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Why Firing Rate Distributions Are Important for Understanding Spinal Central Pattern Generators

Networks in the spinal cord, which are responsible for the generation of rhythmic movements, commonly known as central pattern generators (CPGs), have remained elusive for decades. Although it is well-known that many spinal neurons are rhythmically active, little attention has been given to the dist...

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Autores principales: Lindén, Henrik, Berg, Rune W.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Frontiers Media S.A. 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8446347/
https://www.ncbi.nlm.nih.gov/pubmed/34539363
http://dx.doi.org/10.3389/fnhum.2021.719388
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author Lindén, Henrik
Berg, Rune W.
author_facet Lindén, Henrik
Berg, Rune W.
author_sort Lindén, Henrik
collection PubMed
description Networks in the spinal cord, which are responsible for the generation of rhythmic movements, commonly known as central pattern generators (CPGs), have remained elusive for decades. Although it is well-known that many spinal neurons are rhythmically active, little attention has been given to the distribution of firing rates across the population. Here, we argue that firing rate distributions can provide an important clue to the organization of the CPGs. The data that can be gleaned from the sparse literature indicate a firing rate distribution, which is skewed toward zero with a long tail, akin to a normal distribution on a log-scale, i.e., a “log-normal” distribution. Importantly, such a shape is difficult to unite with the widespread assumption of modules composed of recurrently connected excitatory neurons. Spinal modules with recurrent excitation has the propensity to quickly escalate their firing rate and reach the maximum, hence equalizing the spiking activity across the population. The population distribution of firing rates hence would consist of a narrow peak near the maximum. This is incompatible with experiments, that show wide distributions and a peak close to zero. A way to resolve this puzzle is to include recurrent inhibition internally in each CPG modules. Hence, we investigate the impact of recurrent inhibition in a model and find that the firing rate distributions are closer to the experimentally observed. We therefore propose that recurrent inhibition is a crucial element in motor circuits, and suggest that future models of motor circuits should include recurrent inhibition as a mandatory element.
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spelling pubmed-84463472021-09-18 Why Firing Rate Distributions Are Important for Understanding Spinal Central Pattern Generators Lindén, Henrik Berg, Rune W. Front Hum Neurosci Human Neuroscience Networks in the spinal cord, which are responsible for the generation of rhythmic movements, commonly known as central pattern generators (CPGs), have remained elusive for decades. Although it is well-known that many spinal neurons are rhythmically active, little attention has been given to the distribution of firing rates across the population. Here, we argue that firing rate distributions can provide an important clue to the organization of the CPGs. The data that can be gleaned from the sparse literature indicate a firing rate distribution, which is skewed toward zero with a long tail, akin to a normal distribution on a log-scale, i.e., a “log-normal” distribution. Importantly, such a shape is difficult to unite with the widespread assumption of modules composed of recurrently connected excitatory neurons. Spinal modules with recurrent excitation has the propensity to quickly escalate their firing rate and reach the maximum, hence equalizing the spiking activity across the population. The population distribution of firing rates hence would consist of a narrow peak near the maximum. This is incompatible with experiments, that show wide distributions and a peak close to zero. A way to resolve this puzzle is to include recurrent inhibition internally in each CPG modules. Hence, we investigate the impact of recurrent inhibition in a model and find that the firing rate distributions are closer to the experimentally observed. We therefore propose that recurrent inhibition is a crucial element in motor circuits, and suggest that future models of motor circuits should include recurrent inhibition as a mandatory element. Frontiers Media S.A. 2021-09-03 /pmc/articles/PMC8446347/ /pubmed/34539363 http://dx.doi.org/10.3389/fnhum.2021.719388 Text en Copyright © 2021 Lindén and Berg. https://creativecommons.org/licenses/by/4.0/This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
spellingShingle Human Neuroscience
Lindén, Henrik
Berg, Rune W.
Why Firing Rate Distributions Are Important for Understanding Spinal Central Pattern Generators
title Why Firing Rate Distributions Are Important for Understanding Spinal Central Pattern Generators
title_full Why Firing Rate Distributions Are Important for Understanding Spinal Central Pattern Generators
title_fullStr Why Firing Rate Distributions Are Important for Understanding Spinal Central Pattern Generators
title_full_unstemmed Why Firing Rate Distributions Are Important for Understanding Spinal Central Pattern Generators
title_short Why Firing Rate Distributions Are Important for Understanding Spinal Central Pattern Generators
title_sort why firing rate distributions are important for understanding spinal central pattern generators
topic Human Neuroscience
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8446347/
https://www.ncbi.nlm.nih.gov/pubmed/34539363
http://dx.doi.org/10.3389/fnhum.2021.719388
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