and a lack of sincerity and care to the typical Machiavellian personality (Jakobwitz & Egan, 2006).

Psychopaths, according to Cleckley (1976) have inconsistent, impulsive behaviour and are inclined to take action with disregard for reputation, regret, or consequence. They seem to have no disposition to forming long term goals because of these factors (Jones & Paulhus, 2011). Subclinical psychopathy was defined by Hare (1985) who created the SRP (Self Report Psychopathy) and the SRP II (Hare, Harpur, & Hemphil, 1989) to measure degrees of psychopathy in normal populations. This could predict whether the person was more likely to cheat, or be violent, anti-social, thrill seeking or a delinquent (Paulhus & Williams, 2002).

There are similarities between these three traits that some would reason is sufficient to say they’re equivalent. However, this paper will argue that the differences can adequately distinguish each from the other based on the Big Five, traits such as aggression, mating methods and societal advantages, as well as genetics and sex differences.

The Big Five is often used to compare the relationship between narcissism, Machiavellianism and psychopathy. It has been shown that they all share a consistent low in agreeableness (Paulhus & Williams, 2002; Miller & Campbell, 2008). However, it has been argued that there can be different types of disagreeableness, stemming from different types of conflicts (Miller, Dir, Gentile, Wilson, Pryor, Campbell, 2010). So despite the apparent similarity between the three, a deeper look demonstrates the inadequacy in deeming each the same because of this correlation.

According to Paulhus and Williams (2002), psychopathy and Machiavellianism shared low conscientiousness, and psychopathy and narcissism shared higher extraversion and openness. These results favour some researchers’ claims that the factors in the Dark Triad are equivalent. For example, Machiavellianism and sub-clinical psychopathy was shown to be interchangeable since sub-clinical psychopathy could be detected using the Mach IV in normal populations (McHoskey, William, Christopher, 1998). Gustafson & Ritzer (1995) showed that there is a significant overlap between sub-clinical psychopathy and narcissism and used them somewhat interchangeably in their study of ‘aberrant self-promoters’ (the same study regarded Machiavellianism as too different to put under the same heading). Both these correlations were supported by a genetics study done by Vernon, Villani, Vickers & Harris (2007) who also reported no correlations between Machiavellianism and narcissism. But the latter result is not consistent with studies done by Paulhus & Williams (2002) and Jakobwitz & Egan (2006) who say that there is still a small correlation between narcissism and Machiavellianism. Nevertheless, the similarities based on the Big Five can be looked over as there are differences between the three that make it harder to establish all as identical structures. For example, in the same Paulhus and Williams study, neuroticism was only seen to negatively correlate with psychopathy, therefore distinguishing psychopathy from both narcissism and Machiavellianism. Only narcissism had a higher level of conscientiousness, and only Machiavellianism had a negative correlation with openness. Due to these findings, an argument claiming that these constructs are equivalent cannot be made based on the Big Five alone.

Another distinguishing feature is aggressiveness. It is widely agreed upon that psychopaths are prone to be aggressive and impulsive (Jones & Paulhus, 2010; Jonason & Webster, 2010; Gustafson & Ritzer, 1995; Cleckley, 1976). Machiavellianism has some divided literature, some saying that they could employ the use of aggression to achieve their aims (Jonason & Webster, 2010) whereas others find that Machiavellians tend not to overtly display any aggression they might feel (Lau, 2010; Jones & Paulhus, 2011). Machiavellianism has been shown to correlate negatively with impulsiveness (Gupta, 1991), which is the opposite of the definition of psychopathy. The varying results in aggressiveness imply a definitive difference between psychopathy and Machiavellianism. Narcissists were shown to be hostile but not aggressive in some studies (Jonason & Webster, 2010) but in others were shown to be highly aggressive, especially when their ego was threatened (Bushman & Baumeister, 1998; Bettencourt, Talley, Benjamin, & Valentine, 2006). The differing results and lack of consensus suggest further evidence of discrepancy between the three constructs.

A similarity within the Dark Triad is that despite generally being negatively viewed by society, they may have some adaptive advantages in regards to mating strategies and psychological health. However, the way in which each of the three pillars contributes to being an advantage is different.

