Bodily Defense

Abstract

Given the enormous importance of the human brain, one might think that our bodies would have evolved extensive safeguards to protect it from toxic compounds. Yet the brain is so easily intoxicated with some very common chemicals that we don’t even question it. Alcohol, nicotine, caffeine, heroin, methamphetamine, cocaine—they all travel in the blood, reach the cranium, and enter into the cerebral spinal fluid so quickly and efficiently that the brain seems to be defenseless against chemical onslaught. If the brain is so critical to our existence, how is it that the psychoactive substances mentioned above, which are all toxic molecules, can all so easily enter into the inner recesses of the brain and alter its function?

If open country stretched before him, how he would fly, and indeed you might soon hear the magnificent knocking of his fists on your door. But instead, how uselessly he toils; he is still forcing his way through the chambers of the innermost palace; never will he overcome them; and were he to succeed at this, nothing would be gained: he would have to fight his way down the steps; and were he to succeed at this, nothing would be gained: he would have to cross the courtyard and, after the courtyard, the second enclosing outer palace, and again stairways and courtyards, and again a palace, and so on through thousands of years; and if he were to burst out at last through the outermost gate—but it can never, never happen—before him still lies the royal capital, the middle of the world, piled high in its sediment.

— Franz Kafka, “A Message from the Emperor”