Exploring the Domain Specificity and the Neural Correlates of Memory Unawareness in Alzheimer's disease

Patients with Alzheimer’s disease are less accurate than controls to predict their episodic performance, but they are as accurate as controls to predict their semantic performance. However, the dissociation between episodic and semantic metamemory had never been tested directly in the same patients. This study aimed to explore the dissociation between episodic and semantic metamemory in Alzheimer’s disease using the feeling-of-knowing paradigm. In addition, we investigated the link between memory awareness and resting-state cerebral glucose metabolism and gray matter density, in episodic and semantic tasks independently. Data from 50 patients with Alzheimer’s disease were compared to data from 30 healthy controls. Results showed that patients with Alzheimer’s disease had more difficulties to predict their recognition in the episodic task than in the semantic task, while this difference was smaller in controls. Lack of awareness in the episodic task was associated with hypometabolism in right frontoparietal areas in patients with Alzheimer’s disease. These results support the idea of a dissociation between episodic and semantic metamemory in Alzheimer’s disease.