Complexities of human memory: relevance to anaesthetic practice

Abstract

Mechanisms of anaesthetic actions on memory have largely focused on easily definable aspects of episodic memory, with emphasis on particular drug interactions on specific memory processes. However, the memory landscape of the perioperative experience includes many facets that lie outside these conceptualisations. These include patient recall of preoperative conversations, patient beliefs regarding allergies and unusual/uncommon anaesthetic events, memories of awareness, and particularly vivid dreams during anaesthesia. In no small part, memories are influenced by a patient's interpretations of events in light of their own belief systems. From the practitioner's point of view, relating fully to the patient's experience requires some framework of understanding. The purpose of this review is to highlight research over the previous decades on belief systems and their interactions with autobiographical memory, which organises episodic memories into a personally relevant narrative. As a result, memory is a set of continuously malleable processes, and is best described as a (re)constructive rather than photographic instantiation. Belief systems are separate but closely interacting processes with autobiographical memory. The interaction of a constantly evolving set of memories with belief systems can explain phenomena such as illusions, distortions, and (re)constructions of factitious events. How anaesthetics and our patient interactions influence these behaviours, and vice versa, will be important questions to explore and define with future research.

Keywords: anaesthesia; episodic; memory; mental recall.

Fig 1

This figure is an amalgam of models of human memory discussed in this paper, based on the SPI model of Tulving, which has 3 hierarchical modules. Outside experiences are processed in the perceptual representation system (PRS) and information flows to semantic and then episodic memory in a serial fashion. Information flow is represented by thick arrows, whereas comparator (black)/modulator (blue) interactions are represented by thinner arrows. Notably, episodic memory obtains knowledge of the world from semantic memories that include beliefs about the world, influenced by cultural norms. Elements of belief systems and autobiographical memories (ABMs) are incorporated in relation to Tulving's basic SPI framework where ‘episodic’ is deconstructed to emphasize interactions with belief and ABM systems. Experienced events that are novel or unexpected (star) are evaluated as to whether they are sufficiently matching previous experience and thereby accepted, or if not, then evaluated for inclusion as new memories, knowledge or beliefs. Many of these processes occur without awareness, though some may be accessible through introspection. Episodic events, potentially multiple related ones, are incorporated into constructed memories, which often comprise a mixture of veridical events and other beliefs/knowledge. Constructed memories entail processes of re-consolidation, likely enhanced during sleep. Constructed memories are incorporated into more complex ABMs to comprise a coherent sense of self. In turn, ABMs and current beliefs act as modulators of new knowledge and beliefs. Such flexibility of episodic/autobiographical memories allows planning for the future (mental time travel).