Memory formation during anaesthesia: plausibility of a neurophysiological basis

Abstract

As opposed to conscious, personally relevant (explicit) memories that we can recall at will, implicit (unconscious) memories are prototypical of 'hidden' memory; memories that exist, but that we do not know we possess. Nevertheless, our behaviour can be affected by these memories; in fact, these memories allow us to function in an ever-changing world. It is still unclear from behavioural studies whether similar memories can be formed during anaesthesia. Thus, a relevant question is whether implicit memory formation is a realistic possibility during anaesthesia, considering the underlying neurophysiology. A different conceptualization of memory taxonomy is presented, the serial parallel independent model of Tulving, which focuses on dynamic information processing with interactions among different memory systems rather than static classification of different types of memories. The neurophysiological basis for subliminal information processing is considered in the context of brain function as embodied in network interactions. Function of sensory cortices and thalamic activity during anaesthesia are reviewed. The role of sensory and perisensory cortices, in particular the auditory cortex, in support of memory function is discussed. Although improbable, with the current knowledge of neurophysiology one cannot rule out the possibility of memory formation during anaesthesia.

Keywords: anaesthesia, general; hypnosis, anaesthetic; memory; memory, episodic; memory, long-term; recognition (psychology).

Fig 1

This is Tulving's conceptualization of human memory in the serial parallel independent (SPI) model. Three memory systems representing the perceptual representation system (PRS), semantic, and episodic memory are related in a hierarchical fashion during encoding, where information processing is Serial. Storage of memories is Parallel in each system, and these can be retrieved Independently. Of interest during anaesthesia is the PRS, the lowest ‘rung’ of the model (sensation). If any memory function operates during anaesthesia, it would be the PRS. It is likely that any perceptual (or sensate) memories would be stored in secondary sensory association cortices.