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Morris MM, Hao 郝赵哲 ZZ, Berkowitz A. Electrophysiological Activity of Multifunctional and Behaviorally Specialized Spinal Neurons Involved in Swimming, Scratching, and Flexion Reflex in Turtles. eNeuro 2024; 11:ENEURO.0038-24.2024. [PMID: 38969499 PMCID: PMC11265262 DOI: 10.1523/eneuro.0038-24.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2024] [Revised: 06/11/2024] [Accepted: 06/26/2024] [Indexed: 07/07/2024] Open
Abstract
The adult turtle spinal cord can generate multiple kinds of limb movements, including swimming, three forms of scratching, and limb withdrawal (flexion reflex), even without brain input and sensory feedback. There are many multifunctional spinal neurons, activated during multiple motor patterns, and some behaviorally specialized neurons, activated during only one. How do multifunctional and behaviorally specialized neurons each contribute to motor output? We analyzed in vivo intracellular recordings of multifunctional and specialized neurons. Neurons tended to spike in the same phase of the hip-flexor (HF) activity cycle during swimming and scratching, though one preferred opposite phases. During both swimming and scratching, a larger fraction of multifunctional neurons than specialized neurons were highly rhythmic. One group of multifunctional neurons was active during the HF-on phase and another during the HF-off phase. Thus, HF-extensor alternation may be generated by a subset of multifunctional spinal neurons during both swimming and scratching. Scratch-specialized neurons and flexion reflex-selective neurons may instead trigger their respective motor patterns, by biasing activity of multifunctional neurons. In phase-averaged membrane potentials of multifunctional neurons, trough phases were more highly correlated between swimming and scratching than peak phases, suggesting that rhythmic inhibition plays a greater role than rhythmic excitation. We also provide the first intracellular recording of a turtle swim-specialized neuron: tonically excited during swimming but inactive during scratching and flexion reflex. It displayed an excitatory postsynaptic potential following each swim-evoking electrical stimulus and thus may be an intermediary between reticulospinal axons and the swimming CPG they activate.
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Affiliation(s)
- Madison M Morris
- School of Biological Sciences, University of Oklahoma, Norman, Oklahoma 73019
| | - Zhao-Zhe Hao 郝赵哲
- School of Biological Sciences, University of Oklahoma, Norman, Oklahoma 73019
| | - Ari Berkowitz
- School of Biological Sciences, University of Oklahoma, Norman, Oklahoma 73019
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Minassian K, Bayart A, Lackner P, Binder H, Freundl B, Hofstoetter US. Rare phenomena of central rhythm and pattern generation in a case of complete spinal cord injury. Nat Commun 2023; 14:3276. [PMID: 37280242 DOI: 10.1038/s41467-023-39034-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Accepted: 05/26/2023] [Indexed: 06/08/2023] Open
Abstract
Lumbar central pattern generators (CPGs) control the basic rhythm and coordinate muscle activation underlying hindlimb locomotion in quadrupedal mammals. The existence and function of CPGs in humans have remained controversial. Here, we investigated a case of a male individual with complete thoracic spinal cord injury who presented with a rare form of self-sustained rhythmic spinal myoclonus in the legs and rhythmic activities induced by epidural electrical stimulation (EES). Analysis of muscle activation patterns suggested that the myoclonus tapped into spinal circuits that generate muscle spasms, rather than reflecting locomotor CPG activity as previously thought. The EES-induced patterns were fundamentally different in that they included flexor-extensor and left-right alternations, hallmarks of locomotor CPGs, and showed spontaneous errors in rhythmicity. These motor deletions, with preserved cycle frequency and period when rhythmic activity resumed, were previously reported only in animal studies and suggest a separation between rhythm generation and pattern formation. Spinal myoclonus and the EES-induced activity demonstrate that the human lumbar spinal cord contains distinct mechanisms for generating rhythmic multi-muscle patterns.
