Memory Priming in General Anesthesia

Memory Priming for Abstract and Concrete Words in General BIS Guided Propofol vs. Sevoflurane Anesthesia

Memory priming under general anesthesia is a phenomenon of incredible interest in the study of consciousness and unconscious cognitive processing, and for clinical practice. However results from anesthesiological literature are divergent and methodologies vary. To overcome these limits, the present study aims at better defining the phenomenon of memory priming under general anesthesia, manipulating as experimental variables both the anesthetic drug used and the stimuli primed.

Some patients may develop serious psychological sequelae after surgical intervention under general anesthesia due to implicit memory formation of intraoperative events. A number of studies in the field of anesthesiology have tried to better define the phenomenon of implicit memory in general anesthesia, with conflicting results. While some studies demonstrated the existence of unconscious memory formation also under adequate general anesthesia (BIS ranging 40-60), others state that implicit memory formation is possible only during light sedation, and that, therefore, traumatic disorders due to unconscious intraoperative memories are imputable to inadequate anesthesiological intraoperative management. The methodologies used by these studies, however, are very heterogeneous, and often inaccurate from a cognitive point of view. Data from cognitive neuroscience, in fact, demonstrate that different linguistic material, e.g. abstract and concrete words, are processed and retrieved via different networks in the brain. Then, since different anesthetics are known to target different areas of the brain, it is assumable that implicit memory formation is influenced both by the specific drug used and by the type of stimuli primed. Therefore in this experiment, the investigators aim at testing implicit memory for different word category, abstract vs. concrete words, in patients undergoing either propofol or sevoflurane general anesthesia. Also, a very strict methodology was used both for the construction of the stimuli and the stimulation and testing procedure, in order to maximize the priming effect and exclude the risk of false positive results. The investigators hypothesize that, considering the existing data on propofol and sevoflurane effects on the brain, and the known neural correlates for abstract and concrete word processing, the priming effect would be different for abstract and concrete words between patients under propofol or sevoflurane anesthesia.

Implicit memory is tested through a word stem completion test, in which the participant has to complete a three-letter stem with the first word that comes to mind. The completion test comprises both target stems (stems of word primed intra-operatively) and foils. The number of correct completions of target stems and foils is recorded as target and non target hits. The implicit score is then calculated as (target hits - nontarget hits)/total target stimuli. The score can therefore range (absolute values) from -1 to +1, where a positive score indicates memory priming.

The number of correct stem completions (hits) with nontarget words (i.e. words not heard intraoperatively)

Inclusion Criteria: patient undergoing general anesthesia for back surgery American Society of Anesthesiology (ASA) physical status classification I or II Italian native speaker right handed (assessed with the Edinburgh Handedness Inventory) not to suffer from memory deficits, hearing impairment or any other medical/psychiatric condition that could affect the memory performance or hearing Exclusion Criteria: to develop a postoperative cognitive dysfunction or delirium or any other medical complication that could prevent the memory testing or that could affect memory performance

Orena EF, Landucci F, Ayadi R, Caldiroli D, Papagno C. Propofol and sevoflurane affect intra-operative memory formation of words differently: A prospective cohort study. Eur J Anaesthesiol. 2021 Mar 1;38(Suppl 1):S50-S57. doi: 10.1097/EJA.0000000000001417.