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


CONCLUSIONS
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.
Veselis
Robert A
RA
Department of Anesthesiology and Critical Care Medicine, Memorial Sloan-Kettering Cancer Center, and Weill Cornell Medical College, New York, New York 10065, USA. veselisr@mskcc.org
Pryor
Kane O
KO
Reinsel
Ruth A
RA
Li
Yuelin
Y
Mehta
Meghana
M
Johnson
Ray
R
D000293:Adolescent; D000328:Adult; D016292:Procedural Sedation / Q000523:psychology*; D003627:Data Interpretation, Statistical; D020927:Dexmedetomidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D006801:Humans; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D008297:Male; D008568:Memory / Q000187:drug effects*; D011939:Mental Recall / Q000187:drug effects; D008874:Midazolam / Q000494:pharmacology*; D008875:Middle Aged; D010775:Photic Stimulation; D015742:Propofol / Q000494:pharmacology*; D011597:Psychomotor Performance / Q000187:drug effects; D011930:Reaction Time / Q000187:drug effects; D013874:Thiopental / Q000494:pharmacology; D055815:Young Adult
D006993:Hypnotics and Sedatives; D020927:Dexmedetomidine; D013874:Thiopental; D008874:Midazolam; D015742:Propofol