Short term memory describes the ability to recall a small number of events in the recent past that occurred more than a minute before. Most adults have no difficulty recalling such events, but people with certain types of brain damage and dementia lose this ability. They are unable, for example, to recall what day it is or whether someone has been in the same room as them recently. It is always the sign of a serious neurological disorder, but need not be a permanent condition. It is generally limited, depending on the person, to remembering five to nine separate elements. This is one of the reasons telephone numbers are only seven digits long - well within the short term memory of most people.