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Affiliation(s)
- Karen Minassian
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Aymeric Bayart
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Peter Lackner
- Neurological Center, Clinic Penzing, Vienna, Austria
- Department of Neurology, Clinic Floridsdorf, Vienna, Austria
| | | | | | - Ursula S Hofstoetter
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
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Reale LA, Dyer MS, Perry SE, Young KM, Dickson TC, Woodhouse A, Blizzard CA. Pathologically mislocalised TDP-43 in upper motor neurons causes a die-forward spread of ALS-like pathogenic changes throughout the mouse corticomotor system. Prog Neurobiol 2023; 226:102449. [PMID: 37011806 DOI: 10.1016/j.pneurobio.2023.102449] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Revised: 02/02/2023] [Accepted: 03/24/2023] [Indexed: 04/03/2023]
Abstract
Alterations in upper motor neuron excitability are one of the earliest phenomena clinically detected in ALS, and in 97% of cases, the RNA/DNA binding protein, TDP-43, is mislocalised in upper and lower motor neurons. While these are two major pathological hallmarks in disease, our understanding of where disease pathology begins, and how it spreads through the corticomotor system, is incomplete. This project used a model where mislocalised TDP-43 was expressed in the motor cortex, to determine if localised cortical pathology could result in widespread corticomotor system degeneration. Mislocalised TDP-43 caused layer V excitatory neurons in the motor cortex to become hyperexcitable after 20 days of expression. Following cortical hyperexcitability, a spread of pathogenic changes through the corticomotor system was observed. By 30 days expression, there was a significant decrease in lower motor neuron number in the lumbar spinal cord. However, cell loss occurred selectively, with a significant loss in lumbar regions 1-3, and not lumbar regions 4-6. This regional vulnerability was associated with alterations in pre-synaptic excitatory and inhibitory proteins. Excitatory inputs (VGluT2) were increased in all lumbar regions, while inhibitory inputs (GAD65/67) were increased in lumbar regions 4-6 only. This data indicates that mislocalised TDP-43 in upper motor neurons can cause lower motor neuron degeneration. Furthermore, cortical pathology increased excitatory inputs to the spinal cord, to which local circuitry compensated with an upregulation of inhibition. These findings reveal how TDP-43 mediated pathology may spread through corticofugal tracts in ALS and identify a potential pathway for therapeutic intervention.
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Keifer J. Emergence of In Vitro Preparations and Their Contribution to Understanding the Neural Control of Behavior in Vertebrates. J Neurophysiol 2022; 128:511-526. [PMID: 35946803 DOI: 10.1152/jn.00142.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
One of the longstanding goals of the field of neuroscience is to understand the neural control of behavior in both invertebrate and vertebrate species. A series of early discoveries showed that certain motor patterns like locomotion could be generated by neuronal circuits without sensory feedback or descending control systems. These were called fictitious, or "fictive", motor programs because they could be expressed by neurons in the absence of movement. This finding lead investigators to isolate central nervous system tissue and maintain it in a dish in vitro to better study mechanisms of motor pattern generation. A period of rapid development of in vitro preparations from invertebrate species that could generate fictive motor programs from the activity of central pattern generating circuits (CPGs) emerged that was gradually followed by the introduction of such preparations from vertebrates. Here, I will review some of the notable in vitropreparations from both mammalian and non-mammalian vertebrate species developed to study the neural circuits underlying a variety of complex behaviors. This approach has been instrumental in delineating not only the cellular substrates underlying locomotion, respiration, scratching, and other behaviors, but also mechanisms underlying the modifiability of motor pathways through synaptic plasticity. In vitro preparations have had a significant impact on the field of motor systems neuroscience and the expansion of our understanding of how nervous systems control behavior. The field is ready for further advancement of this approach to explore neural substrates for variations in behavior generated by social and seasonal context, and the environment.
