Attenuation of High-Frequency (50–200 Hz) Thalamocortical Electroencephalographic Rhythms by Isoflurane in Rats Is More Pronounced for the Thalamus Than for the Cortex

Abstract

Isoflurane causes a concentration-dependent attenuation of the power of thalamocortical rhythms in the 30 to 200 Hz range, and this effect is more pronounced for the thalamus than for the cortex for frequencies >50 Hz. In comparison with propofol, isoflurane caused a greater attenuation in the cortex, but the effects on the thalamus were similar. Isoflurane and propofol cause common alterations of fast thalamocortical rhythms that may constitute an electrophysiologic signature of the anesthetized state.

Anesthetic Suppression of Thalamic High-Frequency Oscillations: Evidence that the Thalamus Is More Than Just a Gateway to Consciousness?

“…5 They also demonstrate that isoflurane attenuates these gamma frequency oscillations in the cortex to a greater extent than does propofol. 22 The authors used concentrations of isoflurane and propofol that were equipotent at producing loss of the righting reflex, but they note that their results may have differed if using alternative behavioral endpoints that require higher anesthetic doses (e.g., suppressing reaction to noxious stimulation).…”

“…The findings of Plourde et al 5,22 bring us one step closer in our epic quest to understand how anesthetics affect the brain. A full answer to this question 1 will require multiple levels of analysis, from an understanding of how the molecular effects of anesthetics give rise to alterations in cellular and synaptic function, which then change circuit and brain region level activity patterns to ultimately produce the cognitive and behavioral picture that we intuitively recognize as general anesthesia.…”

“…5 Specifically the authors examine how isoflurane modulates neural activity patterns in two important brain regions for information processing, the cerebral cortex and the thalamus. Because these two regions are critically important for cognition and attention, neuroscientific research has intensely focused on their association with each other.…”

“…The thalamic field potential recording data presented by Plourde and colleagues 5,22 force us to reconsider this view. Local field potential recordings mainly represent postsynaptic dendritic depolarizations rather than axonal action potentials.…”

“…For example, the steeper dose response curve for isoflurane versus propofol for cortical gamma frequency power suppression is notable, 5 and could even explain several clinical differences between these drugs. First, this finding could explain why a higher rate of awareness has been found after cases in which anesthesia is maintained with propofol (i.e.…”