Intact acquisition and long-term retention of mirror-tracing skill in Alzheimer's disease and in global amnesia.
The ability of patients with Alzheimer's disease (AD) or global amnesia (AMN) to acquire skill for tracing a pattern seen in mirror-revers ed view and to retain that skill over 24-hr intervals was examined. Both patient groups had poor recall and recognition of their mirror-tracing experience, but they acquired and retained mirror-tracing skill as well as normal control subjects. One AMN patient (H.M.) retained the skill over a year-long interval. Furthermore, the patients transferred their skill normally to an alternate pattern. These results indicate that the memory system underlying mirror-tracing skill learning is separable from medial-temporal structures compromised in AMN and AD and from neocortical areas compromised in AD. Brain regions relatively spared in early AD, such as the basal ganglia or cerebellum, may mediate critical aspects of the learning of novel sensorimotor associations that underlie skilled mirror tracing. Alzheimer's disease (AD) is an age-related neurodegenerative disorder that impairs many domains of cognition, especially the learning of new information. AD patients have impaired recall and recognition of materials or experiences even after delays as short as a few seconds (e.g., Corkin, 1982). Experimental examinations of learning in AD patients, however, have revealed intact memory for certain kinds of experience in at least three domains. One domain is that of perceptual aftereffects such as the McCollough effect (Savoy & Gabrieli, 1991). A second domain consists of some kinds of repetition priming, in which learning is measured as a change in the processing of a stimulus because of prior exposure to that stimulus (e.g., Gabrieli et al., 1992, in press; Keane, Gabrieli, Fennema, Growdon, & Corkin, 1991).