Concussion, from the Latin concutere ("to shake violently") or the Latin concussus ("action of striking together"), is the most common type of traumatic brain injury. The terms mild brain injury, mild traumatic brain injury (MTBI), mild head injury (MHI), minor head trauma, and concussion may be used interchangeably, although the last is often treated as a narrower category. The term "concussion" has been used for centuries and is still commonly used in sports medicine, while "MTBI" is a technical term used more commonly nowadays in general medical contexts. Frequently defined as a head injury with a temporary loss of brain function, concussion can cause a variety of physical, cognitive, and emotional symptoms.

Treatment of concussion involves monitoring and rest. Rest includes both physical and cognitive rest (including going easy on such activities as school work, television watching and text messaging). Symptoms usually go away entirely within three weeks, though they may persist, or complications may occur.

People who have had one concussion seem to be more susceptible to another, especially if the new injury occurs before symptoms from the previous concussion have completely gone away. There is also a negative progressive process if smaller impacts cause the same symptom severity. Repeated concussions may increase a person's risk in later life for dementia, Parkinson's disease, and/or depression.

Concussions have a variety of signs including somatic (such as headache), cognitive (such as feeling in a fog), emotional (such as emotional changeability), physical signs (such as loss of consciousness or amnesia), behavioral changes (such as irritability), cognitive impairment (such as slowed reaction times), and/or sleep disturbances. A 2010 Pediatrics review article regarding sports-related concussions in both children and adolescents noted that fewer than 10% of sports-related concussions had the symptom of loss of consciousness.

Due to factors such as widely varying definitions and possible underreporting of concussion, the rate at which it occurs annually is not known; however it may be more than 6 per 1,000 people. Common causes include sports injuries, bicycle accidents, car accidents, and falls; the latter two are the most frequent causes among adults. Concussion may be caused by a blow to the head, or by acceleration forces without a direct impact. The forces involved disrupt cellular processes in the brain for days or weeks. On the battlefield, MTBI is a potential consequence of nearby explosions.

It is not known whether the concussed brain is structurally damaged the way it is in other types of brain injury (albeit to a lesser extent) or whether concussion mainly entails a loss of function with physiological but not structural changes. Cellular damage has reportedly been found in concussed brains, but it may have been due to artifacts from the studies. It is now thought that structural and psychiatric factors may both be responsible for the effects of concussion.

Read more about Concussion:  Classification, Signs and Symptoms, Mechanism, Diagnosis, Prevention, Treatment, Prognosis, Epidemiology, History