When alcohol is consumed at a rapid rate, the point at which most healthy peoples long-term memory creation starts to fail usually occurs at approximately 0.20% BAC, but can be reached as low as 0.14% BAC for infrequent drinkers. The exact duration of these blackout periods is hard to determine, because most people fall asleep before they end. Upon reaching sobriety, usually after waking, long-term memory creation is completely restored.Chronic alcoholism often leads to a thiamine (vitamin B1) deficiency in the brain, causing Korsakoffs syndrome, a neurological disorder which is generally preceded by an acute neurological condition known as Wernickes encephalopathy (WE). The memory impairment that is pathognomonic to Korsakoffs syndrome predominantly affects the declarative memory, leaving non-declarative memory that is often procedural in nature relatively intact. The disproportionate severity in anterograde episodic memory processes in contrast to other cognitive processes is what differentiates Korsakoff syndrome from other conditions such as alcohol-related dementia. Evidence for the preservation of certain memory processes in the presence of severe anterograde episodic memory serve as experimental paradigm to investigate the components of human memory. Pathophysiology
The pathophysiology of anterograde amnesic syndromes varies with the extent of damage and the regions of the brain that were damaged. The most well-described regions indicated in this disorder are the medial temporal lobe (MTL), basal forebrain, and fornix. Beyond the details described below, the precise process of how we remember – on a micro scale – remains a mystery.
In a case study of a girl who developed anterograde amnesia during childhood, it was determined that the patient ("C.L.") retained semantic memory while having an extreme impairment of episodic memory.One patient, known by the codename "Gene", was involved in a motorcycle accident that damaged significant portions of his frontal and temporal lobes, including his left hippocampus. As a result, he cannot remember any specific episode in his life, such as a train derailment near his house. However, his semantic memory is intact; he remembers that he owns a car and two motorcycles, and he can even remember the names of his classmates in a school photograph. In stark contrast, a woman whose temporal lobes were damaged in the front due to encephalitis lost her semantic memory; she lost her memory of many simple words, historical events, and other trivial information categorized under semantic memory. However, her episodic memory was left intact; she can recall episodes such as her wedding and her fathers death with great detail. Vicari et al. describe that it remains unclear whether neural circuits involved in semantic and episodic memory overlap partially or completely, and this case seems to suggest that the two systems are independent. Both of the patients hippocampal and diencephalic structures on the right and left sides were disconnected. When C.L. came to Vicari et al.s office, her chief complaint was forgetfulness involving both semantic and episodic memory. After administering a battery of neuropsychological tests, Vicari determined that C.L.