Concussion research at the National Institutes of Health: an update from the National Institute of Neurological Disorders and Stroke

Concussion: the scope of the issue Concussion is an exceedingly common type of traumatic brain injury (TBI), yet little is known about what happens to the brain at the time of concussion. A concussion can be defined as a sudden onset change in neurologic function that occurs immediately after the brain encounters a mechanical force. When the head sustains an injury, direct or rotational biomechanical forces induce physiologic dysfunction; the most characteristic is immediate loss or alteration of consciousness. Each year, between 1.6 and 3.8 million sports-related concussions occur in the USA, particularly in youth athletes [1]. In the US military, it is estimated that roughly 20% of the deployed forces suffered a head injury in the wars in Iraq and Afghanistan, 83% of whom endured a mild, uncomplicated TBI or concussion [2]. While striking, these figures are likely vast underestimates of the actual number of afflicted individuals, since many who suffer concussion do not seek medical attention. The issues surrounding concussion can be divided into three major areas: