The ancient debate surrounding the existence of free will appears unresolvable, a metaphysical question that generates much heat yet little light. Common sense and volumes of psychological and neuroscientific research reveal, however, that we are less free than we think we are. Our genes, our upbringing and our environment influence our behaviors in ways that often escape conscious control. Understanding this influence, the advertisement industry spent approximately half a trillion dollars worldwide in 2010 to shape the buying decisions of consumers. And extreme dictatorships, such as that in North Korea, remain in power through the effective use of insidious and all-pervasive forms of propaganda. Yet nothing approaches the perfidy of the one-celled organism Toxoplasma gondii, one of the most widespread of all parasitic protozoa. It takes over the brain of its host and makes it do things, even actions that will cause it to die, in the service of this nasty hitchhiker. It sounds like a cheesy Hollywood horror flick, except that it is for real.
We know that illness in general can slow us down, incapacitate us and, in the worst case, kill us. Yet this organism is much more specific. Natural selection has given rise to pathogens that infiltrate the nervous system and change that system’s wiring to achieve its ultimate purpose, replication—like a computer virus that reprograms an infected machine.
Such is the case with T. gondii. It sexually reproduces only in the intestines of cats yet can maintain itself indefinitely in any warm-blooded animal. Infected cats shed millions of their oocysts in their feces. Taken up by all kinds of animals, including dogs, rodents and humans, they infect muscle and the brain to escape attacks by the host’s immune system. Hidden away, they remain dormant as cysts, surrounding themselves with a tough cell wall. Yet this quiet stage of infection, called toxoplasmosis, is deceptive. Violating all rules of good hospitality, these invaders make the host’s brain do things counterproductive to its own survival.
Toxoplasmosis has been most thoroughly studied in rats and mice. Both species have a deep-seated, innate fear of cats for obvious reasons. Spray a bit of cat urine into a corner, and the rodent will avoid this location, well, like the plague. In contrast, an infected animal loses its innate fear of cats. By some measures, it even appears to be mildly attracted to the smell of felines. This is an unfortunate turn of events for the rodent, because it is now more likely to be successfully hunted by a cat. On the other hand, this is a great deal for T. gondii. When the cat devours the sick critter and its contaminated brain, T. gondii moves into its final host, where it reproduces, completing its life cycle. Not quite what the romantics have in mind when they write about “the circle of life”!
The behavioral manipulation induced by T. gondii is quite specific. The infected rodent doesn’t look sick; its weight is normal; it moves about normally, possibly a bit more frantically than other mice; it grooms itself; and it interacts routinely with its conspecifics. Think how different this case is from what happens in rabies, another nasty infection. The animal loses its instinctual shyness, aggressively attacking others (the proverbial mad dog), thereby spreading the rabies virus through its bite. But because T. gondii can reproduce only in felines, it wants its host to be eaten by cats, not by just any carnivore. And because cats hunt live prey and do not eat carrion, T. gondii must not immediately kill its temporary host.
Rodents Aren’t Superheroes
How does T. gondii effect its insidious changes in the host? Experiments by Joanne P. Webster of Imperial College London, Robert Sapolsky of Stanford University and others have shown that infected rats or mice do not turn into the murine equivalent of Siegfried, the hero of Wagner’s Ring who knew no fear. No, they still avoid open spaces, remain nocturnal creatures, retain their aversion to the urine of other predators and learn to fear a tone associated with a foot shock. Might the protozoa have stunted their smell? After all, if they cannot smell anything anymore, they would not know how to avoid places smelling of cat urine. But infected mice still avoid food if it smells different—an aversion that arose partly because for centuries humans have been trying to control rodents by poison. The infected mice also respond appropriately to the smell of their littermates.
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17 Comments
Add CommentA little silly to tie free will to a parasite, and not very successfully either... however, what a fantastic testament to nature's tenacity; to create such specificity in the tiniest of beings, and with such targeting intent. Thanks for calling attention to this protozoa.
Reply | Report Abuse | Link to thisI don't know about common sense, my suspicion is that it is as vaporous as free will. But I do know that doubts about free will are common in philosophy and religion, and this has been the case for thousands of years.
Reply | Report Abuse | Link to thisIt doesn't even have to be parasites like the one mentioned above. There are a myriad of bacterial organisms that call our bodies home.
Reply | Report Abuse | Link to thisTo think that none of them over the many millenia could have evolved to influence us to act toward the survival of their species would be naive.
We are not just human, we are an ecosystem and organisms in an ecosystem be they humans, beavers, or ants often alter their ecosystems to suit their needs.
