Ask A Scientist

How many brain cells do you lose when you bang your head into something and does it make you any stupider?

Asked by: Brianna Carey
School: Maine Endwell Middle School
Grade: 6
Teacher: Mr. Wagstaff
Hobbies/Interests: Gymnastics
Career Interest: Veterinarian

Answer from Ralph Miller

Distinguished Professor of Psychology, Binghamton Univeristy

PhD school: Rutgers University, New Brunswick NJ
Family: Wife: Joan; Two children: Neal and David
Hobbies/interests: Hiking, bicycling, listening to music, fund raising for the Cider Mill Playhouse, serious eating and drinking
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The human brain "floats" inside the skull and is cushioned by surrounding membranes and cerebrospinal fluid.  This cushion protects the brain rather well from minor blows.  But forceful blows can cause the brain to bounce against the inner wall of the skull resulting in the tearing of blood vessels, pulling of neural connections, and bruising of the brain.  This is called a brain concussion.  If a concussion is severe enough, the brain can swell and blood flow may be reduced so that the brain cells do not get enough oxygen and nutrients.  Severe blows to the head can cause death of brain cells (neurons) and can sever the delicate connections between neurons.  In fact the severing of connections is a major factor in causing neurons to die.  Neurons with inadequate connections to other neurons are at increased risk of dying.  How many neurons die certainly depends on how hard you bang your head and on how frequently it happens.  Another important factor is exactly where on your head you are hit.  There are considerable data showing that frequent or hard blows to the head can reduce intelligence and that this reduction in cognitive skills is directly related to how many neurons die.  The intelligence of boxers and people who play contact sports is at considerable risk from the many hard blows to the head that these individuals receive.  A few mild blows to the head (which we all experience) likely do not result in any enduring loss of intelligence, at least to the degree that we can measure.  But a single severe blow to the head might cause temporary and sometimes even permanent confusion, memory impairment, reduced ability to plan, and a decrease in attention so that a person is easily distracted and unable to focus on a task, follow directions, or understand information.  The brain is a fragile organ that is best not banged at all if one can possibly avoid it.  Some species of animals that commonly bang their heads, such as woodpeckers, have special shock absorbers inside their skulls around their brains to cushion the impact of the blows.  The brains of humans have some degree of protection, but are nowhere as well protected as are the brains of woodpeckers.  Wearing proper protective gear (like a helmet) is strongly recommended when engaged in sports that create a risk of a blow to the head (for example, boxing, wrestling, football, baseball, softball, bicycling, hockey, roller skating, skateboarding, horseback riding, skiing, and using powered recreational vehicles).  Severe blows to the head can not only lower intelligence, but can also interfere with control of one's muscles, producing tremors that resemble Parkinson's Disease.  Evolution has given us brains that can do amazing things.  It would be most unwise to intentionally do anything that could cause injury to one's brain.

Last Updated: 3/1/17