Amnesia is a term describing a group of disorders involving partial or total inability to remember past experiences. One of the more common types of amnesia occurs after head trauma.
Amnesia is said to be retrograde when the memory loss is for events prior to the injury.
It is anterograde when the loss is for events after the injury. Head trauma may result in one or both types. Many aging persons gradually develop noticeable difficulties in memory, at first for names, then for events, and sometimes even occasionally for spatial relationships. This widely experienced, so-called benign forgetfulness bears no proven relationship to degenerative dementia, but may be a forewarning, since some similarities are hard to overlook. Transient global amnesia is the sudden appearance of severe, forgetful confusion lasting from as little as 30 to 60 min to as long as 12 hours or more.