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Psyche Parasites

[ 11 ] February 2, 2010

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Psyche Parasites

Parasites, hosts, and behavioral manipulation

Imagine –

A cunning little larva has finally reached adolescence and at last emerges from her watery home.  She slithers along until she comes upon a big green monster that leaps and bounds over vast stretches of earth, boisterously singing as he gambols about.  The bouncing behemoth swallows her and she soon takes residence in a large dark void inside his stomach.

There she harbors a grave malice matched in wickedness by few other creatures.

Her sinister moment comes only when she has grown old enough and large enough — she hastily releases her noxious poison into the beast, corrupting its mind and sending it into a suicidal frenzy. The creature’s once graceful leaping – now reduced to clumsy hurdling – sends it to its doom in a nearby watering hole, where it drowns in seconds.  Our slithering protagonist exits from the rear of the spongy corpse, and lays its eggs in water that will soon bear a future generation of these dogged, brain-washing larvae.


The above may sound like a bad sci-fi movie or a Disney cartoon gone wrong; however, the phenomenon depicted (albeit somewhat melodramatically) is a real, natural occurrence.  The parasitic worms Spinochordodes tellinii use crickets and grasshoppers as their hosts, and after developing in the host’s gut, the parasite manages to manipulate the insect’s behavior, against all natural instinct, causing a suicidal leap into a body of water, where the parasite ultimately reproduces.  How does a tiny parasitic worm like S. tellinii manage to hijack the nervous system of a cricket and send it on a suicidal death leap?

It turns out that parasites often have a lot more to do with their host’s nervous system than we think. Though the exact mechanisms behind parasite-induced behavioral manipulations remain undiscovered, examples of this phenomenon abound.

One of the hottest new behavior manipulators is the infamous protozoan parasite Toxoplasma gondiiT. gondii is best known for its toxic effects on developing fetuses, hence the fear most pregnant women rightfully have of anything having to do with cat excrement (where the parasite lives after reproducing in the cat’s gut).  Besides causing nasty birth defects, T. gondii has been shown to cause some very peculiar behavioral effects in some of its “secondary” hosts (felines are the “primary” hosts).

Ground breaking research in England and at Stanford has shown that when a rodent – a lab rat in these studies – is infected with the parasite, it not only shows reduced fear of cat urine (a powerful innate fear that most rodent species have), but a slight attraction to it!

Somehow, the parasite manages to float around in the rodent’s blood stream, get off at the right stop in the fear center of the rodent’s brain (the amygdala in this case), deactivate the “fear-of-cat-urine” module, and in a bizarre encore, pop over to the dopaminergic pathway and turn on the attraction switch when the rat smells cat urine, ultimately turning a deep, innate fear into a slight attraction.  Of particular interest is the fact that diminished aversion to cat odor was found to be the only behavioral pattern affected by T. gondii infection (Vyas et al, 2007).

In other words, when the parasite infects an animal preyed on by felines it is able to alter a specific behavior in the animal in order to increase its chance of getting to the fertile reproducing ground that is the feline gut.

This would be akin to you finally shaking a life-long, debilitating fear of heights because of a microscopic one-celled organism you accidentally ingested in your morning cereal.

Interestingly, some recent stirrings do point to effects of T. gondii on human behavior. Most of this work concerns T. gondii’s “subtle effects on personality and psychomotor performance.”  Differences between infected and uninfected individuals have been found relating to one’s ability to concentrate, superego strength, and even the likelihood of getting into automobile accidents.  Furthermore, a statistical correlation between T. gondii infection and schizophrenia has been found in recent research.  This correlation has been supported by research revealing that Toxoplasma gondii can increase dopamine levels in its host’s brain; dopamine is thought to be a central player in schizophrenia.

Though these data are still young, a possible underlying mechanism of behavioral manipulation by Toxoplasma gondii in both rats and humans may soon be found, and further research would need to explain how Toxoplasma gondii cysts “know” how to migrate to their host’s amygdala and “know” how to turn off some behaviors without affecting many other ones.

Ultimately, parasites may play a larger role in our psyche then we want to believe.  A humbling thought, though not a very new one – massive steps in animal evolution have been attributed to a constant struggle against parasites (including the creation of the sexes), and the sheer magnitude of the immune system is a good indicator of this 3-billion-year-old reality.

