Dissociation of implicit memory in dementia: Neurological implications

Abstract

Lexical and pictorial priming tasks as well as tests of motor skill learning and weight biasing were administered to patients in the early stages of Alzheimer’s Disease (AD) and Huntington’s Disease (HD) and to intact control subjects. Lexical priming was evaluated with a stem-completion and a paired-associate paradigm, and perceptual priming was measured with a task involving the identification of fragmented drawings of common objects. A pursuit-rotor task was used to assess motor skill learning. Although both patient groups were severely impaired on explicit memory tasks, they exhibited marked dissociations on the implicit tests. The AD patients showed little lexical and pictorial priming, but performed like the control subjects on the weight-biasing and pursuit-rotor tasks. In contrast, the HD patients were unable to acquire the pursuit-rotor skill and demonstrated little weight biasing while performing like the control subjects on the lexical and pictorial priming tasks. These findings indicate that different forms of implicit memory may depend upon distinct constellations of brain structures. The integrity of the association cortices affected in AD may be necessary for the maintenance of lexical and pictorial priming, whereas the basal ganglia damaged in HD may be critical for the development of the motor programs underlying skill learning and weight biasing. © 1990, The Psychonomic Soceity, Inc.. All rights reserved.