Clues about how the parasites affect the animal come from several observations. First, the density of cysts in the amygdala is almost double that in other brain structures involved in odor perception. Parts of the amygdala have been linked to anxiety and the sensation of fear. Second, the genome of T. gondii contains two genes related to mammalian genes involved in the regulation of dopamine, the molecule associated with reward and pleasure signals in the brain, including in ours. So perhaps the creepy protozoa makes suicidal activities, such as hanging around places frequented by cats, feel more pleasurable for the infected rodent?
What elevates this vignette about evolution and life in the wild to epic proportions for humanity is that about a tenth of the U.S. population is infected by T. gondii (in some countries, such as France, the infection rate is seven to eight times higher, possibly because of the widespread consumption of uncooked and undercooked meat). Human toxoplasmosis is usually considered to be symptom-free (what doctors refer to as asymptomatic). Exceptions are patients with a weakened immune system and the unborn (hence the need for pregnant women to avoid cleaning cat-litter boxes).
Science has known for a long time that schizophrenic patients are two to three times more likely to carry antibodies to T. gondii than are controls who are not schizophrenic. Furthermore, antipsychotic drugs that block the action of dopamine, such as haloperidol, commonly used in the treatment of schizophrenia, are also effective in combating toxoplasmosis in both rats and people. And some infected adults go on to develop psychotic symptoms similar to schizophrenia. Little is known about the mode or site of action of this pathogen in the human brain. The exact link between T. gondii and psychiatric diseases is tantalizing but remains murky.
Recent claims go so far as to argue for a role of T. gondii in shaping distinct cultural habits, depending on the rate of infection in the population. A prospective study tracking the road safety in Czech recruits during their 18 months of compulsory military draft found a rate of accidents six times higher in affected drivers. Are the young men with toxoplasmosis infection simply slowed down? Or do they drive more aggressively?
In my November 2009 column, I described the discovery by cognitive neuroscientists that the feeling of freely willing an action (called authorship or agency) is a subjective, conscious sensation no different, in principle, from the conscious awareness of seeing the azure blue sky or feeling the sharp pain of a toothache. When I engage in a dangerous pursuit, such as taking the end of the rope on a steep section of a granite wall in Yosemite Valley while climbing, I feel as if “I freely decided” to do so, whatever this might mean in a metaphysical sense. Yet my action is most likely caused by an inexhaustible multiplicity of factors not accessible to my conscious introspection, including, yes, possibly some tiny single-celled parasites lodging in my brain and making me act out their silent commands. The wonder of it all.
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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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