Propofol and midazolam inhibit conscious memory processes very soon after encoding: an event-related potential study of familiarity and recollection in volunteers

Anesthesiology. 2009 Feb;110(2):295-312. doi: 10.1097/ALN.0b013e3181942ef0.


Background: Intravenous drugs active via gamma-aminobutyric acid receptors to produce memory impairment during conscious sedation. Memory function was assessed using event-related potentials (ERPs) while drug was present.

Methods: The continuous recognition task measured recognition of photographs from working (6 s) and long-term (27 s) memory while ERPs were recorded from Cz (familiarity recognition) and Pz electrodes (recollection recognition). Volunteer participants received sequential doses of one of placebo (n = 11), 0.45 and 0.9 microg/ml propofol (n = 10), 20 and 40 ng/ml midazolam (n = 12), 1.5 and 3 microg/ml thiopental (n = 11), or 0.25 and 0.4 ng/ml dexmedetomidine (n = 11). End-of-day yes/no recognition 225 min after the end of drug infusion tested memory retention of pictures encoded on the continuous recognition tasks.

Results: Active drugs increased reaction times and impaired memory on the continuous recognition task equally, except for a greater effect of midazolam (P < 0.04). Forgetting from continuous recognition tasks to end of day was similar for all drugs (P = 0.40), greater than placebo (P < 0.001). Propofol and midazolam decreased the area between first presentation (new) and recognized (old, 27 s later) ERP waveforms from long-term memory for familiarity (P = 0.03) and possibly for recollection processes (P = 0.12). Propofol shifted ERP amplitudes to smaller voltages (P < 0.002). Dexmedetomidine may have impaired familiarity more than recollection processes (P = 0.10). Thiopental had no effect on ERPs.

Conclusion: Propofol and midazolam impaired recognition ERPs from long-term memory but not working memory. ERP measures of memory revealed different pathways to end-of-day memory loss as early as 27 s after encoding.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Conscious Sedation / psychology*
  • Data Interpretation, Statistical
  • Dexmedetomidine / pharmacology
  • Dose-Response Relationship, Drug
  • Electroencephalography / drug effects
  • Evoked Potentials / drug effects
  • Female
  • Humans
  • Hypnotics and Sedatives / pharmacology*
  • Male
  • Memory / drug effects*
  • Mental Recall / drug effects
  • Midazolam / pharmacology*
  • Middle Aged
  • Photic Stimulation
  • Propofol / pharmacology*
  • Psychomotor Performance / drug effects
  • Reaction Time / drug effects
  • Thiopental / pharmacology
  • Young Adult


  • Hypnotics and Sedatives
  • Dexmedetomidine
  • Thiopental
  • Midazolam
  • Propofol