“Neuro-Parasitologist” may very well be a new title in the ’10s.  They certainly have their work cut out for them.



[ 67 ] January 14, 2010

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The cognitive psychology of categorizing the animate and inanimate

When I think of my interests as a preschooler and kindergartner certain images form in my head, most of them recalling my avant-garde portraiture, a somewhat violent obsession with dinosaurs, and frequent daydreaming about bringing my pet lizards (carefully named “lizard” and “lizzy”) into class and unleashing them into a frenzied, screaming room.  Like most children, I was keenly interested in living things.

There is no doubt that early in their lives, children show a certain distinct concern for animate objects.  That’s not to say they don’t show an eager interest in inanimate objects as well.  At any rate, research has shown that children as young as 4 years old have a rather sophisticated understanding of the difference between what is alive and what is not (though they surely make mistakes…see Piaget’s 1929 work on “animism”).  Young children usually understand that plastic shovels do not feel sad or run away from home, that’s the business of cats and dogs; and pigeons are not meant to be picked up and used to displace sand, that‘s the business of plastic shovels.

There is a good deal of debate about the structure, evolution, and development of the inanimate-animate distinction.  It is generally thought to be an evolved cognitive mechanism, though there is some strong backlash to that idea (Farah et al resolutely referred to the idea of an evolved ability to distinguish animate and inanimate objects  as, “an a priori implausible hypothesis.”  backlash, indeed).  Either way, many cognitive scientists aspire to achieve a more thorough understanding of this ability, and some compelling new research out of Harvard has produced some strange, though telling, results.

It is known that separate regions of the ventral visual pathway categorize objects as nonliving and living.  Different groups of cells in different regions of the ventral visual pathway respond to either inanimate (medial ventral stream) or animate (occipital-temporal cortex) objects.  Furthermore, while other sensory modes play a role (like hearing and touch), visual cues, especially about the movement of objects, are thought to be central to the animate/inanimate categorization ability.  Whether this “neural specialization” is formed by sensory experience or is built into the architecture of the brain is not known, though new work by Mahon et al (2009) implies the latter.

By comparing groups of blind and seeing adults, Mahon et al came to the startling conclusion that living vs. non-living categorization in the ventral visual pathway does not require visual experience.  When prompted to think about living and non-living objects, subjects who were blind since birth showed overlapping fMRI BOLD (blood oxygen-level dependent) responses with the sighted subjects; that is, the areas of the visual cortex that categorize differences between inanimate and animate objects in seeing adults appears to function identically in congenitally blind adults. How is this possible?  How can an individual that has never seen a dog, a person, or a chair (or anything at all) show object categorization in the visual areas of their brain?

Mahon et al believe they’re close to an answer.  They write:

“One framework that can accommodate our findings views category-specific regions of the ventral stream as parts of broader neural circuits within the brain that are innately disposed to handle information about different domains of objects (Mahon et al, 2009, emphasis added).”

In other words, the brain doesn’t need visual experiences to categorize living and non-living things because it is built to do so before birth.  Visual experience may act to increase the resolution of this categorization and provide the individual with real-world examples, but it is not required to initially shape the visual cortex.

This idea is inspired by the “domain-specific” approach to cognitive psychology, which maintains that evolution shapes specific cognitive programs that help elicit specific behaviors in the animal that are relevant to specific pressures from the environment.

According to this line of thought, the brain is much like a cluster of machines within a machine.  These machines communicate with and rely on each other, but also have their own distinct functions.   Each “machine” helps to enhance the evolutionary fitness of the animal:  One machine helps us recognize faces in order to facilitate complex social interactions, another machine helps us recognize depth so we avoid fatal falls (my “depth machine” is particularly sensitive), and perhaps another builds animate vs. inanimate categories into our visual system, thus making it easier for us to notice that important difference in the world, and tell, say, predator from landscape.

To end with a digression, I propose that the amusing nature of an erroneous or confused calculation by our “animacy machine” could be a product of the machine’s innateness.  Moments when we swear our clocks are looking at us, sigh at wilting flowers, or believe our computers are malicious villains meant to tirelessly test our patience, are exceptionally resonant, and that may be because they go against the grain of a normal pattern of thought.   Perhaps it is due to our instinctual and skillful classification of the living and non-living that we find wit in animating the inanimate.

