CONCUSSION   [ back to Glossary Index ]
Concussion refers to closed head cerebral trauma (from blunt impact to the head or rapid acceleration- deceleration of the head) which causes a physiologic disruption of brain function associated with violent shaking or bouncing of the brain within the rigid skullcase. In March 1997 the American Academy of Neurology adopted a scale for grading concussions in the context of contact sports such s football. Grade I concussion involves dazing or confusion with no loss of consciousness lasting less than 15 minutes. Grade II concussion involves dazing or confusion for more than 15 minutes with no loss of consciousness. A Grade III concussion involves any period of loss of consciousness. Thus, concussion may or may not involve a loss of consciousness. However, it does require PTA (post-traumatic amnesia). In a Grade I concussion the PTA may be limited to just seconds. A severe concussion can cause weeks or even months of PTA.   The AAN has not graded severe concussions. Back in 1982 Teasdale and Jennett developed the Glasgow Coma Scale to assess the risk of death and need for neurosurgical intervention in concussed patients, with mild being 13-15, moderate 9-12 and severe 3-8. The terms "mild traumatic brain injury" refers to a concussion involving evident alteration of mental status (such as dazing or confusion), 0-20 minutes of loss of consciousness,  less than 24 hours of PTA and a GCS score of 13-15. 

Many but not all people who suffer a concussion go on to suffer from Post-Concussion Syndrome (PCS). See below. Concussion is not the only form of traumatic brain injury. Open head wounds from a bullet, knife or other projectile can cause severe brain injury, often without a loss of consciousness, the  most famous example being Phinneas Gage, the blasting foreman of the Burlington, Vermont railroad. During the 1840s Gage was unlucky enough to drop his 3 foot iron tamping rod near a dynamite cap, which exploded from the spark, and sailed through his cheek, up through his frontal lobes, up through and out of the top of his skull and landed nearby with scraps of scalp, skull and brain on it.  Gage never lost consciousness, and was able to answer all of the town doctor's questions as he peered through the gaping hole atop Gage's head down into his brain. Gage survived the ordeal for another five years, before succumbing to epileptic seizures. Those five years were a textbook example of orbito-frontal brain injury. Gage went from being a punctual, responsible and reliable person to someone who drank, swore at and had fist fights with his co-workers. How could this have happened?

We now know that the tissue of the brain contains no pain sensing nerve fibers (so the hole in his brain caused him no pain); that loss of consciousness requires traumatic compression or stretching of the brainstem at the base of the skull (so damage purely localized to the frontal area would not knock him out); and that damage to the frontal lobe area directly behind the eyes takes away much of a person's ability to control his own impulses and his anger. Gage will always stand as the best counter-example to the false statement that TBI cannot occur in the absence of a loss of consciousness.