In mating strategies, the Dark Triad has been linked to short term mating and having more sexual partners (Jonason, Li, Webster, & Schmitt, 2009; Jonason, Li, & Buss, 2010) which is beneficial to them in that their genetics will be continued, and certain traits aren’t discontinued due to sexual selection. The difference is in the how. Short term mating in narcissists seems to have come about because narcissists have a positive correlation with attractiveness (c.f. Gabriel, Critelli & Ee, 1994) and the traits required to not form attachments to their mates (Holtzman & Strube, 2010). Psychopaths, on the other hand, seem to have developed short-term mating strategies due to their general deceptiveness and duplicity (Seto, Khattar, Lalumière, & Quinsey, 1997) and probably because of their impulsiveness and overall lack of empathy or anxiety. According to Jonason, Luevano and Adams’ (2012) study of different types of short-term mating strategies, narcissists were open to many types of relationships (for example, friends with benefits and one night stands) and have  tendency to score high in sociosexuality (Reis & Wright, 1996). In contrast, psychopaths were more disposed to choose exploitative relationships (Jonason et al., 2012).

In regards to psychological health, according to some (Bach, 1977; Emmon, 1987; Kohut, 1951) narcissist have a low perception of themselves and this delicateness could lead to feelings of grandiosity. However, other researchers have found that narcissist reported the same, if not a better self-view than non-narcissists and that this aspect of narcissism has psychological health benefits (Rhodewalt & Morf, 1995/2001; Sedikides, Rudich, Gregg, Kumashiro, & Rusbult, 2004). Interestingly, in a study designed to test how “darkly” people see each of the three constructs, narcissists were seen as “brighter” than the other two, with some favourable aspects denoted to them (Rauthmann & Kolar, 2012). This study hints that being at least sub-clinically narcissistic is beneficial in that with the higher self-esteem that comes with the condition, other’s perceptions become more positive as well. Nonetheless, narcissism is presented as a separate paradigm within the Dark Triad in this regard.

A Machiavellian personality can lead to good when dealing with corporations or companies, especially if the bettering of said company would be seen as a personal success, or long term goal for the Machiavellian (Christie & Geis, 1970). With subclinical psychopathy, it’s been pointed out that one could strive to achieve their goals in contrary circumstances due to their lack of anxiety (Taylor & Armor, 1996). Although the two can be seen as positive outcomes of a negative personality, the way in which each of the constructs work to gain the positive ground is dissimilar. This can be likened to convergent evolution, which is when two unrelated animals develop similar characteristics based on similar needs. For example, both birds and bats can fly despite not being genetically akin.

Recently, genetic studies have been conducted to verify differences between psychopaths, Machiavellians and narcissists. It has been concluded in a few studies that psychopathy (Larsson, Andershed, & Lichtenstein, 2006) and narcissism were heritable traits, but Machiavellianism was heritable only slightly (Vernon et al., 2008,). Machiavellianism as a learned trait is supported by research from Brumbach, Figueredo and Ellis (2009) who predicted that the dark personality could become apparent after a rough upbringing. Another study was conducted to see whether morality could be correlated with the Dark Triad and whether it had a genetic basis (Campbell, Shermer, Villani, Vickers, & Vernon, 2009). Results showed that higher scorers on psychopathy had low scores on morality and moral development. Similar results were shown for Machiavellianism, although the negative correlation between moral development and Machiavellianism was not significant. The study concluded that morality was based almost entirely on environmental factors and not genetic ones, but it is suggested that Machiavellians, unlike psychopaths, can attain a higher stage of moral reasoning and act immorally despite knowing what they do is wrong (Jones & Paulhus, 2011). Further research can be done in regards to genetic and environmental factors that link the Dark Triad traits to outward behaviour, but as of now psychopathy and narcissism seem to be separable from Machiavellianism developmental-wise, in regards to being genetic or environmentally based.

