Low-dose Propofol-induced Amnesia Is Not due to a Failure of Encoding : Left Inferior Prefrontal Cortex Is Still Active

• Published in: Anesthesiology (Philadelphia) 2008-08, Vol.109 (2), p.213-224
• Main Authors: VESELIS, Robert A, PRYOR, Kane O, REINSEL, Ruth A, MEHTA, Meghana, HONG PAN, JOHNSON, Ray
• Format: Article
• Language: English
• Subjects: Adult; Amnesia - chemically induced; Anesthesia; Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Biological and medical sciences; Cerebrum - blood supply; Dose-Response Relationship, Drug; Electroencephalography - drug effects; Female; Humans; Hypnotics and Sedatives - adverse effects; Hypnotics and Sedatives - pharmacology; Male; Medical sciences; Positron-Emission Tomography; Prefrontal Cortex - drug effects; Propofol - adverse effects; Propofol - pharmacology; Psychomotor Performance - drug effects; Thiopental - adverse effects; Thiopental - pharmacology
• ISSN: 0003-3022; 1528-1175
• DOI: 10.1097/ALN.0b013e31817fd8ae

Propofol may produce amnesia by affecting encoding. The hypothesis that propofol weakens encoding was tested by measuring regional cerebral blood flow during verbal encoding. 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. 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). 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.