I keep up with research on schizophrenia because my brother Steve has it. (Hence, reading Deleuze and Guattari is always a little strange for me, shall we say.) One hypothesis is that a neurotoxin released by toxoplasmosis gives rise to symptoms of schizophrenia and possibly Alzheimer's. Toxoplasmosis is caused by Toxoplasma gondii, a protozoan symbiont that lives in most people's brains harmlessly. Cats are common hosts, and cat poop contains a lot of the protozoans. One theory is that cat poop near to pregnant humans is a way for the symbiont to jump. One in five of us humans carry the symbiont.