Of cats, climbing and schizophrenia

Certainly Flegr’s thinking is jarringly unconventional. Starting in the early 1990s, he began to suspect that a single-celled parasite in the protozoan family was subtly manipulating his personality, causing him to behave in strange, often self-destructive ways. And if it was messing with his mind, he reasoned, it was probably doing the same to others.

The parasite, which is excreted by cats in their feces, is called Toxoplasma gondii (T. gondii or Toxo for short) and is the microbe that causes toxoplasmosis—the reason pregnant women are told to avoid cats’ litter boxes. Since the 1920s, doctors have recognized that a woman who becomes infected during pregnancy can transmit the disease to the fetus, in some cases resulting in severe brain damage or death. T. gondii is also a major threat to people with weakened immunity: in the early days of the AIDS epidemic, before good antiretroviral drugs were developed, it was to blame for the dementia that afflicted many patients at the disease’s end stage. Healthy children and adults, however, usually experience nothing worse than brief flu-like symptoms before quickly fighting off the protozoan, which thereafter lies dormant inside brain cells—or at least that’s the standard medical wisdom.

But if Flegr is right, the “latent” parasite may be quietly tweaking the connections between our neurons, changing our response to frightening situations, our trust in others, how outgoing we are, and even our preference for certain scents.
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Psychedelic as his claims may sound, many researchers, including such big names in neuroscience as Stanford’s Robert Sapolsky, think he could well be onto something. Flegr’s “studies are well conducted, and I can see no reason to doubt them,” Sapolsky tells me. Indeed, recent findings from Sapolsky’s lab and British groups suggest that the parasite is capable of extraordinary shenanigans. T. gondii, reports Sapolsky, can turn a rat’s strong innate aversion to cats into an attraction, luring it into the jaws of its No. 1 predator. Even more amazing is how it does this: the organism rewires circuits in parts of the brain that deal with such primal emotions as fear, anxiety, and sexual arousal. “Overall,” says Sapolsky, “this is wild, bizarre neurobiology.”