Summary and conclusions
       As detailed in this brief review, alcohol can have a dramatic impact on memory. Alcohol primarily disrupts the ability to form new long-term memories; it causes less disruption of recall of previously established long-term memories or of the ability to keep new information active in short-term memory for a few seconds or more. At low doses, the impairments produced by alcohol are often subtle, though they are detectable in controlled conditions. As the amount of alcohol consumed increases, so does the magnitude of the memory impairments. Large quantities of alcohol, particularly if consumed rapidly, can produce a blackout, an interval of time for which the intoxicated person cannot recall key details of events, or even entire events. En bloc blackouts are stretches of time for which the person has no memory whatsoever. Fragmentary blackouts are episodes for which the drinker's memory is spotty, with "islands" of memory providing some insight into what transpired, and for which more recall is usually possible if the drinker is cued by others. Blackouts are much more common among social drinkers than previously assumed and should be viewed as a potential consequence of acute intoxication regardless of age or whether one is clinically dependent upon alcohol.
       Tremendous progress has been made toward an understanding of the mechanisms underlying alcohol-induced memory impairments. Alcohol disrupts activity in the hippocampus via several routes-directly, through effects on hippocampal circuitry, and indirectly, through interactions between the hippocampus and other brain regions. The impact of alcohol on the frontal lobes remains poorly understood, but likely plays an important role in alcohol-induced memory impairments.
       Modern neuroimaging techniques, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), provide incredible opportunities for investigating the impact of drugs like alcohol on brain function during the performance of cognitive tasks. The use of these techniques will no doubt yield important information regarding the mechanisms underlying alcohol-induced memory impairments in the coming years. Memory formation and retrieval are highly influenced by factors such as attention and motivation (e.g., Kensinger et al. 2003). With the aid of neuroimaging techniques, researchers may be able to examine the impact of alcohol on brain activity related to these factors, and then determine how alcohol contributes to memory impairments.
       Despite advances in human neuroimaging techniques, animal models remain absolutely essential in the study of mechanisms underlying alcohol-induced memory impairments. Hopefully, future work will reveal more regarding the ways in which the effects of alcohol on multiple transmitter systems interact to disrupt memory formation. Similarly, recent advances in electrophysiological recording techniques, which allow for recordings from hundreds of individual cells in several brain regions simultaneously (Kralik et al. 2001), will hopefully provide much needed information regarding the impact of alcohol on the interactions between disparate brain regions involved in the encoding, storage, and retrieval of information.