VG sunflowers

The Face Function

[ 10 ] January 7, 2010


The Face Function

The form and function of our facial expressions

Norman Bates is coming for Lila Crane.

Gripped with fear, Lila dashes to the cellar to escape the approaching madman, her eyes wide with panic, senses heightened.  You, the observer, similarly emote, as if there was a dark deadly figure lurking around your living room, waiting for the right moment before he (or she…or in this case, he-she) strikes.  But your expression soon transforms – when Lila discovers the mummified old lady in the cellar you gasp, or perhaps shriek in some kind of dissonant harmony with her, and then squint and wrinkle your nose.  After all, that mummy is just plain disgusting.

If you haven’t seen Hitchcock’s horror masterpiece the above may sound like nonsense, though you can certainly empathize with the primary emotions expressed:  fear, here initiated by impending violence; and disgust, elicited by the sight (and, perhaps, smell) of a mummified old woman.  I can’t imagine responding to either of these situations with, say, a smile or a laugh (unless you have seen Psycho enough times that Hitchcock’s sharp eye and Bernard Herrmann’s famed score gives you the movie-nerd-giggles, in spite of the terrifying action on-screen).

Human facial expressions are universal. There is no culture that expresses fear with a blissful smile, no country whose denizens frown with laughter.  The reason(s) why facial expressions are so culturally invariant are not fully understood.  The conventional knowledge is that facial expressions play an important social role in terms of deciphering your peers’ desires, motivations, and beliefs, and are thus unchanging.  It would be difficult for an individual to form normal social bonds if their expressions were unrecognizable.  The maladaptivity of some kind of novel facial expressions would likely result in a disabled social life and would be a particularly short-lived evolutionary trait.

But why do our expressions physically look the way they do?  Why is a smile upturned, a frown down?  Why do we open our eyes in fear and close them in pleasure?  One answer would be that facial expressions are social signals that have arbitrary physical properties and only mean what they do because we’ve given them their meaning – like articles of language or fashion trends.  Joshua Susskind of the University of Toronto believes otherwise – his research reveals that we cringe in disgust and widen our face in fear because there are physical properties of those expressions themselves that may help us respond to the kind of situations that cause disgust or fear.

Susskind looked at the physical properties of these two easily rendered facial expressions – fear and disgustFear is associated with enhanced sensory exposure: eye lids open up, the brow raises, and the nasal passage is widened. Disgust is associated with the rejection of sensory stimulation: the eye lids close, the brow lowers, and the nasal passage is constricted.  But these are just descriptive factors about the changes in facial “form” brought about by the two expressions – what about changes in function?

Respecting the evolutionary biology axiom “form fits function,” Susskind studied how actual sensory perception was altered by the onset of fear and disgust.  He had individuals accurately “pose” both expressions along with a ‘neutral’ expression, and complete certain sensory tasks.

His hypothesis was supported – fear led to a widened, more complete visual field as opposed to the neutral condition; disgust led to a reduction of the visual field.  Fear led to an increase in saccadic eye movements (which helps individuals “sample” their visual field more efficiently) while disgust showed a slight slowing of eye movements.  Lastly, fear allowed more air through the nasal passage, disgust did the opposite.  All of these results support the idea that fear may look the way it does because it is serving an important function for the individual – it “heightens” the senses and could facilitate the recognition of a potential threat (fear is, of course, a response to a “threat” of some kind, real or imagined).  Disgust may look the way it does because it constricts certain senses – bad smells are indicators of noxious substances, and your body rightfully rejects potentially dangerous, unsightly things (like, say, mummified bodies or bacteria-infested food).

Ultimately, facial expressions may have evolved for the direct benefits they provide to the organism on which they’re displayed.  Perhaps the physical properties of expressions were later co-opted for use in social interaction (evolution is remarkably klugey).  More evidence is needed to support this assertion, as is usually the case for similar “adaptive” explanations, but it is a compelling one nonetheless.  It also helps explain the universality of facial expressions – as ten toes help all humans balance and ten fingers help us grasp, fearful, alerted eyes help us spot looming dangers and a crumpled nose helps us avoid pestilence.