A lot of evidence points to how men often score higher in Dark Triad tests than women (Paulhus & Williams, 2002). In Machiavellianism and narcissism, the difference between sexes was shown to be very little (Jonason, et al., 2009). In contrast, the difference between males and females in levels of psychopathy was shown to be significant (Cale & Lilienfeld, 2002). However, more studies should be carried out in this area since the majority of the literature on the Dark Triad is either male oriented, or the differences in sexes aren’t the main focus.  Also, a lot of the research is done on either college students or delinquents in Western societies, despite there being evidence showing that the three traits are seen in other societies as well (Jonason, Webster, Schmitt, Li, Crysel, 2012). Perhaps further cultural research can garner more evidence to clearly state how the three constructs differ.

In conclusion, the only similarities between Machiavellianism, narcissism and psychopathy, and possibly that which puts them all under the banner of the Dark Triad, is that they are all duplicitous, disagreeable, aggressive, and have mostly short-term mating strategies. On the other hand there are differences in the aggression, and in genetic and environmental factors, Big Five personality traits, strategies with regards to goals and motives, and self-view. Therefore it is most viable that Machiavellianism, narcissism and psychopathy are overlapping but distinct constructs, a conclusion agreed upon by most current research (Chabrol, Van Leeuwen, Rodgers & Séjourné, 2009; Lau, 2010; Paulhus & Williams 2002; Jones & Paulhus, 2011; Vernon et al., 2007).


Brumbach, B. H., Figueredo, A. J., Ellis, B.J. (2009). Effects of harsh and unpredictable environments in adolescence on development of life history strategies: A Longitudinal Test of an Evolutionary Model. Human Nature, 20(1), 25-51.

Bushman, B. J., & Baumeister, R. F. (1998). Threatened egotism, narcissism, self-esteem, and direct and displaced aggression: Does self-love or self-hate lead to violence? Journal of Personality and Social Psychology, 75(1), 219-229. doi: 10.1037/0022-3514.75.1.219

Cale, E. M., & Lilienfeld, S. O. (2002). Sex differences in psychopathy and antisocial personality disorder: An integrative review. Clinical Psychology Review, 22, 1179–1207. doi: 10.1016/S0272-7358(01)00125-8

Campbell, J., Shermer, J. A., Villani, V. C., Nguyen, B., Vickers, L., & Vernon, P. A. (2009). A behavioural genetic study of the Dark Triad of personality and moral development. Twin Research and Human Genetics, 12, 132-136. doi:10.1375/twin.12.2.132

Chabrol, H., Van Leeuwen, N., Rodgers, R., & Séjourné, N. (2009). Contributions of psychopathic, narcissistic, Machiavellian, and sadistic personality traits to juvenile delinquency. Personality and Individual Differences, 47(7), 734-739. doi: 10.1016/j.paid.2009.06.020

Gabriel, M. T., Critelli, J. W., & Ee, J. S. (1994). Narcissistic Illusions in Self-Evaluations of Intelligence and Attractiveness. Journal of Personality, 62(1), 143-155. doi: 10.1111/j.1467-6494.1994.tb00798.x

Gupta, M. D. (1991). Effects of impulsiveness and age on Machiavellianism. Indian Journal of Psychometry  and Education, 22,  19-25.

Gustafson, S. B., & Ritzer, D. R. (1995). The dark side of normal: A psychopathy-linked pattern called aberrant self-promotion. European Journal of Personality, 9, 147-183.

Holtzman, N. S., & Strube, M. J. (2010). Narcissism and attractiveness. Journal of Research in Personality, 44(1), 133-136. doi: 10.1016/j.jrp.2009.10.004

Jakobwitz, S., & Egan, V. (2006). The dark triad and normal personality traits. Personality and Individual Differences, 40(2), 331-339.

