Word frequency and word stem completion in Korsakoff patients.

Korsakoff patients are generally agreed to be impaired in conscious recollection, but whether their implicit memory performance is also affected is less certain. A deficit in novelty dependent encoding (i.e., elaboration learning) could account for both types of impairments and predicts a reduced implicit word frequency effect in the patients. This effect was examined with word stem completion in nineteen Korsakoff patients and nineteen healthy controls. The word frequency effect was larger in controls than in patients in absolute terms, but not reliably so. It is concluded that elaboration learning may be spared to some degree in Korsakoff amnesia, but, in line with the original reasoning by Korsakoff (1889/1996), it may only be engaged by the patients when they are continuously prompted to do so.

Dependence of explicit and implicit memory on hypnotic state in trauma patients.

BACKGROUND: It is still unclear whether memory of intraoperative events results entirely from moments of inadequate anesthesia. The current study was designed to determine whether the probability of memory declines with increasing depth of the hypnotic state. METHOD: A list of words was played via headphones during surgery to patients who had suffered acute trauma. Several commonly used indicators of anesthetic effect, including the bispectral index, were recorded during word presentation. First, these indicators served as predictors of the memory performance in a postoperative word stem completion test. Second, general memory performance observed in the first part was separated into explicit and implicit memory using the process dissociation procedure, and then two models of memory were compared: One model assumed that the probability of explicit and implicit memory decreases with increasing depth of hypnotic state (individual differences model), whereas the other assumed equal memory performance for all patients regardless of their level of hypnotic state. RESULTS: General memory performance declined with decreasing bispectral index values. None of the other indicators of hypnotic state were related to general memory performance. Memory was still significant at bispectral index levels between 60 and 40. A comparison of the two models of memory resulted in a better fit of the individual differences model, thus providing evidence of a dependence of explicit and implicit memory on the hypnotic state. Quantification of explicit and implicit memory revealed a significant implicit but no reliable explicit memory performance. CONCLUSIONS: This study clearly indicates that memory is related to the depth of hypnosis. The observed memory performance should be interpreted in terms of implicit memory. Auditory information processing occurred at bispectral index levels between 60 and 40.