Scene construction impairments in Alzheimer's disease – A unique role for the posterior cingulate cortex

Abstract

Episodic memory dysfunction represents one of the most prominent and characteristic clinical features of patients with Alzheimer's disease (AD), attributable to the degeneration of medial temporal and posterior parietal regions of the brain. Recent studies have demonstrated marked impairments in the ability to envisage personally relevant events in the future in AD.It remains unclear, however, whether AD patients can imagine fictitious scenes free from temporal constraints, a process that is proposed to rely fundamentally upon the integrity of the hippocampus. The objective of the present study was to investigate the capacity for atemporal scene construction, and its associated neural substrates, in AD. Fourteen AD patients were tested on the scene construction task and their performance was contrasted with 14 age-and education-matched healthy older Control participants. Scene construction performance was strikingly compromised in the AD group, with significant impairments evident for provision of contextual details, spatial coherence, and the overall richness of the imagined experience. Voxel-based morphometry analyses based on structural MRI revealed significant associations between scene construction capacity and atrophy in posterior parietal and lateral temporal brain structures in AD. In contrast, scene construction performance in Controls was related to integrity of frontal, parietal, and medial temporal structures, including the parahippocampal gyrus and posterior hippocampus. The posterior cingulate cortex emerged as the common region implicated for scene construction performance across participant groups. Our study highlights the importance of regions specialised for spatial and contextual processing for the construction of atemporal scenes. Damage to these regions in AD compromises the ability to construct novel scenes, leading to the recapitulation of content from previously experienced events.4

Precuneus stimulation alters the neural dynamics of autobiographical memory retrieval

“…Space-based models of memory implicate a network of regions including the hippocampus, retrosplenial cortex, and precuneus in early space-based functions believed to be central to memory retrieval (Hassabis, Kumaran, & Maguire, 2007;Irish et al, 2015;Mullally, Vargha-Khadem, & Maguire, 2014;Becker & Burgess, 2001;Byrne, Becker, & Burgess, 2007). Our 20 findings support these models, showing that the precuneus is causally involved in early memory processes, as early as 450 ms after cue presentation.…”

External details revisited – A new taxonomy for coding ‘non‐episodic’ content during autobiographical memory retrieval

“…In this regard, larger collaborative studies pooling data from across recruitment sites will be important to replicate and extend the current findings. Finally, we acknowledge that our NExt scoring system is not a direct measure of episodic or semantic memory abilities, but rather captures the tendency to provide such details within an autobiographical narrative (see also Irish et al ., ; Levine et al ., ). We contend, however, that this represents an ecologically valid insight into individuals’ ability to harness different memory types when narrating their personal past and is arguably more sensitive to fluctuations in the constituent elements of ABM across clinical syndromes and time periods.…”

Pattern similarity and connectivity of hippocampal-neocortical regions support empathy for pain

“…These findings collectively suggest a role of the hippocampus in empathy and mental simulation. Moreover, the MPFC (Benoit et al, 2010(Benoit et al, , 2014Kurczek et al, 2015;Schurz et al, 2015;Bertossi et al, 2016bBertossi et al, , 2016aBarry et al, 2019) and PCC (including precuneus and retrosplenial cortex; Vann et al, 2009;Summerfield et al, 2010;Irish et al, 2015;Schurz et al, 2015;Ramanan et al, 2018) are considered pivotal for mental construction and self-projection as well, and are also engaged during theory of mind Frith, 1999, 2006;Uddin et al, 2007;Mar, 2011). The latter additionally involves the TPJ, possibly signaling perspective taking to simulate the mental stance of another person (Saxe and Kanwisher, 2003;Saxe and Wexler, 2005;Saxe and Powell, 2006).…”