Autobiographical memory comprises both decontextualized personal semantics and contextualized episodic memories. It allows for the development and maintenance of our unique personal identity and self-awareness, namely autonoetic consciousness. More specifically, episodic autobiographical memory refers to the ability to recollect and re-experience events of our own life occurring at a particular time and place. Memory deficit is the hallmark for early diagnosis of Alzheimer's Disease (AD) and it is strictly linked to tau- and amyloid-related hippocampal atrophy; however, memory deficit in AD may have its root in subtle alteration of spatial and temporal processing in prodromal stage of AD, such as Subjective Cognitive Decline (SCD). Indeed, representation of space and time may be altered before the clinical onset of the memory impairment. These reports are consistent with early atrophy of brain structures of context association and memory, namely parahippocampal, perirhinal and entorhinal cortices and subtle disconnection between the crucial nodes of autobiographical memory detected in prodromal stages of AD.
Thus, space and time are two key components of autobiographical episodic memories; NAM will disentangle whether they subtend misrepresentation of autobiographical episodic memories in SCD. Due to its impact on memory process, we will also take into account the role of cognitive failures ingenerated by chronic or acute stress states.
From a theoretical perspective, NAM will provide new evidence for a novel integrated neuroscientific account of autobiographical memory, disclosing the way in which our brain processes and organizes previous experiences. New important insights will be derived for clinical applications, as well. First, NAM will open new areas of investigations in neuropsychological rehabilitation of memory deficits, with substantial impact on society. Also, it will disentangle the role of chronic and acute stress states on memory deficits in aging
Even if recent review of literature points toward the idea that the hippocampus (HC) is pivotal in processing spatial and temporal relations between stimuli and that it provides the neural basis of cognitive mapping by means of a sort of chunking of experiences with low spatial and temporal variance [1], direct evidence in humans is lacking. Also, even if the hippocampal contribution to memory formation is currently undoubted, its contribution to remote memories is still a matter of debate [2].
Here we expected that SCD will differ from HC on measures of episodic autobiographical memories, not semantic one. In SCD, we expect also that spatial and temporal processing predict the number of episodic details (i.e. internal scores: event, place, time, perceptual and emotion/thought) collected using AI. Episodic autobiographical memories, provided using AFT, should be predicted by performances on spatial and temporal tasks as well. Considering the importance of stress-related effects on memory and hippocampal volume [3], we also expect that autobiographical memories will be partially associated with stress-related CF in both SCD and HC.
NAM's results will provide useful theoretical and clinical insights. On the one hand if successful, NAM will provide compelling evidence into the way in which our brain processes and organizes knowledge about who we are, namely autobiographical memory, and its pitfalls. On the other hand, it will have important applications for a widespread condition, namely AD. The increase of life-expectancy will inevitably entail the progressive increase of pathological ageing: the number of patients with dementia is going to nearly double every 20 years, reaching the 115 million by 2050 (World Alzheimer Report 2015). Deficit in episodic autobiographical memory is widely reported in AD patients and it is dramatically associated with degradation of patients' self-knowledge and sense of identity. NAM, disclosing the way in which our brain processes and organizes previous experience, will open new areas of investigations in neuropsychological rehabilitation of memory deficits - especially in preclinical and early stages of AD - with substantial impact on society. This possibility is further sustained by a recent paper by our group in which we found that training spatial abilities yielded to improved memory performances [4] and the phylogenetic hypothesis by Buzsaki and Moser [5], according to which mechanisms of memory have evolved from mechanisms initially introduced to navigate within real environmental space, such as hippocampal place fields. Finally, our study may offer preliminary insights on the possibility to consider measures of cognitive failures as a signal of potential clinical impairments; stress-related effects on autobiographical memory will be disentangled, as well.
1. Ekstrom et al. Hippocampus 28, 680-687 (2017)
2. Boccia et al. NBB 107, 84-95 (2019)
3. Karl et al. Neu Biobeh Rev 30, 1004-1031 (2006)
3. Boccia et al. Front Hum Neurosci 13, 322 (2019)
4. Buzsaki et al. Nat Neurosci 16, 130-138 (2013)