The role of hippocampus in the retrieval of autobiographical memories in patients with amnestic Mild Cognitive Impairment due to Alzheimer's disease

Abstract

The role of the hippocampus and neocortical areas in the retrieval of past memories in pre‐dementia Alzheimer's disease (AD) patients was investigated. The aim was to assess whether the hippocampus has a temporary role in memory trace formation, according to the Cortical Reallocation Theory (CRT), or whether it continuously updates and enriches memories, according to the Multiple Trace Theory. According to the former theory, hippocampal damage should affect more recent memories, whereas the association cortex is expected to affect memories of the entire lifespan. In the second case, damage to either the hippocampus or the association cortices should affect memories of the entire lifespan. Seventeen patients with amnestic Mild Cognitive Impairment due to AD were submitted to autobiographical (i.e., episodic and semantic personal) memory assessment. Patients underwent MRI for the acquisition of T1‐weighted brain volumes. Voxel‐based morphometry was used to assess correlations between grey matter (GM) volumes and autobiographical memory. Correlation analyses revealed a strict association between GM volumes in the hippocampus and patients’ ability to retrieve the most recent but not the oldest autobiographical memories in both aspects, episodic and semantic. Moreover, patients’ GM volumes in the pre‐frontal and temporal polar areas were associated with recollection of episodic and semantic events, respectively. Finally, GM volumes in the precuneus and occipital cortex were associated with retrieval of the most recent episodic events. These findings indicate that the hippocampus has a specific time‐dependent role; thus, they support the CRT.

Altered Time Awareness in Dementia

“…Moreover, the hippocampus is critical for initial encoding of events and their embedding in emotional context (3,19,20,95), and the anterior temporal lobe is likely to be important for the semantic integration of autobiographical events (96). The integrity (or partial integrity) of these brain areas might plausibly support a tendency to re-live past autobiographical events, in line with previous evidence in neurodegenerative syndromes (97)(98)(99).…”

Anomalies of Autobiographical Memory

“…Across all 40 patients, the correlation with medial temporal volume was r = .42, p < .05; and in 14 patients whose primary pathology was in the medial temporal lobes (or 'hippocampal complex', see p. 880 of that paper), it was only r = .28 and not significant. Other investigators have also found that the degree of autobiographical episodic impairment is not closely correlated with the severity of hippocampal atrophy (Serra et al, 2018;Tomadesso et al, 2015). In a recent review, Sekeres, Winocur, and Moscovitch (2018) concluded the same, but postulated specialisation in subfields along the long axis of the hippocampi.…”

Altered Directed Functional Connectivity of the Hippocampus in Mild Cognitive Impairment and Alzheimer’s Disease: A Resting-State fMRI Study

“…Various neuroimaging studies have demonstrated abnormal structure and function of the hippocampus in patients with AD and MCI. β-Amyloid abnormalities and tau pathology in the preclinical stages of AD initially appear in the hippocampus (Braak and Braak, 1991; Hanseeuw et al, 2016; Serra et al, 2018). Longitudinal studies have shown significant volume loss in the hippocampus during the progression of AD, and there is a direct relationship with cognitive decline (Everitt and Dunn, 2013; Joko et al, 2016).…”