People with Korsakoff Syndrome usually have profound deficits in their ability to recall recent events, or in what is termed their "explicit memory." Researchers at Stanford University School of Medicine found that individuals with Korsakoff Syndrome retain the ability to learn information presented visually, even without a conscious recollection of that learning.
"'Explicit events' refer to situations that an individual can consciously recall when asked, 'what did you do yesterday?' or 'what did you do over the holidays?,'" explained Edith Sullivan, a professor in the department of psychiatry and behavioral sciences at Stanford University School of Medicine and corresponding author for the study. "Individuals with Korsakoff Syndrome cannot consciously recall what they did or information presented to them earlier in the day."
"Explicit memory is often referred to as 'knowing what' and implicit memory to 'knowing how,'" said Sara Jo Nixon, professor and director of the Neurocognitive Laboratory at the University of Kentucky. "However, the impact of chronic excessive alcohol consumption on implicit memory has been less clear and less frequently studied. Visuoperceptual tasks likely engage a significant component linked to implicit memory functions. Thus, examining implicit memory using such a task in a comparison of Korsakoff alcoholics, non-Korsakoff alcoholics and controls is an effective way of disentangling alcohol's long-term effects on 'knowing how' versus 'knowing what.'
"These distinctions are important in considering the process of recovery of function and in identifying brain areas which may be particularly vulnerable to the neurotoxic effects of alcohol." "Day-to-day examples of visuoperceptual learning," added Sullivan, "would be the ability to recognize or recall faces or objects seen previously, or the ability to navigate to a destination after having done so previously."
Sullivan gave the "Gollin Incomplete Pictures Test" to four groups of men -- those with Korsakoff Syndrome, recently detoxified alcoholics without Korsakoff Syndrome, and two groups of controls, one of age-matched men and another of young men.
Memory Not a Unitary ProcessBoth alcoholic groups showed impairments in their visuoperceptual ability. However, all the men in the study, even those with Korsakoff Syndrome, demonstrated visuoperceptual learning. "The Korsakoff Syndrome group showed additional learning after continued exposure to the stimuli, despite initial visuospatial deficits and profound explicit memory impairment," according to a news release.
"We found that individuals with Korsakoff Syndrome are able to learn information presented visually, even though they had no conscious recollection of that learning," said Sullivan. "In other words, their behavior shows that learning occurred even though they do not remember having performed the test previously. These findings demonstrate that memory is not a unitary process, but instead consists of a number of different processes and underlying neurological systems.
Relatively Unimipaired Memory Processes"Some, such as conscious declarative memory for newly acquired events, are disrupted in individuals with Korsakoff Syndrome, whereas others, such as visuospatial implicit learning, are spared."
"The findings of the study and their implications are intriguing," added Nixon. "Although learning the task was more difficult for the alcoholics, once learned, their implicit memory processes were relatively unimpaired. The brain areas associated with implicit memory that appear to be relatively spared in chronic alcoholism involve primarily posterior cortical areas."
Continued to Show Learning"This study is consistent with previous studies demonstrating implicit memory processes in Korsakoff Syndrome," said Sullivan, "and expands on previous studies by demonstrating that Korsakoff Syndrome individuals continue to show learning after continued exposure of the information. That is, learning was not only retained after one day, but was enhanced when the subject was presented with the information again."
Nixon said the study's findings "illustrate that not all types of 'memory' are equally affected and that, indeed, certain fundamental memory functions may be intact even when clinically relevant memory dysfunction exists. These intact functions may provide a foundation for longer-term recovery, at least in non-Korsakoff patients."
Source: Sullivan's study was published in the April 2006 issue of Alcoholism: Clinical & Experimental Research.