Do not adjust your set. We are in control.

Some students have gotten back to me after the lecture on predation and parasitism and were asking how parasites can control host behavior, and apparently so precisely. The short answer is that we have no clue. We know that parasites can make neuropeptides that have stronger effects on their target receptors than the host's own neuropeptides, but it is a long way from dosing the brain with neuropeptides or neurotransmitter mimics to getting a response that at least appears to be ordered. Simple brain damage seems wanting as an explanation as well, unless the parasites have chosen precisely the correct areas of the brain to damage.

In the rat-cat example, Toxoplasma gondii takes over the rat's interface with the world--the way sensory input is processed in the brain--and co-opts it for its own use in a way that decreases the rat's fitness. In the language of evolutionary biologists, that is a big bummer. Carl Zimmer is a writer for Science and has a great overview of the original rat experiment, and the general theme of parasites modifying your behavior.