Jonason, P. K., Li, N. P., Webster, G. W., Schmitt, D. P. (2009). The Dark Triad: Facilitating short-term mating in men. European Journal of Personality, 23, 5-18. doi: 10.1002/per.698

Jonason, P. K., Li, N. P., & Buss, D. M. (2010). The costs and benefits of the Dark Triad: Implications for mate poaching and mate retention tactics. Personality and Individual Differences, 48(4), 373-378. doi:

Jonason, P. K., & Webster, G. D. (2010). The Dirty Dozen: A concise measure of the Dark Triad. Psychological Assessment, 22, 420–432. doi:10.1037/a0019265

Jonason, P. K., Luevano, V. X., & Adams, H. M. (2012). How the Dark Triad traits predict relationship choices. Personality and Individual Differences, 53(3), 180-184. doi: 10.1016/j.paid.2012.03.007

Jones, D.N., & Paulhus, D.L. (2010).  Different provocations trigger aggression in narcissists and psychopaths. Social and Personality Psychology Science, 1, 12-18.

Jones, D. N., & Paulhus, D. L. (2011). Differentiating the Dark Triad within the interpersonal circumplex. In L. M. Horowitz & S. Strack, Handbook of interpersonal psychology: Theory, research, assessment, and therapeutic interventions (249-269). New York: Wiley & Sons.

Larsson, H., Andershed, H., Lichtenstein, P. (2006). A genetic factor explains most of the variation in the psychopathic personality. Journal of Abnormal Psychology, 115(2), 221-230. doi: 10.1037/0021-843X.115.2.221

Lau, K. S. L. (2010). Exploring Narcissism, Psychopathy, and Machiavellianism in Youth: An Examination of Associations with Antisocial Behavior and Aggression (Master’s Thesis, University of New Orleans). Retrieved from

McHoskey, J. W., Worzel, W., & Szyarto, C. (1998). Machiavellianism and psychopathy. Journal of Personality and Social Psychology, 74(1), 192-210. doi: 10.1037/0022-3514.74.1.192

Miller, J. D., & Campbell, W. K. (2008). Comparing clinical and social-personality conceptualizations of narcissism. Journal of Personality, 76, 449–476.

Miller, J. D., Dir, A., Gentile, B., Wilson, L., Pryor, L. R., & Campbell, W. K. (2010). Searching for a Vulnerable Dark Triad: Comparing Factor 2 Psychopathy, Vulnerable Narcissism, and Borderline
Personality Disorder. Journal of Personality, 78(5), 1529-1564. doi: 10.1111/j.1467-6494.2010.00660.x

Paulhus, D. L., & Williams, K. M. (2002). The Dark Triad of personality: Narcissism, Machiavellianism, and psychopathy. Journal of Research in Personality, 36, 556–563. doi:10.1016/S0092-6566(02)00505-6

Raskin, R., & Hall, C. S. (1979). A Narcissistic Personality Inventory. Psychological Reports, 45, 590.

Rauthmann, J. F., & Kolar, G. P. (2012). How “dark” are the Dark Triad traits? Examining the perceived darkness of narcissism, Machiavellianism, and psychopathy. Personality and Individual Differences, 53(7), 884-889. doi: 10.1016/j.paid.2012.06.020

Reise, S. P. & Wright, T. M. (1996). Personality traits, Cluster B personality disorders, and sociosexuality. Journal of Research in Personality, 30(1), 128-136. doi: 10.1006/jrpe.1996.0009

Rhodewalt, F., & Morf, C. C. (1995). Self and Interpersonal Correlates of the Narcissistic Personality-Inventory – A Review and New Findings. [Article]. Journal of Research in Personality, 29(1), 1-23. doi: 10.1006/jrpe.1995.1001

Sedikides, C., Rudich, E. A., Gregg, A. P., Kumashiro, M., Rusbult, C. (2004). Are Normal Narcissists Psychologically Healthy?: Self-Esteem Matters. Journal of Personality and Social Psychology, 87(3), 400-416. doi: 10.1037/0022-3514.87.3.400

Seto, M. C., Khattar, N. A., Lalumière, M. L., & Quinsey, V. L. (1997). Deception and sexual strategy in psychopathy. Personality and Individual Differences, 22(3), 301-307. doi: 10.1016/s0191-8869(96)00212-7

Taylor, S. E., & Armor, D. A. (1996). Positive Illusions and Coping with Adversity. Journal of Personality, 64(4), 873-898. doi: 10.1111/j.1467-6494.1996.tb00947.x

Vernon, P. A., Villani, V. C., Vickers, L. C., & Harris, J. A. (2008). A behavioral genetic investigation of the Dark Triad and the Big 5. Personality and Individual Differences, 44(2), 445-452. doi: 10.1016/j.paid.2007.09.007

3 Benefits of Chocolate

Posted on Updated on

The most important thing I learnt from this human physiology course I’ve just completed is this: three reasons why you should eat chocolate!

