Artificial grammar learning in Alzheimer's disease

Abstract

Patients with early Alzheimer's disease (AD) exhibit impaired declarative memory although some forms of nondeclarative memory are intact. Performance on perceptual nondeclarative memory tasks is often preserved in AD, whereas conceptual nondeclarative memory is often impaired. A conceptual nondeclarative learning task that has been studied in amnesic patients is the artificial grammar learning (AGL) task. Healthy participants and patients with impaired declarative memory both acquire information about an underlying rule structure in this task and exhibit the ability to identify rule-conforming items, despite the subjective experience of guessing at the response. In this study, 12 patients diagnosed with early AD were tested on the AGL task and a matched recognition task. The patients were able to reliably distinguish rule-conforming items from others, indicating successful AGL. Performance of the AD patients was impaired, relative to controls, on a similar recognition task, although they were found to use information about the grammaticality of study items in an attempt to improve their recognition performance. The AD patients showed a dissociation similar to that seen in anterograde amnesia: impaired recognition memory in conjunction with successful AGL. This finding suggests that the brain areas that support AGL are not compromised early in the course of AD. In addition, the nondeclarative memory of the AD patients acquired during AGL appeared to influence their performance on a declarative memory task, suggesting an interaction between this nondeclarative memory task and declarative memory.