Awareness during anesthesia.

MEMORY is not a single entity. Current classification distinguishes between two types: explicit, or conscious memory, and implicit, or unconscious memory. Explicit memory refers to the conscious recollection of previous experiences. Implicit memory, by contrast, refers to changes in performance or behavior that are produced by previous experiences but without any conscious recollection of those experiences.’ Explicit memory is equivalent to “remembering” (e.g., can you remember what you did last Tuesday evening?). In the case of an anesthetized patient, one might ask the patient in the postoperative period “can you remember hearing any words or sounds during your operation?” (i.e., a recall test) or “which of the following words were played to you during surgery?” (a recognition test). As an example of implicit memory, consider the following scenario. Patients were exposed during anesthesia to a list of words containing the word “pension. ” Postoperatively, when they were presented with the three-letter word stem “PEN-” and were asked to supply the first word that came to their minds beginning with those letters, they gave the word “pension” more often than “pencil” or “peninsula” or others. The term “awareness” will be used to describe explicit memory during anesthesia.