Provoked confabulations distinguish patients with early Alzheimer's disease from normal elderly
The initial experiment used a new ABM questionnaire to test the ability of a group of 21 elderly adults and 20 patients with minimal to mild AD to retrieve personal episodic and semantic memories from across the life span. The test revealed that AD patients were significantly impaired compared to elderly adults on all aspects of the questionnaire compared to controls, especially for the retrieval of ‘true’ episodic memory, which was defined as uniquely detailed information that enables one to re-experience an event. There was a significant temporal gradient in retrieval of semantic memory but not for episodic memory. The results suggested that there was a dissociation between episodic and semantic ABM. The neural segregation of the episodic and semantic aspects of ABM was then explored using a paradigm based on the questionnaire during fMRI scanning. Twelve elderly and eleven young adults were tested. The results suggested that retrieval of the episodic aspect was linked to activation in the regions of the right frontal lobe, whereas retrieval of the semantic aspect was associated with activation of left frontal lobe areas. Elderly participants showed a decrease in activation of the right frontal lobe region during episodic retrieval compared to younger adults. The proposal that this area could be linked to autobiographical delusions was then explored. A new test that comprised of a discursive and a questionnaire section that could provoke confabulation revealed that AD patients made significantly more confabulations on both sections of the test than elderly adults. Through a series of experiments, it was found that the confabulation produced was not due to an overload in the memory capacity of AD patients or due to executive or attentional deficits. Rather it was found that the tendency to confabulate was linked to a deficit in the retrieval of the episodic aspect of ABM. Thus, the results from the experiments suggest that memory distortions in ABM in AD could be linked to a deficit in episodic memory and impaired reality monitoring, due to dysfunction of regions of the right frontal lobe.