Blackout (alcohol-related Amnesia) - Types of Blackouts

Types of Blackouts

Blackouts can generally be divided into 2 categories, "en bloc" blackouts and "fragmentary" blackouts. En bloc blackouts are classified by the inability to later recall any memories from the intoxication 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 such fragmentary blackouts, also known as brownouts, are far more common than en bloc blackouts. Memory impairment during acute intoxication involves dysfunction of episodic memory, a type of memory encoded with spatial and social context. Recent studies have shown that there are multiple memory systems supported by discrete brain regions, and the acute effects of alcohol and learning and memory may result from alteration of the hippocampus and related structures on a cellular level. A rapid increase in blood alcohol concentration (BAC) is most consistently associated with the likelihood of a blackout. However, not all subjects experience blackouts which implies genetic factors play a role in determining CNS vulnerability to the effects of alcohol. This may predispose an individual to alcoholism, as altered memory function during intoxication may affect an individual’s alcohol expectancy, one may perceive positive aspects of intoxication while unintentionally ignoring the negative aspects.