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Affiliation(s)
- Joyce Keifer
- Neuroscience Group, Basic Biomedical Sciences, University of South Dakota Sanford School of Medicine, Vermillion, SD, United States
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Wimalasena NK, Milner G, Silva R, Vuong C, Zhang Z, Bautista DM, Woolf CJ. Dissecting the precise nature of itch-evoked scratching. Neuron 2021; 109:3075-3087.e2. [PMID: 34411514 PMCID: PMC8497439 DOI: 10.1016/j.neuron.2021.07.020] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 06/10/2021] [Accepted: 07/26/2021] [Indexed: 01/17/2023]
Abstract
Itch is a discrete and irritating sensation tightly coupled to a drive to scratch. Acute scratching developed evolutionarily as an adaptive defense against skin irritants, pathogens, or parasites. In contrast, the itch-scratch cycle in chronic itch is harmful, inducing escalating itch and skin damage. Clinically and preclinically, scratching incidence is currently evaluated as a unidimensional motor parameter and believed to reflect itch severity. We propose that scratching, when appreciated as a complex, multidimensional motor behavior, will yield greater insight into the nature of itch and the organization of neural circuits driving repetitive motor patterns. We outline the limitations of standard measurements of scratching in rodent models and present new approaches to observe and quantify itch-evoked scratching. We argue that accurate quantitative measurements of scratching are critical for dissecting the molecular, cellular, and circuit mechanisms underlying itch and for preclinical development of therapeutic interventions for acute and chronic itch disorders.
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Affiliation(s)
- Nivanthika K Wimalasena
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA 02115, USA; Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - George Milner
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA 02115, USA
| | - Ricardo Silva
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Cliff Vuong
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Zihe Zhang
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA 02115, USA; Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Diana M Bautista
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; Hellen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720, USA.
| | - Clifford J Woolf
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA 02115, USA; Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
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Tapia JA, Reid A, Reid J, Dominguez-Nicolas SM, Manjarrez E. Modeling Post-Scratching Locomotion with Two Rhythm Generators and a Shared Pattern Formation. BIOLOGY 2021; 10:biology10070663. [PMID: 34356518 PMCID: PMC8301476 DOI: 10.3390/biology10070663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/06/2021] [Revised: 07/09/2021] [Accepted: 07/09/2021] [Indexed: 11/16/2022]
Abstract
This study aimed to present a model of post-scratching locomotion with two intermixed central pattern generator (CPG) networks, one for scratching and another for locomotion. We hypothesized that the rhythm generator layers for each CPG are different, with the condition that both CPGs share their supraspinal circuits and their motor outputs at the level of their pattern formation networks. We show that the model reproduces the post-scratching locomotion latency of 6.2 ± 3.5 s, and the mean cycle durations for scratching and post-scratching locomotion of 0.3 ± 0.09 s and 1.7 ± 0.6 s, respectively, which were observed in a previous experimental study. Our findings show how the transition of two rhythmic movements could be mediated by information exchanged between their CPG circuits through routes converging in a common pattern formation layer. This integrated organization may provide flexible and effective connectivity despite the rigidity of the anatomical connections in the spinal cord circuitry.
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Affiliation(s)
- Jesus A. Tapia
- Facultad de Ciencias Biológicas, Benemérita Universidad Autónoma de Puebla, Blvd, Valsequillo y Av. San Claudio, Ed. BIO 1, Puebla Pue 72570, Mexico;
| | - Argelia Reid
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Apartado Postal 406, Puebla Pue 72570, Mexico; (A.R.); (J.R.)
| | - John Reid
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Apartado Postal 406, Puebla Pue 72570, Mexico; (A.R.); (J.R.)
| | - Saul M. Dominguez-Nicolas
- Centro de Investigación en Micro y Nanotecnología, Universidad Veracruzana, Calzada Ruiz Cortines 455 Boca del Rio, Veracruz 94294, Mexico;
| | - Elias Manjarrez
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Apartado Postal 406, Puebla Pue 72570, Mexico; (A.R.); (J.R.)
