Rats and mice normally flee if they smell cat urine, but not if they're infected by the protozoan parasite Toxoplasma gondii. The parasite can only complete its life cycle if its rodent host is eaten by a cat, so it "brainwashes" the creature into apparently liking the scent.

Now Ajai Vyas and his colleagues at Stanford University in California, US, have revealed that the brainwashing is surgically precise. The parasites seem to reverse the rodent's innate fear by interfering with the amygdala, the seat of conditioned responses in the brain. Vyas's team looked at the distribution of the parasite in the brain of infected rats, and found it was almost twice as dense in the amygdala.

The exquisite precision leaves intact all other neurological mechanisms for learning to avoid danger, so the rodents learn to survive all hazards except being eaten by cats \ufffd the only form of death beneficial to the parasite.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0608310104)