There are four alternative acute elements, which may indicate the presence of a brain injury; loss of consciousness, a change in mental state, such as being dazed or confused, amnesia or the presence of focal neurological deficits.
Loss of Consciousness in Not Required.
An ongoing misconception about brain injury is that loss of consciousness is necessary for the brain to be injured. Serious researchers have discounted this theory for decades, and as we enter the next millennium, there is really no room left for debate on this issue. Neuropscyhological Assessment, 3rd, by Murial Lezak, has a comprehensive treatment of this subject beginning at page 178: Noting that the concussion syndrome covers a range of symptoms and severity, Gennarelli, (1986) suggests that there are two broad categories of concussion: mild concussion, without loss of consciousness and characterized by symptoms such as seeing stars, if the injury was focal, and or a short period of confusion and disorientation with or without amnesia for a brief time before and or after the event; and classic concussion, defined by reversible coma, occurring at the instant of trauma, which may be accompanied by cardiovascular and pulmonary function changes and neurologic abnormalities …
When the confusion and disorientation resolve within hours or days, the condition is usually considered a mild head injury (see pp. 182-185) although even seemingly mild injuries can have serious neurobehavioral consequences (Gronwall, 1989a) including seizure like symptoms frequently accompanied by chronic cognitive deficits (Verduyn et. al., 1992). The neuropsychological sequelae of concussion without loss of consciousness do not differ in severity from those occurring when there is a brief comatose period ( Leininger, Grambling et al, 1990, Nemeth, 1991) (emphasis added) . In recommending that concussion be defined as “an acceleration/deceleration injury to the head” which is typically but not necessarily accompanied by amnesia, Rutherford (1989) has attempted to extend this diagnosis to the many cases of minor head injury in which behavioral sequelae are consistent with this type of damage, but loss of consciousness in questionable.©Oxford, 1995.
Additional authority that a brain injury can occur without a documented loss of consciousness includes the Sport and Concussion Guidelines, promulgated by the American Academy of Neurology in conjunction with the Brain Injury Association; the Definition of Mild Traumatic Brain Injury, from the American Congress of Rehabilitation Medicine, the treatise, Prognosis of Neurological Disorders, and the treatise Silver, Yudofsky and Hales, The Neuropsychiatry of Traumatic Brain Injury and Greenfield’s Neuropathology.
For more information see http://www.subtlebraininjury.com