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Anesthesiology. 2010 Dec;113(6):1299-309. doi: 10.1097/ALN.0b013e3181f90ccc.

Slowing of the hippocampal θ rhythm correlates with anesthetic-induced amnesia.

Author information

1
Department of Anesthesiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA. mperouansky@wisc.edu

Abstract

BACKGROUND:

Temporary, antegrade amnesia is one of the core desirable endpoints of general anesthesia. Multiple lines of evidence support a role for the hippocampal θ rhythm, a synchronized rhythmic oscillation of field potentials at 4-12 Hz, in memory formation. Previous studies have revealed a disruption of the θ rhythm at surgical levels of anesthesia. We hypothesized that θ-rhythm modulation would also occur at subhypnotic but amnestic concentrations. Therefore, we examined the effect of three inhaled agents on properties of the θ rhythm considered critical for the formation of hippocampus-dependent memories.

METHODS:

We studied the effects of halothane and nitrous oxide, two agents known to modulate different molecular targets (GABAergic [γ-aminobutyric acid] vs. non-GABAergic, respectively) and isoflurane (GABAergic and non-GABAergic targets) on fear-conditioned learning and θ oscillations in freely behaving rats.

RESULTS:

All three anesthetics slowed θ peak frequency in proportion to their inhibition of fear conditioning (by 1, 0.7, and 0.5 Hz for 0.32% isoflurane, 60% N2O, and 0.24% halothane, respectively). Anesthetics inconsistently affected other characteristics of θ oscillations.

CONCLUSIONS:

At subhypnotic amnestic concentrations, θ-oscillation frequency was the parameter most consistently affected by these three anesthetics. These results are consistent with the hypothesis that modulation of the θ rhythm contributes to anesthetic-induced amnesia.

PMID:
21042201
PMCID:
PMC3048812
DOI:
10.1097/ALN.0b013e3181f90ccc
[Indexed for MEDLINE]
Free PMC Article
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