- Correspondence: or ; Tel.: +52-22-22-95500 (ext. 7326)
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GABAergic Mechanisms Can Redress the Tilted Balance between Excitation and Inhibition in Damaged Spinal Networks. Mol Neurobiol 2021; 58:3769-3786. [PMID: 33826070 PMCID: PMC8279998 DOI: 10.1007/s12035-021-02370-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Accepted: 03/22/2021] [Indexed: 12/19/2022]
Abstract
Correct operation of neuronal networks depends on the interplay between synaptic excitation and inhibition processes leading to a dynamic state termed balanced network. In the spinal cord, balanced network activity is fundamental for the expression of locomotor patterns necessary for rhythmic activation of limb extensor and flexor muscles. After spinal cord lesion, paralysis ensues often followed by spasticity. These conditions imply that, below the damaged site, the state of balanced networks has been disrupted and that restoration might be attempted by modulating the excitability of sublesional spinal neurons. Because of the widespread expression of inhibitory GABAergic neurons in the spinal cord, their role in the early and late phases of spinal cord injury deserves full attention. Thus, an early surge in extracellular GABA might be involved in the onset of spinal shock while a relative deficit of GABAergic mechanisms may be a contributor to spasticity. We discuss the role of GABA A receptors at synaptic and extrasynaptic level to modulate network excitability and to offer a pharmacological target for symptom control. In particular, it is proposed that activation of GABA A receptors with synthetic GABA agonists may downregulate motoneuron hyperexcitability (due to enhanced persistent ionic currents) and, therefore, diminish spasticity. This approach might constitute a complementary strategy to regulate network excitability after injury so that reconstruction of damaged spinal networks with new materials or cell transplants might proceed more successfully.
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Stein PSG. Central pattern generators in the turtle spinal cord: selection among the forms of motor behaviors. J Neurophysiol 2018; 119:422-440. [PMID: 29070633 PMCID: PMC5867383 DOI: 10.1152/jn.00602.2017] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Revised: 10/16/2017] [Accepted: 10/17/2017] [Indexed: 12/29/2022] Open
Abstract
Neuronal networks in the turtle spinal cord have considerable computational complexity even in the absence of connections with supraspinal structures. These networks contain central pattern generators (CPGs) for each of several behaviors, including three forms of scratch, two forms of swim, and one form of flexion reflex. Each behavior is activated by a specific set of cutaneous or electrical stimuli. The process of selection among behaviors within the spinal cord has multisecond memories of specific motor patterns. Some spinal cord interneurons are partially shared among several CPGs, whereas other interneurons are active during only one type of behavior. Partial sharing is a proposed mechanism that contributes to the ability of the spinal cord to generate motor pattern blends with characteristics of multiple behaviors. Variations of motor patterns, termed deletions, assist in characterization of the organization of the pattern-generating components of CPGs. Single-neuron recordings during both normal and deletion motor patterns provide support for a CPG organizational structure with unit burst generators (UBGs) whose members serve a direction of a specific degree of freedom of the hindlimb, e.g., the hip-flexor UBG, the hip-extensor UBG, the knee-flexor UBG, the knee-extensor UBG, etc. The classic half-center hypothesis that includes all the hindlimb flexors in a single flexor half-center and all the hindlimb extensors in a single extensor half-center lacks the organizational complexity to account for the motor patterns produced by turtle spinal CPGs. Thus the turtle spinal cord is a valuable model system for studies of mechanisms responsible for selection and generation of motor behaviors. NEW & NOTEWORTHY The concept of the central pattern generator (CPG) is a major tenet in motor neuroethology that has influenced the design and interpretations of experiments for over a half century. This review concentrates on the turtle spinal cord and describes studies from the 1970s to the present responsible for key developments in understanding the CPG mechanisms responsible for the selection and production of coordinated motor patterns during turtle hindlimb motor behaviors.
