How easy is it to knock someone out with a smack to the back of the head? What causes a person to lose consciousness?

May 5, 2006

Dear Cecil:

After watching countless spy movies, westerns, and TV cop shows, I wonder: how easy is it to knock someone out by smacking them on the back of the head with a pistol, club, etc? Since I'm not willing to act as a test subject, although I'm pretty sure I'd have plenty of volunteers willing to do the smacking, I'm asking you as the next-best source. --Dave Arnold, Ashland, Kansas

I was wondering: When you get hit in the head really hard, you get knocked out. Why? What causes a person to lose consciousness? This is probably gonna be a tough one.

Could be. See what you make of this:

Immediately after biomechanical injury to the brain, abrupt, indiscriminant release of neurotransmitters and unchecked ionic fluxes occur. The binding of excitatory transmitters, such as glutamate, to the N-methyl-D-aspartate (NMDA) receptor leads to further neuronal depolarization with efflux of potassium and influx of calcium. These ionic shifts lead to acute and subacute changes in cellular physiology.

After two more paragraphs in this vein, the authors (Giza and Hovda, 2001) remark, "This overview represents a simplified framework of the neurometabolic cascade [involved in a knockout]." They then launch into the non-dumbed-down version. I get the drift, but the average reader is apt to think he just got hit on the head.

Is there a simpler explanation? Sorta, but be warned--nobody really understands what causes a concussion, as a knockout is more properly known. (Just so we're clear, what sports types call a "ding," in which you're stunned but conscious, is a mild concussion.) A few basics: First, sudden acceleration or deceleration of the head seems to be essential. If somebody clouts you from above, so that your head remains stationary, you may suffer other injuries but probably no knockout. Second, strong evidence suggests that a KO requires twisting or rotational motion--one reason woodpeckers don't beat themselves silly, it's thought, is that their bills travel straight back and forth, like a jackhammer. In contrast, a boxer loses consciousness when a blow causes his brain to slosh and spin inside the skull.

Is knocking somebody out as easy as it looks on TV? If we're talking Tweety pounding Sylvester atop the noggin with a mallet, no, that's not how it works. A compact, head-snapping shot to the side of the jaw, on the other hand, might well do the trick.

This brings us back to the central question: How is it that a single blow can cause somebody to black out only to revive without apparent permanent damage (although see below)? In a 2002 review, New Zealand physiologist Nigel Shaw rules out some of the more common theories--for example, that you lose consciousness because disrupted blood flow starves your brain of oxygen. Not possible: blood flow is just too poky to account for the near instantaneousness of a classic knockout. More likely, Shaw thinks, a concussion is a form of epileptic seizure involving massive, uncontrolled brain-cell discharge--that's where Giza and Hovda above seem to be going with their talk of indiscriminant neurotransmitter release.

But the convulsion theory doesn't explain everything. Consider the sad fate of countless professional boxers, most prominently Muhammad Ali but also Jack Dempsey, Joe Louis, and many others. All suffer or suffered from a condition variously called pugilistic Parkinson's syndrome, punch-drunk syndrome, or chronic traumatic encephalopathy (CTE), characterized by tremors, rigidity, slurred speech, and a halting gait. Studies have shown that as many as 18 percent of professional boxers develop CTE, and that the more bouts they fight, the worse they end up.

A distinction is sometimes drawn between Parkinson's syndrome, which is caused by repeated head trauma, and the clinically similar but more common Parkinson's disease, the cause of which is unknown but presumably doesn't involve getting regularly beat up. Ali's doctors over the years have disagreed about whether the champ has the disease or the syndrome. Evidence for the former includes the fact that his condition has worsened even though he retired from the ring long ago; for the latter that, come on, the guy was a boxer. Ali suffered only one professional knockout (and a technical one at that), in 1980 against Larry Holmes, to my mind suggesting that, contrary to what many coaches think, getting your bell rung a few times too many can be as bad as knockouts over the long haul. To further complicate matters, research suggests CTE is most likely to emerge in boxers with a particular gene--some veteran fighters (George Foreman and Max Schmeling are two I've seen mentioned) don't develop the problem.

So we've got an epilepsy connection, a Parkinson's connection, and I didn't even mention the Alzheimer's connection. Not to give you the old rope-a-dope, but where the brain is concerned, what we know is far exceeded by what we don't.

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