Related Experiment Videos
Suppression of gamma activity in the human medial temporal lobe by sevoflurane anesthesia
S Uchida1, H Nakayama, T Maehara
1Department of Psychophysiology, Tokyo Institute of Psychiatry, Japan.
Abstract:
We have reported the presence of continuous gamma (30-150 Hz) activity in the human medial temporal lobe (MTL). Since the MTL is involved in learning and memory, we speculated that MTL gamma activity is related to such higher brain functions. It is thus of interest to learn how this activity changes during different states of consciousness. In this study, we recorded electrocorticographic (ECoG) activity directly from the surface of the MTL after various doses of sevoflurane anesthesia. Five epileptic patients underwent electrode placement operations in which electrodes were attached to the surfaces of the MTL and the basal temporal lobe (BTL). Immediately following the operation ECoG was recorded from each patient under four concentrations of sevoflurane anesthesia (1.5, 2.0, 2.5 and 3.0%). Fast Fourier Transform (FFT) analysis was performed on the MTL ECoGs. Under the lowest sevoflurane concentration, MTL gamma activity was observed in all patients. However, gamma activity was progressively suppressed by increased concentrations of sevoflurane, in a dose-dependent manner. Sevoflurane has been known to reduce neuronal excitability in the rat hippocampus in vitro, probably by changing GABAergic inhibition. The reduction of MTL gamma in the present study may be the result of such a mechanism. Although memory function was not tested in this study, the amount of MTL gamma activity may be related to residual memory function during anesthesia.
Insights
Continuous gamma activity in the human medial temporal lobe (MTL) decreases with higher sevoflurane anesthesia doses. This suggests a link between MTL gamma oscillations and consciousness states, potentially impacting memory function during anesthesia.
Area of Science:
- Neuroscience
- Anesthesiology
Background:
- The medial temporal lobe (MTL) is crucial for learning and memory.
- Continuous gamma (30-150 Hz) activity has been observed in the human MTL.
- Understanding how consciousness states affect MTL gamma activity is important.
Purpose of the Study:
- To investigate the effect of sevoflurane anesthesia on MTL gamma activity.
- To explore the relationship between MTL gamma activity and varying levels of consciousness.
Main Methods:
- Electrocorticography (ECoG) was recorded from the MTL and basal temporal lobe (BTL) of five epileptic patients.
- ECoG data was collected under four different concentrations of sevoflurane anesthesia (1.5%, 2.0%, 2.5%, 3.0%).
- Fast Fourier Transform (FFT) analysis was used to analyze MTL ECoG activity.
Main Results:
- MTL gamma activity was present at the lowest sevoflurane concentration.
- Increased sevoflurane concentrations progressively suppressed MTL gamma activity in a dose-dependent manner.
- The observed reduction in gamma activity may be linked to sevoflurane's known effects on GABAergic inhibition in the hippocampus.
Conclusions:
- Sevoflurane anesthesia dose-dependently suppresses continuous gamma activity in the human MTL.
- This suppression suggests a potential mechanism involving altered neuronal excitability.
- MTL gamma activity levels might correlate with residual memory function during anesthesia.