I look forward to a forthcoming explanation of the smile or the glare, and it would not surprise me if at least some facial expressions are purely social in function.  That is certainly the case when it comes to facially-driven behaviors such as deceit.  In being deceitful, we use the usually “honest” signal that is our face to be dishonest and manipulate others.  Here, the function of the expression is not what it does for us directly, as when fear enhances our vision, but what its interpretation by others does for us in the future – it is a purely social tool.

And with that, Mr. Norman Bates will have the last word:

“I think I must have one of those faces you can’t help believing.”


Locomotion and Our Moral Notion

[ 11 ] December 25, 2009


Locomotion and Our Moral Notion

Is there a universal moral grammar?

Debates about a human “moral sense” often spotlight the innumerable set of “taboos” that exist along cultural lines. These debates tend to confirm the common belief that culture cultivates a kind of context-dependent, moral-sentiment mélange in the psychology of its citizens which holds the group together and allows for both praise and punishment of, respectively, conformers and villains.  However, many of these rules (though there are obvious exceptions) are downright, and sometimes comically, arbitrary.

A taste:

“Do not use elevators from Friday night to Saturday night”

“Don’t wear blue in my neighborhood”

“Utter the phrase ‘excuse me’ when gas from your digestive tract is released through your mouth”

While these group-specific rules may elicit strong moral feelings in those who abide by them, it is not the rule itself that holds any moral weight (i.e. “please” is just a six-letter word); it is the fact that it is agreed upon among those who follow it that really matters, and ultimately leads to a judgment of an individual’s moral character (“that man is awfully rude…he has no manners at all!”).

This piece of the morality puzzle is most convincingly explained by the importance of upholding a tight alliance structure with your peers (see the exceptional research of Rob Kurzban at the University of Pennsylvania for details on this and many other bright ideas), though there is a multitude of other explanations for the existence of “arbitrary” or “taboo” morality, and there are surely more to come.

Yet I am more intrigued by those moral sentiments that exist cross-culturally – morals that don’t separate one group from another but bind them all together and constitute a “human moral sense.” New research in this realm by cognitive neuroscientists, psychologists, evolutionary biologists, and lawyers, has begun to unearth a “universal moral grammar” that has specific neural substrates, coherent adaptive design features, and interesting correlates in centuries and centuries of human law and philosophy.

Hold on – let me rewind one sentence. In the above list of occupational investigators, the answer to the question “which of these does not belong?” seems laughably obvious.

Trust a lawyer on the structure of morality?  Ha!

A man who never graduated from school might steal from a freight car. But a man who attends college and graduates as a lawyer might steal the whole railroad.”  – Teddy Roosevelt

Wisecracks aside, John Mikhail, a lawyer from Georgetown University Law Center, has one of the stronger theories of a universal human moral sense around, and also managed to get it published in a prominent cognitive science journal (Mikhail, 2007, see link for citation).  “Whole railroad” indeed.

Mikhail cites Noam Chomsky as a theoretical inspiration. Noam Chomsky’s “universal grammar” theory of linguistics has proven to be one of the most influential cognitive theories of the past century.  In brief, his theory pushed the view that a universal set of grammatical principles exists across languages, and implies an innate, evolved sense of what constitutes a “correct sentence,” independent of the language within which it is uttered.  Mikhail, inspired by Chomsky’s program, argues for a similar set of innate rules, though these are rules that apply to moral judgments rather than linguistic judgments; a “universal moral grammar.”  Perhaps loosely inspired by Teddy’s quip, Mikhail uses as his prime experimental example one of the more famous (and often loathed) moral dilemmas of the modern era:  “the trolley problem.”

For those not familiar with the dreaded locomotive, let me offer a brief description of a common iteration of the trolley problem, lifted straight from Mikhail:

A runaway trolley is about to run over and kill five people, but a bystander who is standing on a footbridge can shove a man in front of the train, saving the five people but killing the man. Is it permissible to shove the man?

Across cultures, genders, ages, and races, the result is essentially the same and has been replicated countless times: over 90% of respondents consider this act impermissible.