1. Phenylethylamine – this is a chemical in chocolate that releases endorphins in the body. Endorphins are naturally occurring opioids, and opioids are things that reduce pain and make you happy

2. Tryptophan – this is a chemical that helps release serotonin in the body. It whizzes around the body releasing serotonin from places. Low serotonin levels have been directly correlated to depression, so having more serotonin in the body = less depressed! Huzzah! (Yes, an oversimplification, but I’m sure all can attest to the feelings of happiness induced by the consumption of pure, velvety, chocolate).

3. Theobromine – a chemical that is similar to caffeine in that it keeps you awake. It is a lot stronger than caffeine though, so it will keep you a whole lot more awake, but it does not last as long. Good for short bursts of energy during your exams!

During times of stress (ie exam period), everyone experiences a lack of sleep. Lack of sleep releases more cotisol, which mobilise amino acids to go through gluconeogenesis because the body really needs more glucose in the brain!

When you’re stressed or when your circadian rhythm is disrupted, your hypothalamus is stimulated and then the pituitary gland is stimulated to produce adrenocorticotropic hormone (ACTH), which swims through your blood stream til it gets to your adrenals. Your adrenal glands then release glucocorticoids to try and generate more sugar:

1. the amino acids in your muscles will break down (less muscle mass!)
2. fats from your adipose tissue will mobilise in to action
3. amino acids will break down and go through gluconeogenesis in the liver

The adrenals will also send signals to the brain to stop producing ACTH and other hormones so that this production of glucose will stop when you have enough.


The adrenal gland is also where androgens can be produced. Androgens are the hormones that cause male characteristics (remember though, everyone has androgens and estrogens, it’s just that males have more androgens and females have much less). So what happens is you have this over-stimulation of the bit where glucocorticoids are produced, and so you produce more androgens as well! Androgens make you more feisty (ex/ higher testosterone is correlated to higher aggression in animals, and higher ‘dominance’ in men, which could manifest as violence). So that’s where the weird restlessness and frustration is coming from during prolonged stress. Androgens also help in weakening the immune system, which is one way stress causes sickness.

Stress also suppresses the immune system because… oh wait I have gone on a rather long tangent haven’t I?

Back to the point of this post. Chocolate is good for you because it makes you happy and awake, and being happy is good for you because that means you are not frustrated or stressed, which is good for you because your immune system won’t be destroyed, so you won’t get sick so easily! Huzzah! CHOCOLATE!

PS. If you want to study for a long period of time, my lecturer recommends a mocha, because it has caffeine AND theobromine!

Chocolate and trp

Posted on Updated on



Today in biology we learnt about the mechanisms of positive and negative feedback loops in regulating transcription. In particular, we learnt about tryptophan (trp) operons. The trp operon uses negative feedback and basically encodes the enzyme for the biosynthesis of tryptophan. This doesn’t happen if you already have tryptophan, which can happen two ways: either your body makes them or you eat something that has it. One source of trp is… chocolate! Apparently trp helps in releasing serotonin which is (very) basically the happy chemical. So high trp means more serotonin which means awesome happy fun times.

However, trp is a co-repressor. It helps to repress the enzyme that’s actually making trp in your body. So, there’s an enzyme or gene or something that makes trp, but when the trp is made, it goes back to this enzyme, which has a repressor on it and the trp binds to the repressor, therefore deactivating it! And so your body stops making trp.

Basically, you get happy because of seratonin because of trp, but then your body’s like “woop! too much happy! better stop making happy!” and then shuts down the trp factory which shuts down the serotonin factory. (There is probably another gene or protein that aids in the release of serotonin from elsewhere, but we haven’t learnt about it so it doesn’t exist yet). So if your body’s stopped making trp then I guess the only way to be more happy is to eat more chocolate!