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Why Does an Anesthetic Make Us Lose Consciousness?

Summary: Researchers explain anesthetics cause certain brain areas to generate less information.

Source: Goethe University Frankfurt.

Anesthetics cause certain areas of the brain to generate less information.

To date, researchers assumed that anesthetics interrupt signal transmission between different areas of the brain and that is why we lose consciousness. Neuroscientists at Goethe University Frankfurt and the Max Planck Institute for Dynamics and Self-Organization in Göttingen have now discovered that certain areas of the brain generate less information when under anesthesia. The drop in information transfer often measured when the brain is under anesthesia could be a consequence of this reduced local information generation and not – as was so far assumed – a result of disrupted signal Transmission between brain areas.

If only a few telephone calls are made in a city then it could be the case that several telecommunication systems have broken down – or it is nighttime and most people are asleep. The situation is similar in an anesthetized brain: if there is remarkably little information transfer between various areas of the brain then either signal transmission in the nerve fibers is blocked or certain areas of the brain are less active as far as the generation of information is concerned.

Image shows surgeons operating on a person.

The drop in information transfer often measured when the brain is under anesthesia could be a consequence of this reduced local information generation and not – as was so far assumed – a result of disrupted signal Transmission between brain areas. NeuroscienceNews.com image is for illustrative purposes only.

Patricia Wollstadt, Favio Frohlich, their colleagues from the Brain Imaging Center at Goethe University Frankfurt and researchers at the MPI for Dynamics and Self-Organization have now investigated this second hypothesis. As they have announced in the current issue of “PLOS Computational Biology”, they used ferrets to examine “source” brain areas from which less information was transmitted under anesthesia than in a waking state. They found out that information generation under anesthesia was far more affected there than in the “target” brain areas to which the information was transferred. This indicates that it is the information available in the source area which determines information transfer and not a disruption in signal transmission. Were the latter the case, a far greater reduction could be expected in the target areas since less information “arrives” there.

“The relevance of this alternative explanation goes beyond anesthesia research, says Patricia Wollstadt, “since each and every examination of neuronal information transfer should categorically take into consideration how much information is available locally and is therefore also transferable.”

About this neuroscience research article

Source: Michael Wibra – Goethe University Frankfurt
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Full open access research for “Breakdown of local information processing may underlie isoflurane anesthesia effects” by Patricia Wollstadt, Kristin K. Sellers, Lucas Rudelt, Viola Priesemann, Axel Hutt, Flavio Fröhlich, and Michael Wibral in PLOS Computational Biology. Published online June 1 2017 doi:10.1371/journal.pcbi.1005511

Cite This NeuroscienceNews.com Article
Goethe University Frankfurt “Why Does an Anesthetic Make Us Lose Consciousness?.” NeuroscienceNews. NeuroscienceNews, 14 June 2017.
<http://neurosciencenews.com/anesthetics-consciousness-6907/>.
Goethe University Frankfurt (2017, June 14). Why Does an Anesthetic Make Us Lose Consciousness?. NeuroscienceNew. Retrieved June 14, 2017 from http://neurosciencenews.com/anesthetics-consciousness-6907/
Goethe University Frankfurt “Why Does an Anesthetic Make Us Lose Consciousness?.” http://neurosciencenews.com/anesthetics-consciousness-6907/ (accessed June 14, 2017).

Abstract

Breakdown of local information processing may underlie isoflurane anesthesia effects

The disruption of coupling between brain areas has been suggested as the mechanism underlying loss of consciousness in anesthesia. This hypothesis has been tested previously by measuring the information transfer between brain areas, and by taking reduced information transfer as a proxy for decoupling. Yet, information transfer is a function of the amount of information available in the information source—such that transfer decreases even for unchanged coupling when less source information is available. Therefore, we reconsidered past interpretations of reduced information transfer as a sign of decoupling, and asked whether impaired local information processing leads to a loss of information transfer. An important prediction of this alternative hypothesis is that changes in locally available information (signal entropy) should be at least as pronounced as changes in information transfer. We tested this prediction by recording local field potentials in two ferrets after administration of isoflurane in concentrations of 0.0%, 0.5%, and 1.0%. We found strong decreases in the source entropy under isoflurane in area V1 and the prefrontal cortex (PFC)—as predicted by our alternative hypothesis. The decrease in source entropy was stronger in PFC compared to V1. Information transfer between V1 and PFC was reduced bidirectionally, but with a stronger decrease from PFC to V1. This links the stronger decrease in information transfer to the stronger decrease in source entropy—suggesting reduced source entropy reduces information transfer. This conclusion fits the observation that the synaptic targets of isoflurane are located in local cortical circuits rather than on the synapses formed by interareal axonal projections. Thus, changes in information transfer under isoflurane seem to be a consequence of changes in local processing more than of decoupling between brain areas. We suggest that source entropy changes must be considered whenever interpreting changes in information transfer as decoupling.

“Breakdown of local information processing may underlie isoflurane anesthesia effects” by Patricia Wollstadt, Kristin K. Sellers, Lucas Rudelt, Viola Priesemann, Axel Hutt, Flavio Fröhlich, and Michael Wibral in PLOS Computational Biology. Published online June 1 2017 doi:10.1371/journal.pcbi.1005511

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