The Dynamics and Organization of Autobiographical Memory

Abstract

Autobiographical memory is our collection of life experiences, including those that are detailed, specific moments and those that are more general and factual. This heterogeneity translates to recruitment of a diverse neural network and allows for flexibility in retrieving the past. Memory also retains information not specific to the self and one’s personal experiences, which is often characterized as semantic memory or world knowledge. Though much has been learned from decades of research, methodological approaches from this work have overlooked important qualities of autobiographical and semantic memory. The current dissertation aimed to address two gaps in this literature by: 1) examining the temporal patterns of memory detail use during episodic autobiographical memory (EAM) elaboration, and 2) investigating the cognitive and neural bases of an understudied type of memory, namely personality trait knowledge.The first study gathered a sample of 198 healthy young, middle-aged, and older adults from seven studies of autobiographical memory for a secondary data analysis on the temporal patterns of detail use during EAM elaboration. Each transcribed memory description was segmented into five timepoints based on word count, with episodic and semantic details summed within each timepoint. Multilevel models were conducted to track the use of episodic and semantic details within EAM elaboration across the entire sample and how these temporal use patterns change with participant age and with the presence of the Apolipoprotein E ε4 allele (ApoE ε4), a risk factor for Alzheimer’s disease. The findings identified general patterns of detail use across EAM elaboration and provided support for the importance of contextual information such as semantic and scene-based details at the outset of elaboration that establish a foundation for other event details. Generally, temporal patterns were stable across participant age (with the exception of scene-based details) and between ApoE ε4 carriers and non-carriers. Lastly, semantic details initially populating an elaboration may play differential roles in EAM recollection across the adult lifespan. Study 2 examined two cases (HML040 and HML042) of severe anterograde and retrograde amnesia because of bilateral lesions to the medial temporal lobes (MTLs). They both presented with impaired ratings of their current and pre-morbid personality traits in addition to impairment in other aspects of autobiographical memory and semantic memory. Further assessment of HML040 revealed he had preserved conceptual knowledge for personality traits, could reliably and accurately rate another person’s traits, and could access his own self-concept in a variety of ways. HML042 presented with a similar cognitive profile with the exceptions that she could not reliably rate a familiar other’s personality and she had difficulty accessing her self-concept, which are likely connected to her extra-MTL lesions in the dorsal and ventro-medial prefrontal cortex (vmPFC), respectively. The results of these case studies reveal a two-component model for personality trait knowledge that hypothesizes the necessity of an effective, vmPFC driven self-concept that can draw upon an autobiographical knowledge base with spatial and/or temporal context supported by the MTLs. Collectively, these studies provide insight into the way autobiographical memories are constructed and interact with general semantic memory. These findings also help us understand why autobiographical memory is supported by such a complex, distributed neural network, and they reveal some of the fascinating ways in which our sense of self can come to mind.