Neurology Central

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


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:

  • What is the mechanism of concussion? Common symptoms associated with concussion include rapidly resolving loss of consciousness, headache, confusion, memory impairment, attention and executive function, sense of dizziness, imbalance, sleep disturbances and behavioral changes.

  • What is the mechanism of recovery from concussion? Most commonly, concussive symptoms improve over a period of hours, days or weeks. In some patients, however, symptoms persist, known as postconcussive syndrome.

  • What are the longer-term or even permanent effects of repeated concussion? Repeated concussion presents other problems: more prolonged recovery period with subsequent concussions, and the risk of a delayed neurodegenerative disorder call chronic traumatic encephalopathy (CTE). In addition, a rare condition has been described in which fatal or near-fatal, rapid onset, brain swelling occurs with concussion. It has been questioned whether the latter occurs due to a second concussion occurring before the brain’s autoregulation of blood flow has recovered from a preceding concussion, so-called ‘second hit’ phenomenon.

Most of the key questions in these three areas of concussion research remain to be solved. We know little of the underlying mechanisms and pathophysiology of concussion and postconcussive syndrome, as well as the vulnerability and mechanisms of CTE.