AMNESIA   [ back to Glossary Index ]
Amnesia is the inability to remember learned information. TBI can cause retrograde amnesia (loss of recall of events right before the trauma) and/or anterograde amnesia (loss of recall of events for some period of time after the trauma). Another term for anterograde amnesia is post-traumatic amnesia or PTA. This refers to the period following brain trauma when the victim is unable to effectively imprint and retain a stable, continuous memory of events. For example, after leaving the hospital a person who was in coma is never able to recall awakening from coma, being examined by and speaking to doctors or going through physical therapy in the hospital before his discharge. There are some chronic neurologic conditions (including epilepsy, Wernicke-Karsokoff's from severe alcoholism and certain forms of migraine) which produce episodes of total memory blackout called Transient Global Amnesia. 
The duration of PTA and duration of loss of consciousness following brain trauma are commonly used by physicians as yardsticks to classify a TBI as mild, moderate or severe. Without exception, the longer the duration of a patient's period of PTA, the the more severe his traumatic brain injury and the worse his final neurospyschological outcome following recovery. With coma the prognosis for a decent recovery grows increasingly grim between the 3rd and 6th month, yet coma presents a more irregular, tricky situation than PTA, because of the number of patients who wake from a lengthy period of coma, and shock their doctors by returning to good levels of functioning.