[jinx]

Originally Posted by Clodfobble

Fear is all in your head! Or at least it is for mice. That's what the Japanese researchers at Tokyo University set out to prove when they created a new breed of genetically modified mice that are not afraid of cats. By turning off certain smell receptors in the brains of their mice, the scientists were able to show that their newly-ballsy mice are only instinctively afraid of the predators' smell, rather than learning from experience that cats will gobble them up.

Mice and rats who are infected with toxoplasmosis (The "pregnant women shouldn't change the litter box" disease.) also have no fear of cats.

Behavioral changes

It has been found that the parasite has the ability to change the behavior of its host: infected rats and mice are less fearful of cats - in fact, some of the infected rats seek out cat-urine-marked areas. This effect is advantageous to the parasite, which will be able to sexually reproduce if its host is eaten by a cat.[12] The mechanism for this change is not completely understood, but there is evidence that toxoplasmosis infection raises dopamine levels in infected mice.


The findings of behavioral alteration in rats and mice have led some scientists to speculate that toxoplasma may have similar effects in humans, even in the latent phase that had previously been considered asymptomatic. Toxoplasma is one of a number of parasites that may alter their host's behaviour as a part of their life cycle. [13] The behaviors observed, if caused by the parasite, are likely due to infection and low-grade encephalitis, which is marked by the presence of cysts in the brain, which may produce or induce production of a neurotransmitter, possibly dopamine, [14] therefore acting similarly to dopamine reuptake inhibitor type antidepressants and stimulants.

"In populations where this parasite is very common, mass personality modification could result in cultural change. [Variations in the prevalence of Toxoplasma gondii] may explain a substantial proportion of human population differences we see in cultural aspects that relate to ego, money, material possessions, work and rules." — Kevin Lafferty [15]

Correlations have been found between latent Toxoplasma infections and various characteristics: [16]

• Decreased novelty-seeking behaviour [17]
• Slower reactions
• Lower rule-consciousness and jealousy (in men) [17]
• More warmth and conscientiousness (in women) [17]

The evidence for behavioral effects on humans, although intriguing, is relatively weak