Stanford University scientists have discovered that the complex and intriguing reproductive strategy exhibited by the single-celled parasite Toxoplasma gondii relies on altering the rodent brain to interpret cat odors as sexually attractive. The new findings fill a gap in existing knowledge about a most peculiar parasite that one scientist believes could also be subtly rewiring human behavior.
It has long been known that Toxoplasma requires the cat digestive system to reproduce. Infected rodents, with a reduced fear response to cat odors, are more susceptible to predation by cats, thereby enabling completion of the parasite lifecycle.
The new study, authored by Patrick House and Dr. Robert Sapolsky, investigated how the parasite makes infected rodents more likely to spend time near cat odors. The study found that infected male rats have altered activation in brain regions involved in fear and increased activation of brain regions involved in sexual attraction after exposure to cat odors.
“These findings support the idea that in the rat, Toxoplasma is shifting the emotional salience of the detection of the cat. They also suggest that fear and attraction might lie on the same spectrum, or at least that the emotional processing of fear and attraction are not entirely unrelated,” House explained.
Around one-third of humans test positive for Toxoplasma, due largely to the consumption of undercooked meat or contact with cat litter. In humans, Toxoplasma exposure is most dangerous to developing fetuses and pregnant women. Recent studies have linked Toxoplasma exposure to schizophrenia, a disease noted for amygdala dysfunction and improper emotional response. Additionally, there is evidence from Europe that the parasite may be skewing gender balance.