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Affiliation(s)
- Paul S G Stein
- Department of Biology, Washington University , St. Louis, Missouri
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Hao ZZ, Berkowitz A. Shared Components of Rhythm Generation for Locomotion and Scratching Exist Prior to Motoneurons. Front Neural Circuits 2017; 11:54. [PMID: 28848402 PMCID: PMC5554521 DOI: 10.3389/fncir.2017.00054] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Accepted: 07/26/2017] [Indexed: 11/13/2022] Open
Abstract
Does the spinal cord use a single network to generate locomotor and scratching rhythms or two separate networks? Previous research showed that simultaneous swim and scratch stimulation (“dual stimulation”) in immobilized, spinal turtles evokes a single rhythm in hindlimb motor nerves with a frequency often greater than during swim stimulation alone or scratch stimulation alone. This suggests that the signals that trigger swimming and scratching converge and are integrated within the spinal cord. However, these results could not determine whether the integration occurs in motoneurons themselves or earlier, in spinal interneurons. Here, we recorded intracellularly from hindlimb motoneurons during dual stimulation. Motoneuron membrane potentials displayed regular oscillations at a higher frequency during dual stimulation than during swim or scratch stimulation alone. In contrast, arithmetic addition of the oscillations during swimming alone and scratching alone with various delays always generated irregular oscillations. Also, the standard deviation of the phase-normalized membrane potential during dual stimulation was similar to those during swimming or scratching alone. In contrast, the standard deviation was greater when pooling cycles of swimming alone and scratching alone for two of the three forms of scratching. This shows that dual stimulation generates a single rhythm prior to motoneurons. Thus, either swimming and scratching largely share a rhythm generator or the two rhythms are integrated into one rhythm by strong interactions among interneurons.
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Affiliation(s)
- Zhao-Zhe Hao
- Department of Biology, University of Oklahoma, NormanOK, United States.,Cellular and Behavioral Neurobiology Graduate Program, University of Oklahoma, NormanOK, United States
| | - Ari Berkowitz
- Department of Biology, University of Oklahoma, NormanOK, United States.,Cellular and Behavioral Neurobiology Graduate Program, University of Oklahoma, NormanOK, United States
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Trejo A, Tapia JA, De la Torre Valdovinos B, Huidobro N, Flores G, Flores-Hernandez J, Flores A, Manjarrez E. Transition of pattern generation: the phenomenon of post-scratching locomotion. Neuroscience 2014; 288:156-66. [PMID: 25556832 DOI: 10.1016/j.neuroscience.2014.12.038] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Revised: 12/17/2014] [Accepted: 12/20/2014] [Indexed: 11/29/2022]
Abstract
A fundamental problem in neurophysiology is the understanding of neuronal mechanisms by which the central nervous system produces a sequence of voluntary or involuntary motor acts from a diverse repertory of movements. These kinds of transitions between motor acts are extremely complex; however, they could be analyzed in a more simple form in decerebrate animals in the context of spinal central pattern generation. Here, we present for the first time a physiological phenomenon of post-scratching locomotion in which decerebrate cats exhibit a compulsory locomotor activity after an episode of scratching. We found flexor, extensor and intermediate single interneurons rhythmically firing in the same phase during both scratching and the subsequent post-scratching locomotion. Because no changes in phase of these neurons from scratching to post-scratching locomotion were found, we suggest that in the lumbar spinal cord there are neurons associated with both motor tasks. Moreover, because of its high reproducibility we suggest that the study of post-scratching fictive locomotion, together with the unitary recording of neurons, could become a useful tool to study neuronal mechanisms underlying transitions from one rhythmic motor task to another, and to study in more detail the central pattern generator circuitry in the spinal cord.
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Affiliation(s)
- A Trejo
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Puebla, Puebla CP 72570, Mexico
| | - J A Tapia
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Puebla, Puebla CP 72570, Mexico
| | - B De la Torre Valdovinos
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Puebla, Puebla CP 72570, Mexico
| | - N Huidobro
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Puebla, Puebla CP 72570, Mexico
| | - G Flores
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Puebla, Puebla CP 72570, Mexico
| | - J Flores-Hernandez
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Puebla, Puebla CP 72570, Mexico
| | - A Flores
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Puebla, Puebla CP 72570, Mexico
| | - E Manjarrez
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, 14 Sur 6301, Col. San Manuel, Puebla, Puebla CP 72570, Mexico.
