Implicit learning in patients with Alzheimer's disease.

We examined implicit memory using priming and procedural learning tasks in patients with probable Dementia-Alzheimer's Type (DAT) to examine whether priming and procedural processes could be dissociated and whether task specificity was a factor in DAT patient performance. Priming was tested using a word recognition paradigm (perceptual priming) and by repeated administrations of a fragmented objects test (long term priming). Procedural learning was tested using repeated and random sequences on a choice serial reaction time task and by repeated administration of a puzzle map of the United States. DAT patients were compared to hospitalized depressed patients, patients suffering from Progressive Supranuclear Palsy (PSP), and normal controls. We found that DAT patients demonstrated marginal but significant implicit learning on both procedural learning and perceptual priming tasks. DAT patients performed relatively better on the procedural learning task than a perceptual priming task compared to PSP patients, suggesting that priming of meaningful stimuli is subserved by cortical structures whereas procedural motor responses to simple serial visual stimulus patterns can be maintained by subcortical systems. Furthermore, our findings suggest that priming and procedural processes can be dissociated and that task specificity is a factor in interpreting the results of implicit learning paradigms in DAT patients. The implications of these results for models of knowledge representation and memory processes as well as the way they can serve as models for testing nootropic drug effects are discussed.