In most cases, he said, "they do something terribly unsubtle, like destroying the vision, so [infected animals] are much less capable of avoiding predators."
T. gondii, by contrast, "is not just sledge-hammering a behavior out of existence," Sapolsky said.
"It's extinguishing a normal behavior"—avoidance of cats—"and replacing it with this incredibly maladaptive opposite."
(Read related story: "Suicide Grasshoppers Brainwashed by Parasite Worms" [September 1, 2005].)
Vyas's team found that Toxoplasma, which forms cysts in the brain, tends to concentrate in an area of the brain called the amygdala.
Because that region is linked to fear and anxiety, the finding provides a new clue to how the parasite manipulates behavior.
Sapolsky, Vyas, and their colleagues reported their findings Monday in the Proceedings of the National Academy of Sciences.
Manuel Berdoy, a zoologist at Oxford University in England, called the new finding "a delight."
He and Joanne Webster, a researcher at Imperial College London, had previously found that Toxoplasma-infected rodents gravitated toward cat odors.
The new study advances scientists' understanding of how the parasite pulls off the trick, Berdoy said.
He called it "astonishing that [T. gondii] may be able to target specifically the neural pathways responsible for processing cat odors.
"It's incredible that the parasite would be able to alter a response—cat aversion—that is so ingrained in the rats' psyche," Berdoy said.
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