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-reversed view and to retain that skill over 24-h 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.