Theorists who believe humans naturally act in the interest of the many rather than the few surely can’t explain this result – we are not imbued with a natural Utilitarian sense of “the greatest good for the greatest number,” though we can be taught this idea.  Incidentally, in many of these experiments the subjects are asked to explain their responses and find themselves lost for words, referring to their decision as illogical, irrational, and simply intuitive rather than rationally justified (Mikhail, 2007).

While there are obvious issues with trolley problem experiments – the question is too sensational, it’s an unlikely if impossible situation, there is no choice to opt out and attempt to save everyone – the ubiquity of the results and the subjects’ subsequent bewilderment and incapacity to explain their choices make it a very compelling conundrum.  Furthermore, an equally persuasive result is found with what I’ll call the “switch” trolley problem:

A runaway trolley is about to run over and kill five people, but a bystander can pull a switch that will turn the trolley onto a side track, where it will kill only one person.  Is it permissible to pull the switch?

The cross-cultural, cross-gender, cross-racial result?  Around 95% consider this act permissible.

Clearly there must be a considerable difference between these two acts if one is so acceptable, the other, forbidden.  Additionally, people can’t explain why one is “better” than the other besides the basic perception that the act of pushing the man just seems worse than the act of pulling the switch.  Mikhail digs deeper.

He argues that when we analyze these problems we are actually parsing through a handful of structural properties of the stimulus (the stimulus being the trolley problem itself) that aren’t there on the surface and may not even enter into our consciousness at all.

He defines these substructures as means, ends, side effects, and prima facie wrongs (like battery).  Here’s how it breaks down for the “push the man” problem:

Means (arranged temporally)

-touching the man [committing battery]

-throwing the man [again committing battery]

-causing train to hit man [that’s battery #3]


-preventing train from hitting men

Side Effects

-committing homicide

Here, three “wrongs” (batteries) lead to one “right” (safety of five men) and another wrong (death of one man).  The psychological math is not based on a “save-as-many-people-as-possible” principle, but an “avoid-committing-battery” principle. Thus, the act feels impermissible.  The subject answers accordingly (I use the word “feels” because the subject cannot rationally explain their decision; it is seemingly driven by sub-conscious mechanisms, though these need not be limited to emotions).

Here’s how it breaks down for the “switch” problem:

Means (arranged temporally)

-throwing the switch

-turning the train


-preventing train from hitting men

Side Effects

-causing train to hit man [committing battery]

-committing homicide

Here, the “wrongs” occur as side effects, the means appear innocuous, and the same “rightful” end is achieved.   The act feels permissible.

Mikhail buffers these examples with more textured ones that involve detailed scenarios (i.e. throwing a switch that collapses a bridge above the tracks where one man is standing, thus saving the five – only one battery as a means this time) and finds that the impermissible/permissible responses end up somewhere in the middle.  Actually, the math works beautifully – the more acts of battery as a means, the higher percentage of “impermissible” responses.

The next step is to figure out the neurophysiological mechanisms that underlie this complex, systematic behavior.  There’s no doubt it involves both emotional and analytical brain regions.  Current research supports this idea, and points to a consistent network of activation in the anterior prefrontal cortex, medial and lateral orbitofrontal cortex, dorsolateral and ventromedial prefrontal cortex, anterior temporal lobes, and the posterior cingulate region.  This research is in its early stages, and it will be fun to watch more information emerge about the neural correlates of moral cognition.

In the end, it is the combination of three facts that make Mikhail’s universal moral grammar theory – the idea that there is an innate set of mechanisms that parse through relevant aspects of moral dilemmas – so compelling:

1)  The moral judgments that trolley problems educe are rapid, confident, and described as “gut feelings” and “intuitions.”

2)  The judgments are notably cross-demographical.

3)  The judgments are difficult to describe and thus seem to occur beneath rational consciousness and logical reasoning.

The next big question: Mikhail refers to “prima facie wrongs” (i.e. battery) that have weight in our moral decisions. What are these wrongs and how did they wedge themselves into the natural order of the human mind? Perhaps the answer will turn out to be an aesthetic one…maybe more visceral acts (such as battery) carry extra moral weight, regardless of their outcomes and side effects?  This is a mere musing, but an interesting one nonetheless.

But those are questions for another day.  Now, in all seriousness, I have to go catch a trolley.

(Hopefully the city of Philadelphia has cleared the tracks of snow…and human beings).

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