"Im not going to work today, I have a BUG!!!!"
Reply | Report Abuse | Link to thisDr. Robert Sapolsky has a wonderful video where he explains the parasite infestation and its effects on the brain. You can find a link here: http://www.interfaces.com/blog/2010/05/neuro-parasites-problem-solving-errors/
Reply | Report Abuse | Link to thisI wonder if toxoplasmosis is a factor in the phenomenon of "cat ladies", eccentric women who live with many cats.
Reply | Report Abuse | Link to thisWe have no freewill that means anybody cheat us manipulate us it is possible without our consent?Real fact is that we by nature very credulous, not alter, some part play by our unconscious also but if we increase our thinking faculty before taking any decision think twice we can avoid the cheater.Thinking faculty can develop with practice. asking to every problem how and why,that way we get correct solution after all this practice also develop by error and correct the error
Reply | Report Abuse | Link to thisI recall when I first heard of this concept--namely, that bacterial or viral infections in the brain might alter cognition--I thought it was total bunk. Incidentally, there is no evidence that this is the case. Certainly, diseases of all sorts may alter brain function, but the effects of disease or infection on cognition are almost certainly indirect. Hence, it seems rather silly to speculate about whether infectious agents might specifically control mental function in any fashion. What's more likely: rats are "compelled" by toxoplasmosis to no longer fear cats, or infection impairs brain function non-specifically (or with an accidental specificity), which results in impaired fear responses to cat urine? What's more likely, that toxoplasmosis affects cell function, signaling or connectivity in the human brain which has a negative impact on outcome measures such as mental health, or that toxoplasmosis specifically "controls" brain function? There is a place for science and a place for fiction... and believe me, this appears to be more fiction than science.
Reply | Report Abuse | Link to thisBottom line, the idea that infectious agents have a direct impact on free will is highly dubious (not to mention that "free will" is an unscientific concept). Rather, it is much more likely that these agents negatively impact brain function in non-specific or random fashions--possibly affecting the "will", but not with any "intention" (even in the loosest sense of the word) guiding the process.
What a advancement in medicine this would be,if it be proven true!
Reply | Report Abuse | Link to thisI have IgG antibodies to Toxoplasma gondii, and sometimes I feel depressed, I even started believing that there is democracy in Spain. What can I do ?
Reply | Report Abuse | Link to thisGreat info, and comments (having been up all night working in survival mode etc., the thought of parasites influencing “free well” is somehow relaxing).
Reply | Report Abuse | Link to thisTo those harboring disbelief that this sort of thing can happen, blame it on the parasites? Think of two systems intertwined, each working for advantage, it is basic bio.
R. Carlson
Great info, and comments (having been up all night working in survival mode etc., the thought of parasites influencing “free well” is somehow relaxing).
Reply | Report Abuse | Link to thisTo those harboring disbelief that this sort of thing can happen, blame it on the parasites? Think of two systems intertwined, each working for advantage, it is basic bio.
R. Carlson
Stress and its effects on attention, and capacity for attention itself are possible areas of cognition that can be biologically open to influence.
Reply | Report Abuse | Link to thisThe incidence of cysting in the amygdala certainly points toward possible fear/anxiety correlation with infection, however it manifests.
Commentors in SA often wax a bit philosophical, rather than observational. Skepticism is part of scientific thought in that it promotes research to answer specific questions. Conjecture is best followed by gathering information and making falsifiable hypotheses to test. Casting vague opinion, often antiscientific in intent, is inappropriate comment.
What is the free will ?
Reply | Report Abuse | Link to thisWhy artificial intelligence doesn't work ?
Maybe the perceptron is a model of some bacterial network ? How does a neural network without parasites would compute ? Is our limited consciousness partly bacterial ?
(The replicators are free of bacteria, their AI works, lol)
I see that these scientists have very 'religious' views. They see genes, body, consciousness, etc. as separate matters. They are like religious people who separate 'body' and 'soul.' My whole body is 'me' and if my body wants something it's me want it, consciously or unconsciously. But I still can control my hunger or desire for sex. Even animals can control it. But Dominique Strauss-Kahn could not as many other hi-profile politicians. They are the subject of this 'discussion.'
Reply | Report Abuse | Link to thisNow I know why. I have never know anyone who owned a cat who wasn't a little on the strange side.
Reply | Report Abuse | Link to thisWe are free to make our own choices. But the options available to us are limited by circumstances, one of which could be a parasite which was able somehow to take away or limit one or more options, or to make some choice look more rewarding as an option than otherwise.
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