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Premotor spinal network with balanced excitation and inhibition during motor patterns has high resilience to structural division. J Neurosci 2014; 34:2774-84. [PMID: 24553920 DOI: 10.1523/jneurosci.3349-13.2014] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Direct measurements of synaptic inhibition (I) and excitation (E) to spinal motoneurons can provide an important insight into the organization of premotor networks. Such measurements of flexor motoneurons participating in motor patterns in turtles have recently demonstrated strong concurrent E and I as well as stochastic membrane potentials and irregular spiking in the adult turtle spinal cord. These findings represent a departure from the widespread acceptance of feedforward reciprocal rate models for spinal motor function. The apparent discrepancy has been reviewed as an experimental artifact caused by the distortion of local networks in the transected turtle spinal cord. We tested this assumption in the current study by performing experiments to assess the integrity of motor functions in the intact spinal cord and the cord transected at segments D9/D10. Excitatory and inhibitory synaptic inputs to motoneurons were estimated during rhythmic motor activity and demonstrated primarily intense inputs that consisted of qualitatively similar mixed E/I before and after the transection. To understand this high functional resilience, we used mathematical modeling of networks with recurrent connectivity that could potentially explain the balanced E/I. Both experimental and modeling data support the concept of a locally balanced premotor network consisting of recurrent E/I connectivity, in addition to the well known reciprocal network activity. The multifaceted synaptic connections provide spinal networks with a remarkable ability to remain functional after structural divisions.
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12
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Giszter SF, Hart CB. Motor primitives and synergies in the spinal cord and after injury--the current state of play. Ann N Y Acad Sci 2013; 1279:114-26. [PMID: 23531009 DOI: 10.1111/nyas.12065] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Modular pattern generator elements, also known as burst synergies or motor primitives, have become a useful and important way of describing motor behavior, albeit controversial. It is suggested that these synergy elements may constitute part of the pattern-shaping layers of a McCrea/Rybak two-layer pattern generator, as well as being used in other ways in the spinal cord. The data supporting modular synergies range across species including humans and encompass motor pattern analyses and neural recordings. Recently, synergy persistence and changes following clinical trauma have been presented. These new data underscore the importance of understanding the modular structure of motor behaviors and the underlying circuitry to best provide principled therapies and to understand phenomena reported in the clinic. We discuss the evidence and different viewpoints on modularity, the neural underpinnings identified thus far, and possible critical issues for the future of this area.
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Affiliation(s)
- Simon F Giszter
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA.
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Duysens J, De Groote F, Jonkers I. The flexion synergy, mother of all synergies and father of new models of gait. Front Comput Neurosci 2013; 7:14. [PMID: 23494365 PMCID: PMC3595503 DOI: 10.3389/fncom.2013.00014] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 02/20/2013] [Indexed: 12/22/2022] Open
Abstract
Recently there has been a growing interest in the modular organization of leg movements, in particular those related to locomotion. One of the basic modules involves the flexion of the leg during swing and it was shown that this module is already present in neonates (Dominici et al., 2011). In this paper, we question how these finding build upon the original work by Sherrington, who proposed that the flexor reflex is the basic building block of flexion during swing phase. Similarly, the relation between the flexor reflex and the withdrawal reflex modules of Schouenborg and Weng (1994) will be discussed. It will be argued that there is large overlap between these notions on modules and the older concepts of reflexes. In addition, it will be shown that there is a great flexibility in the expression of some of these modules during gait, thereby allowing for a phase-dependent modulation of the appropriate responses. In particular, the end of the stance phase is a period when the flexor synergy is facilitated. It is proposed that this is linked to the activation of circuitry that is responsible for the generation of locomotor patterns (CPG, “central pattern generator”). More specifically, it is suggested that the responses in that period relate to the activation of a flexor burst generator. The latter structure forms the core of a new asymmetric model of the CPG. This activation is controlled by afferent input (facilitation by a broad range of afferents, suppression by load afferent input). Meanwhile, many of these physiologic features have found their way in the control of very flexible walking bipedal robots.
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Affiliation(s)
- Jacques Duysens
- Department of Kinesiology, KU Leuven Heverlee, Belgium ; Department of Research, Sint Maartenskliniek Nijmegen, Netherlands
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