Abstract
The capacity to remember self-referential past events relies on the integrity of a distributed neural network. Controversy exists, however, regarding the involvement of specific brain structures for the retrieval of recently experienced versus more distant events. Here, we explored how characteristic patterns of atrophy in neurodegenerative disorders differentially disrupt remote versus recent autobiographical memory. Eleven behavioural-variant frontotemporal dementia, 10 semantic dementia, 15 Alzheimer's disease patients and 14 healthy older Controls completed the Autobiographical Interview. All patient groups displayed significant remote memory impairments relative to Controls. Similarly, recent period retrieval was significantly compromised in behavioural-variant frontotemporal dementia and Alzheimer's disease, yet semantic dementia patients scored in line with Controls. Voxel-based morphometry and diffusion tensor imaging analyses, for all participants combined, were conducted to investigate grey and white matter correlates of remote and recent autobiographical memory retrieval. Neural correlates common to both recent and remote time periods were identified, including the hippocampus, medial prefrontal, and frontopolar cortices, and the forceps minor and left hippocampal portion of the cingulum bundle. Regions exclusively implicated in each time period were also identified. The integrity of the anterior temporal cortices was related to the retrieval of remote memories, whereas the posterior cingulate cortex emerged as a structure significantly associated with recent autobiographical memory retrieval. This study represents the first investigation of the grey and white matter correlates of remote and recent autobiographical memory retrieval in neurodegenerative disorders. Our findings demonstrate the importance of core brain structures, including the medial prefrontal cortex and hippocampus, irrespective of time period, and point towards the contribution of discrete regions in mediating successful retrieval of distant versus recently experienced events.
Highlights
The ability to reminisce on events from the past represents a unique expression of the episodic memory system, and one that is essential for a sense of identity and continuity across subjective time [1]
The recollection of Autobiographical memory (ABM) relies upon the episodic memory system, permitting us to retrieve events from the past that are bound within a unique time and place, for example ‘‘My first holiday abroad with my family.’’ While selfreferential in nature, ABMs contain general conceptual knowledge or semantic memory, derived from the abstraction of content from experiences, for example ‘‘Paris is the capital of France.’’ ABMs necessarily contain episodic and semantic elements [4,5], as well as rich contextual sensory perceptual details and emotional salience, which facilitate the mental reliving of the original event [6,7,8]
The patient groups were matched for disease duration
Summary
The ability to reminisce on events from the past represents a unique expression of the episodic memory system, and one that is essential for a sense of identity and continuity across subjective time [1]. Functional neuroimaging studies in healthy individuals converge to reveal a distributed network of regions subtending successful ABM retrieval This core network includes medial temporal lobe (MTL) structures such as the hippocampus and surrounding parahippocampal cortices, lateral temporal lobe cortices, posterior parietal regions including the posterior cingulate cortex and precuneus, as well as frontal regions such as the medial prefrontal cortex (PFC) [9,10,11]. These studies confirm that coactivation of multiple brain regions must occur to support successful ABM retrieval
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