Abstract
General anesthesia is not a uniform state of the brain. Ongoing activity differs between light and deep anesthesia and cortical response properties are modulated in dependence of anesthetic dosage. We investigated how anesthesia level affects cross-modal interactions in primary sensory cortex. To examine this, we continuously measured the effects of visual and auditory stimulation during increasing and decreasing isoflurane level in the mouse visual cortex and the subiculum (from baseline at 0.7 to 2.5 vol % and reverse). Auditory evoked burst activity occurred in visual cortex after a transition during increase of anesthesia level. At the same time, auditory and visual evoked bursts occurred in the subiculum, even though the subiculum was unresponsive to both stimuli previous to the transition. This altered sensory excitability was linked to the presence of burst suppression activity in cortex, and to a regular slow burst suppression rhythm (∼0.2 Hz) in the subiculum. The effect disappeared during return to light anesthesia. The results show that pseudo-heteromodal sensory burst responses can appear in brain structures as an effect of an anesthesia induced state change.
Highlights
General anesthetics modulate cortical network properties in a dosage dependent manner
We continuously recorded the change in neuronal activity from light to deep anesthesia after increasing isoflurane concentration from 0.7% to 2.5% until long periods (.30s) of cortical suppression appeared in the local field potentials (LFPs) (Figure 1B)
Ongoing Activity In all mice, LFP activity evolved in the same typical sequence during one wash-in/wash-out cycle (Figure 1C, 2A)
Summary
General anesthetics modulate cortical network properties in a dosage dependent manner. Changes in ongoing activity during increase of anesthesia level are paralleled by changes in sensory evoked responses. Anesthetics affect ongoing neuronal activity, with an anesthesia dependent increase in correlation between cortical neurons, and a related increase in coherence of ongoing activity [5,6,7]. Increasing levels of anesthesia eventually produce burstsuppression of cortical activity, a pattern of alternating high amplitude bursts and periods of suppressed activity (silent periods) signifying deep anesthesia [8,9,10]. Does not produce a loss of brain responsiveness to sensory stimuli, but induces global changes in cortical reactivity [11,12,13,14,15,16]
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