Low-dose propofol-induced amnesia is not due to a failure of encoding: left inferior prefrontal cortex is still active.
BACKGROUND
Propofol may produce amnesia by affecting encoding. The hypothesis that propofol weakens encoding was tested by measuring regional cerebral blood flow during verbal encoding.


METHODS
Seventeen volunteer participants (12 men; aged 30.4 +/- 6.5 yr) had regional cerebral blood flow measured using H2O positron emission tomography during complex and simple encoding tasks (deep vs. shallow level of processing) to identify a region of interest in the left inferior prefrontal cortex (LIPFC). The effect of either propofol (n = 6, 0.9 microg/ml target concentration), placebo with a divided attention task (n = 5), or thiopental at sedative doses (n = 6, 3 microg/ml) on regional cerebral blood flow activation in the LIPFC was tested. The divided attention task was expected to decrease activation in the LIPFC.


RESULTS
Propofol did not impair encoding performance or reaction times, but impaired recognition memory of deeply encoded words 4 h later (median recognition of 35% [interquartile range, 17-54%] of words presented during propofol vs. 65% [38-91%] before drug; P < 0.05). Statistical parametric mapping analysis identified a region of interest of 6.6 cm in the LIPFC (T = 7.44, P = 0.014). Regional cerebral blood flow response to deep encoding was present in this region of interest in each group before drug (T > 4.41, P < 0.04). During drug infusion, only the propofol group continued to have borderline significant activation in this region (T = 4.00, P = 0.063).


CONCLUSIONS
If the amnesic effect of propofol were solely due to effects on encoding, activation in the LIPFC should be minimal. Because LIPFC activation was not totally eliminated by propofol, the amnesic action of propofol must be present in other brain regions and/or affect other memory processes.
Veselis
Robert A
RA
Department of Anesthesiology (Box 24), Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA. veselisr@mskcc.org
Pryor
Kane O
KO
Reinsel
Ruth A
RA
Mehta
Meghana
M
Pan
Hong
H
Johnson
Ray
R
D000328:Adult; D000647:Amnesia / Q000139:chemically induced*; D054022:Cerebrum / Q000098:blood supply*; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects; D005260:Female; D006801:Humans; D006993:Hypnotics and Sedatives / Q000009:adverse effects* / Q000494:pharmacology; D008297:Male; D049268:Positron-Emission Tomography; D017397:Prefrontal Cortex / Q000187:drug effects*; D015742:Propofol / Q000009:adverse effects* / Q000494:pharmacology; D011597:Psychomotor Performance / Q000187:drug effects*; D013874:Thiopental / Q000009:adverse effects / Q000494:pharmacology
D006993:Hypnotics and Sedatives; D013874:Thiopental; D015742:Propofol