Blackout (alcohol related amnaesia)

A blackout is a phenomenon caused by the intake of alcohol in which long term memory creation is impaired. Blackouts are frequently described as having effects similar to that of anterograde amnesia. 'Blacking out' is not to be confused with the mutually exclusive act of 'passing out'. Research on alcohol blackouts was begun by E. M. Jellinek in the 1940s. Using data from a survey of Alcoholics Anonymous (AA) members, he came to believe that blackouts would be a good predictor of alcoholism. However, there are conflicting views as to whether or not this is true.

Alcohol and long-term memory
Various studies have proven links between general alcohol consumption and its effects on memory creation. Particularly, these studies had shown that associations made between words and objects when intoxicated are less easily recalled than associations made when not intoxicated. Later blackout-specific studies have indicated that alcohol specifically impairs the brain's ability to take short-term memories and experiences and transfer them to long-term memory. This was shown by the ability to recall associations made while intoxicated being affected over time; it is strongly indicated that memories can be easily recalled for 2-3 minutes before the permanent inability to recall them in the future.

Types of blackouts
Blackouts can generally be divided into two categories, "en bloc" blackouts, and "fragmentary" blackouts. En bloc blackouts are classified by the inability to later recall any memories from the intoxicated period, even when prompted. These blackouts are characterized also by the ability to easily recall things that have occurred within the last 2 minutes, yet inability to recall anything prior to this period. As such, a person experiencing an en bloc blackout may not appear to be doing so, as they can carry on conversations or even manage to accomplish difficult feats. It is difficult to determine the end of this type of blackout as sleep typically occurs before they end. Fragmentary blackouts are characterized by the ability to recall certain events from an intoxicated period, yet be unaware that other memories are missing until reminded of the existence of these 'gaps' in memory. Research indicates that fragmentary blackouts are far more common than en bloc blackouts.

Causes
Blackouts are quite often associated with the consumption of large amounts of alcohol, however surveys of drinkers who have experienced blackouts have indicated that blacking out is not directly related to the amount of alcohol consumed. Respondents reported they frequently recalled having "had drunk as much or more without memory loss," compared to instances of blacking out. Subsequent research has indicated that blackouts are most likely caused by a rapid increase in a person's blood-alcohol concentration. One study, in particular, resulted in subjects being stratified easily into two groups, those who consumed alcohol very quickly, and blacked out, and those who did not black out by drinking alcohol slowly, despite being extremely intoxicated by the end of the study.

Predisposition to blackouts
Research indicates that some users of alcohol, particularly those with a history of blackouts, are predisposed to experience blackouts more frequently than others. One such study indicated a link between prenatal exposure to alcohol and vulnerability towards blackouts, in addition to the oft-cited link between this type of exposure and alcoholism. Alternatively, another study has indicated that there appears to be a genetic predisposition towards blacking out, suggesting that some individuals are made to be susceptible to alcohol related amnesia.