The blow that causes a concussion is usually sudden and forceful—a fall to the ground, a punch to the head, a motor vehicle accident. Also, such a blow sometimes results from child abuse. Whatever the cause, the resulting injury is mild compared with the damage done by cerebral contusions or lacerations.

Concussion may produce a short-term loss of consciousness, vomiting, and both anterograde and retrograde amnesia, in which the patient not only can’t recall what happened immediately after the injury but also has difficulty recalling events that led up to the traumatic incident. The presence of anterograde amnesia and the duration of retrograde amnesia reliably correlate with the severity of the injury.