A blackout is a phenomenon caused by the intake of alcohol or other substance in which long term memory creation is impaired or there is a complete inability to recall the past. Blackouts are frequently described as having effects similar to that of anterograde amnesia, in which the subject cannot create memories after the event that caused amnesia. 'Blacking out' is not to be confused with the mutually exclusive act of 'passing out', which means loss of consciousness. 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 this is true.[1][2] The negative psychological effects of an alcohol related blackout are often worsened by those who suffer from anxiety disorders.
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Various studies have also proven links between general alcohol consumption and its effects on memory creation.[3] Particularly, these studies have 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.[4]
It is a common misconception that blackouts generally occur only to alcoholics; research suggests that binge drinkers, such as college students, are often at risk as well. In a 2002 survey of college students by researchers at Duke University Medical Center, 40% of those surveyed who had consumed alcohol recently reported having experienced a blackout within the preceding year.[5]
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.[6] 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 such fragmentary blackouts, also known as brownouts, are far more common than en bloc blackouts.[7]
Blackouts are commonly associated with the consumption of large amounts of alcohol; however, surveys of drinkers experiencing blackouts have indicated that they are not directly related to the amount of alcohol consumed. Respondents reported they frequently recalled having "drunk as much or more without memory loss," compared to instances of blacking out.[6] 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.[8]
Memory disruptions by alcohol leading to blackout have been linked to inhibition of long-term potentiation, particularly in the hippocampus, by affecting gamma-Aminobutyric acid (GABA) and N-methyl-D-aspartate neurotransmission (see Effects of alcohol on memory).
Alcohol acts as an agonist of the GABAA type receptor, leading to memory disruption (see Effects of alcohol on memory). Benzodiazepines such as flunitrazepam, midazolam, and alprazolam, and barbiturates such as phenobarbital, which also act as GABAA agonists, are known to cause blackouts as a result of high dose use.
Research indicates that some users of alcohol, particularly those with a history of blackouts, are predisposed to experience blackouts more frequently than others.[9] 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.[10] 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.[11]
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