scholarly journals Altered stimulus representation in rat auditory cortex is not causal for loss of consciousness under general anaesthesia

2018 ◽  
Vol 121 (3) ◽  
pp. 605-615 ◽  
Author(s):  
M.I. Banks ◽  
N.S. Moran ◽  
B.M. Krause ◽  
S.M. Grady ◽  
D.J. Uhlrich ◽  
...  
2017 ◽  
Author(s):  
Matthew I. Banks ◽  
Bryan M. Krause ◽  
Nicholas S. Moran ◽  
Sean M. Grady ◽  
Jeremiah Kakes ◽  
...  

AbstractThe mechanism whereby anesthetics cause loss of consciousness (LOC) is poorly understood. Current theories suggest that impaired representation of information in cortico-thalamic networks contributes to LOC under anesthesia. We sought to determine whether such changes are present in auditory cortex using information theoretic analysis of multiunit responses in rats. We tested the effects of three agents with different molecular targets: isoflurane, which acts at multiple pre- and postsynaptic loci, propofol, which acts primarily on GABAA receptors, and dexmedetomidine, an α2 adrenergic agonist. We reasoned that changes in the representation of sensory stimuli causative for LOC would be present regardless of the molecular target of the anesthetic. All three agents caused LOC, as assayed by the loss of righting reflex (LORR). We presented acoustic stimuli that varied across a wide range of temporal and spectral dynamics under control, sub-hypnotic (i.e. dose too low to cause LORR), just-hypnotic (a dose just sufficient to cause LORR) and recovery conditions. Changes in mutual information (MI) between the stimulus and spike responses under anesthesia diverged in two ways from predictions of a model in which stimulus representation is impaired upon LOC. First, the sign of changes in MI was agent-specific: MI increased under dexmedetomidine, while it decreased under isoflurane and propofol. Second, there was no consistent change in MI when transitioning from sub-hyptnotic to just-hypnotic doses: for none of the agents did MI decrease at the higher dose, and in some cases MI actually increased relative to the sub-hypnotic dose. Changes in MI under anesthesia were strongly correlated with changes in precision and reliability of spike timing, consistent with the importance of temporal stimulus features in driving auditory cortical activity. These data indicate that primary sensory cortex is not the locus for changes in information representation causative for LOC under anesthesia.


2021 ◽  
pp. 31-34
Author(s):  
Chetan Srinath ◽  
Alan Yates

The evolution of surgical anaesthesia began nearly 175 years ago with the first public demonstration in 1846 by William G. Morton. Modern anaesthetic techniques have developed in keeping with our understanding of human physiology and the demands of surgical innovation. Anaesthesia can be local, regional, or general and plastic surgery lends itself to local or regional techniques. Local anaesthesia infiltrates the active agent throughout the area in question, while regional anaesthesia uses discrete placement of the anaesthetic agent to block the conduction in nerves supplying sensibility to a wide predictable area. General anaesthesia involves complete loss of consciousness and awareness.


2014 ◽  
Vol 19 (5) ◽  
pp. 3-12
Author(s):  
Lorne Direnfeld ◽  
David B. Torrey ◽  
Jim Black ◽  
LuAnn Haley ◽  
Christopher R. Brigham

Abstract When an individual falls due to a nonwork-related episode of dizziness, hits their head and sustains injury, do workers’ compensation laws consider such injuries to be compensable? Bearing in mind that each state makes its own laws, the answer depends on what caused the loss of consciousness, and the second asks specifically what happened in the fall that caused the injury? The first question speaks to medical causation, which applies scientific analysis to determine the cause of the problem. The second question addresses legal causation: Under what factual circumstances are injuries of this type potentially covered under the law? Much nuance attends this analysis. The authors discuss idiopathic falls, which in this context means “unique to the individual” as opposed to “of unknown cause,” which is the familiar medical terminology. The article presents three detailed case studies that describe falls that had their genesis in episodes of loss of consciousness, followed by analyses by lawyer or judge authors who address the issue of compensability, including three scenarios from Arizona, California, and Pennsylvania. A medical (scientific) analysis must be thorough and must determine the facts regarding the fall and what occurred: Was the fall due to a fit (eg, a seizure with loss of consciousness attributable to anormal brain electrical activity) or a faint (eg, loss of consciousness attributable to a decrease in blood flow to the brain? The evaluator should be able to fully explain the basis for the conclusions, including references to current science.


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