Memory Priming in General Anesthesia

Study Overview
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Brief Summary
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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.

Detailed Description
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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.

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

Conditions
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Unconscious (Psychology)

Intervention / Treatment
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* Behavioral: Abstract priming
* Behavioral: Concrete priming
* Behavioral: Controls
* Drug: Propofol
* Drug: Sevoflurane


Participation Criteria
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Eligibility Criteria
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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

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 65 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Propofol Abstract Priming<br>Patients undergoing propofol general anesthesia and stimulation with a list of abstract words | Behavioral: Abstract priming<br>* Patients were primed with a list of abstract during their general anesthesia<br>Drug: Propofol<br>* Propofol general anesthesia<br>|
| Experimental: Propofol Concrete Priming<br>Patients undergoing propofol general anesthesia and stimulation with a list of concrete words | Behavioral: Concrete priming<br>* Patients were primed with a list of concrete during their general anesthesia<br>Drug: Propofol<br>* Propofol general anesthesia<br>|
| Active Comparator: Propofol Controls<br>Patients undergoing propofol anesthesia without any intraoperative priming | Behavioral: Controls<br>* Patients did not receive any specific stimulation with words during their general anesthesia<br>Drug: Propofol<br>* Propofol general anesthesia<br>|
| Experimental: Sevoflurane Abstract Priming<br>Patients undergoing sevoflurane general anesthesia and stimulation with a list of abstract words | Behavioral: Abstract priming<br>* Patients were primed with a list of abstract during their general anesthesia<br>Drug: Sevoflurane<br>* Sevoflurane general anesthesia<br>|
| Experimental: Sevoflurane Concrete Priming<br>Patients undergoing sevoflurane general anesthesia and stimulation with a list of concrete words | Behavioral: Concrete priming<br>* Patients were primed with a list of concrete during their general anesthesia<br>Drug: Sevoflurane<br>* Sevoflurane general anesthesia<br>|
| Active Comparator: Sevoflurane Controls<br>Patients undergoing sevoflurane general anesthesia without any intraoperative priming | Behavioral: Controls<br>* Patients did not receive any specific stimulation with words during their general anesthesia<br>Drug: Sevoflurane<br>* Sevoflurane general anesthesia<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Implicit score | 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. | 24 hours | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Explicit recall of intraoperative words | The number of intraoperative primed words that the patient is able to recall without any cue | before discharge from the Recovery Room and at 24 hours | 
| Explicit recall of intraoperative events | The explicit recall of intraoperative events assessed with the Brice Interview | before discharge from the Recovery Room and at 24 hours | 
| Target hits | The number of correct stem completions (hits) with target words (i.e. words heard intraoperatively) | 24 hours | 
| Nontarget hits | The number of correct stem completions (hits) with nontarget words (i.e. words not heard intraoperatively) | 24 hours | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Memory priming, Anesthesia, Language processing, Abstract and Concrete words, Neural correlates