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What Is a Concussion? 3 brain whatsoever. It does, however, result in a significant movement or “spin- ning” of the brain at the time of impact. As we shall soon see, it is this rapid movement of the brain that results in a concussion. So what is it that causes a concussion? A concussion is caused by an acceleration of the brain. After the head, face, or other part of the body is struck, the brain is sent spinning in the oppo- site direction. For example, if a basketball player is struck on the left side of the face by the elbow of an opponent, his or her head will accelerate to the right. This rapid movement, or acceleration, of the brain causes it to malfunc- tion. In particular, rotational acceleration or spinning of the brain results in a concussion. There are two main ways to accelerate something. You can push it in a straight line, such that it accelerates in a straight line, away from your pushing hand. This type of acceleration is known as linear acceleration. Imagine a car at a stoplight along a straight road. When the light turns green, the driver steps on the gas. The car starts from a complete stop and accelerates, in a straight line, until the driver reaches a cruising speed at 25–30 miles per hour. This is a form of linear acceleration. Alternatively, you can accelerate something by spinning it. “Spinning” is a more common term for rotational acceleration. When a child takes a toy top or dreidel, places it on a table, and spins it, the child is, in scientific terms, applying a rotational acceleration to the top. It is this rotational type of acceler- ation, when sustained by the human brain, that results in concussion. This has been demonstrated in scientific experiments carried out over the last century. In some sense, it has been known for over 100 years that in order to sustain a concussion, the head has to be free to move. As often happens, this was first realized in the world outside of medicine. This knowledge was commonly used in slaughter houses. In order to prepare various meats for market, the animals must first be killed. This takes place in slaughter houses. It was thought, even 100 years ago, to be inhumane to simply walk up to the animal and kill it. Therefore, men who worked in slaughter houses used to try to stun the animal or knock it unconscious prior to killing it and butchering it in preparation for the market. One common method used to stun the animal was to deliver a concussion by striking it on the head with a bolt. Certainly, if the animal’s head was held in place, preventing it from moving, it would be quite easy to strike it with the bolt. By holding the head still, the butcher could maintain the head in precisely the location where the bolt would be striking from above. Men working in slaughter houses observed, however, that if the animal’s head was held in place, and not free to move after the impact, the animal would not be stunned. It would not be concussed. It would not lose consciousness. But, if the animal was held in place by the shoulders and torso, so that the head was free to move after it was struck by the bolt, the animal would often be concussed it would be dazed, off-balance, and even frankly knocked unconscious. Once the animal was stunned from its concussion, the business of the day could proceed.