Fragmentary blackouts are characterized by a person having the ability to recall certain events from an intoxicated period, and yet being unaware that other memories are missing until reminded of the existence of those 'gaps' in memory. Research indicates that such fragmentary blackouts, also known as brownouts, are far more common than en bloc blackouts.[9] 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.