Drug-induced Amnesia Is a Separate Phenomenon from Sedation Electrophysiologic Evidence

  • Veselis R
  • Reinsel R
  • Feshchenko V
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Background: Sedative– hypnotic drugs not only increase se-dation, but also impair memory as serum concentration in-creases. These drugs also produce profound changes in the auditory event-related potential (ERP). The ability of various ERP components to predict changes in sedation and memory produced by various drugs was tested. Methods: Sixty-five healthy volunteers randomly received in-travenous placebo, midazolam, propofol, thiopental, fentanyl with ondansetron, or ondansetron alone at five different stable target concentrations (three increasing, two decreasing) using a computer-controlled infusion pump to produce varying de-grees of sedation without loss of consciousness. ERPs were recorded while volunteer participants detected a deviant audi-tory stimulus and made a button-press response to a target tone (standard oddball paradigm, 80:20 ratio, to elicit a P3 response). At each target concentration, volunteers learned a list of 16 words. The predictive probabilities (P k) of various ERP compo-nents were determined for word recognition at the end of the day (memory) and log reaction time to the deviant stimulus (sedation). Results: The N2 latency of the ERP consistently predicted log reaction time in all groups (P k ؎ SE from 0.58 ؎ 0.04 to 0.71 ؎ 0.04). The N2P3 amplitude of the ERP was the best predictor of memory performance for midazolam (P k , 0.63 ؎ 0.04), propofol (P k , 0.62 ؎ 0.05), and thiopental (P k , 0.66 ؎ 0.04). There was a differential ability to predict memory performance from seda-tion for midazolam and propofol. Conclusions: Midazolam and propofol affect memory differ-entially from their sedative effects, and these are indexed by specific components of the auditory ERP. These components of the ERP are associated with specific, but not necessarily unique, neuroanatomic structures. Thus, these drugs act by additional mechanisms beyond general central nervous system depres-sion to produce the effects of sedation and memory impairment. THE sedative and amnesic effects of sedative– hypnotic drugs are closely related, as sedation itself produces impairment in memory performance, and both effects vary in the same direction as serum concentration chang-es. 1,2 There is evidence that separate neuroanatomic regions mediate arousal or attention versus memory pro-cesses in humans who have not received any drug,

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  • Robert A Veselis

  • Ruth A Reinsel

  • Vladimir A Feshchenko

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