Toxoplasma gondii is a tiny parasite that can infect humans. Adults often seem to show no symptoms from it.

While toxo can be acquired by ingesting contaminated food or water, it is basically a zoonotic disease; that is, it lives and reproduces in a reservoir of cats, but occasionally "jumps" to humans. It's shed in cat feces, so outdoor cats can contaminate soil and water, while indoor cats do the same for their litter boxes, making them hazardous especially for pregnant women to handle.

Toxo isn't spread directly, human-to-human or cat-to-cat. To infect cats, toxo first infects mice and rats, and hijacks their brains.

In a display of bizarre biology, a seemingly normal but toxo-infected mouse loses its fear of cats, becomes less risk-averse and more active, and finds cat urine sexually attractive. These Mighty Mouse wannabe's act fearless and aggressive, right up until they're devoured.

The toxo bug treats humans like it treats mice. That is, it hijacks human brains too. An "asymptomatic" infected human becomes less risk-averse and more active, but with a slower reaction time. To infected men, cat pee smells like perfume. Infected people are more likely to walk into traffic, and don't dodge when drivers honk. They're 2.6 times more likely than uninfected people to be involved in traffic accidents.

This is just a byproduct of toxo's evolution; humans don't generally satisfy the ultimate purpose of toxo's mouse-oriented machinery -- to infect cats, which can serve as a toxo condo.

This is just one example among countless others: a dysfunctional brain can produce behaviors and thoughts that seem autonomous and independent, but are in reality determined by electrochemical events within our brain tissues.

It's plenty common. Physical processes and events control our thoughts and behaviors in ways of which we're totally unaware. You might believe you can do what you want, but you certainly can't want what you want. You can decide whether to take a drink, but you can't decide whether to be thirsty. If you're thirsty enough, you will drink if you can, regardless of consequences up to and including death, like drinking seawater after many thirsty days in a lifeboat.

The brain generates thoughts, perceptions, interpretations, attitudes, judgments, behaviors. When the function of the brain is altered -- by purely physical phenomena such as a blow to the head, a drug, a tumor, a stroke -- the ability to assess, decide and act is correspondingly altered, depending on which component of the brain is affected. When the compromise is subtle, we might not even realize anything's amiss.

A prim and proper Sunday school teacher with high blood pressure leaks a little blood into a small part of her brain. She appears completely normal -- except now she cusses like a sailor.

During a briefly irregular heartbeat, a respected community leader "throws a clot," which blocks a small blood vessel in his brain. Afterward, he too seems quite normal, and functions well in almost every respect -- except now he tells dirty jokes at church socials and gleefully fondles any unwary young woman who strays within his reach.

Those who knew these people "before" are at first aghast, then saddened, at the changed behavior. Those who didn't know them might think it's all kind of funny.

Recent advances in neuroscience -- essentially, brain science -- have uncovered complex physical processes which generate our thoughts and behaviors. These findings should be profoundly disturbing to those who have taken for granted that our behavior is freely selected by an autonomous spirit, soul or ghost that inhabits this meat machine we call the human body.

Apart from its implications for free will, crime and punishment, sin and damnation, the fact that our brains are ourselves creates another problem -- for those inclined to believe in invisible spirits. Both medicine and the law recognize "brain death" Transplanted livers and kidneys live on, but when the brain is dead, the person is dead. If we absolutely require an intact brain to perceive, evaluate, experience and remember, those who maintain that the "real" self is an immaterial spirit which somehow survives physical death intact, self-aware and still functioning -- they got some serious splainin' to do.

In the absence of the organic computer we know as "brain," where would a disembodied soul's memories reside, how would they be stored, how could they be retrieved? With no memory, sensory, or emotional apparatus, how could one experience postmortem joy or pain, recognize deceased relatives, or "watch over" the living? Spooky magic?

For that matter, if this inner spook is non-material, not subject to physical influences, why is it so tightly imbedded in the physical body, and why does it only depart that entanglement when the brain's cells cease to function?

Those who recover from prolonged coma report no self-awareness while their higher brain centers weren't functioning. Likewise during general anesthesia. Yet when those same brain cells irreversibly die, we're told full conscious awareness suddenly pops back into reality as a sentient "soul."

Where has it been?

If soul-consciousness temporarily turns off when the brain temporarily turns off, why wouldn't it turn off permanently when the brain turns off permanently?

Fixation on this ancient soul-scam is only distracting and destructive in the here-and-now. When their brains finally do fade out, those who count on an afterlife to compensate for the travails of this one will simply be unable to realize what they're missing.

Jon Hauxwell, MD, is a retired family physician who grew up in Stockton and now lives outside Hays.

hauxwell@ruraltel.net