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From decision to action: Detailed modelling of frog tadpoles reveals neuronal mechanisms of decision-making and reproduces unpredictable swimming movements in response to sensory signals. PLoS Comput Biol 2021; 17:e1009654. [PMID: 34898604 PMCID: PMC8699619 DOI: 10.1371/journal.pcbi.1009654] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 12/23/2021] [Accepted: 11/17/2021] [Indexed: 01/30/2023] Open
Abstract
How does the brain process sensory stimuli, and decide whether to initiate locomotor behaviour? To investigate this question we develop two whole body computer models of a tadpole. The "Central Nervous System" (CNS) model uses evidence from whole-cell recording to define 2300 neurons in 12 classes to study how sensory signals from the skin initiate and stop swimming. In response to skin stimulation, it generates realistic sensory pathway spiking and shows how hindbrain sensory memory populations on each side can compete to initiate reticulospinal neuron firing and start swimming. The 3-D "Virtual Tadpole" (VT) biomechanical model with realistic muscle innervation, body flexion, body-water interaction, and movement is then used to evaluate if motor nerve outputs from the CNS model can produce swimming-like movements in a volume of "water". We find that the whole tadpole VT model generates reliable and realistic swimming. Combining these two models opens new perspectives for experiments.
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Roussel Y, Gaudreau SF, Kacer ER, Sengupta M, Bui TV. Modeling spinal locomotor circuits for movements in developing zebrafish. eLife 2021; 10:e67453. [PMID: 34473059 PMCID: PMC8492062 DOI: 10.7554/elife.67453] [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: 02/11/2021] [Accepted: 09/01/2021] [Indexed: 01/16/2023] Open
Abstract
Many spinal circuits dedicated to locomotor control have been identified in the developing zebrafish. How these circuits operate together to generate the various swimming movements during development remains to be clarified. In this study, we iteratively built models of developing zebrafish spinal circuits coupled to simplified musculoskeletal models that reproduce coiling and swimming movements. The neurons of the models were based upon morphologically or genetically identified populations in the developing zebrafish spinal cord. We simulated intact spinal circuits as well as circuits with silenced neurons or altered synaptic transmission to better understand the role of specific spinal neurons. Analysis of firing patterns and phase relationships helped to identify possible mechanisms underlying the locomotor movements of developing zebrafish. Notably, our simulations demonstrated how the site and the operation of rhythm generation could transition between coiling and swimming. The simulations also underlined the importance of contralateral excitation to multiple tail beats. They allowed us to estimate the sensitivity of spinal locomotor networks to motor command amplitude, synaptic weights, length of ascending and descending axons, and firing behavior. These models will serve as valuable tools to test and further understand the operation of spinal circuits for locomotion.
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Affiliation(s)
- Yann Roussel
- Brain and Mind Research Institute, Centre for Neural Dynamics, Department of Biology, University of OttawaOttawaCanada
- Blue Brain Project, École Polytechnique Fédérale de LausanneGenèveSwitzerland
| | - Stephanie F Gaudreau
- Brain and Mind Research Institute, Centre for Neural Dynamics, Department of Biology, University of OttawaOttawaCanada
| | - Emily R Kacer
- Brain and Mind Research Institute, Centre for Neural Dynamics, Department of Biology, University of OttawaOttawaCanada
| | - Mohini Sengupta
- Washington University School of Medicine, Department of NeuroscienceSt LouisUnited States
| | - Tuan V Bui
- Brain and Mind Research Institute, Centre for Neural Dynamics, Department of Biology, University of OttawaOttawaCanada
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Roberts A, Borisyuk R, Buhl E, Ferrario A, Koutsikou S, Li WC, Soffe SR. The decision to move: response times, neuronal circuits and sensory memory in a simple vertebrate. Proc Biol Sci 2020; 286:20190297. [PMID: 30900536 DOI: 10.1098/rspb.2019.0297] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
All animals use sensory systems to monitor external events and have to decide whether to move. Response times are long and variable compared to reflexes, and fast escape movements. The complexity of adult vertebrate brains makes it difficult to trace the neuronal circuits underlying basic decisions to move. To simplify the problem, we investigate the nervous system and responses of hatchling frog tadpoles which swim when their skin is stimulated. Studying the neuron-by-neuron pathway from sensory to hindbrain neurons, where the decision to swim is made, has revealed two simple pathways generating excitation which sums to threshold in these neurons to initiate swimming. The direct pathway leads to short, and reliable delays like an escape response. The other includes a population of sensory processing neurons which extend firing to introduce noise and delay into responses. These neurons provide a brief, sensory memory of the stimulus, that allows tadpoles to integrate stimuli occurring within a second or so of each other. We relate these findings to other studies and conclude that sensory memory makes a fundamental contribution to simple decisions and is present in the brainstem of a basic vertebrate at a surprisingly early stage in development.
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Affiliation(s)
- Alan Roberts
- 1 School of Biological Sciences, University of Bristol , Bristol BS8 1TQ , UK
| | - Roman Borisyuk
- 2 School of Computing, Electronics and Mathematics, University of Plymouth , Plymouth PL4 8AA , UK
| | - Edgar Buhl
- 1 School of Biological Sciences, University of Bristol , Bristol BS8 1TQ , UK.,3 School of Physiology, Pharmacology and Neuroscience, University of Bristol , Bristol BS8 1TD , UK
| | - Andrea Ferrario
- 2 School of Computing, Electronics and Mathematics, University of Plymouth , Plymouth PL4 8AA , UK
| | - Stella Koutsikou
- 1 School of Biological Sciences, University of Bristol , Bristol BS8 1TQ , UK.,4 Medway School of Pharmacy, University of Kent , Chatham Maritime ME4 4TB , UK
| | - Wen-Chang Li
- 5 School of Psychology and Neuroscience, University of St Andrews , St Andrews KY16 9JP , UK
| | - Stephen R Soffe
- 1 School of Biological Sciences, University of Bristol , Bristol BS8 1TQ , UK
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Berkowitz A. Expanding our horizons: central pattern generation in the context of complex activity sequences. J Exp Biol 2019; 222:222/20/jeb192054. [DOI: 10.1242/jeb.192054] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
ABSTRACT
Central pattern generators (CPGs) are central nervous system (CNS) networks that can generate coordinated output in the absence of patterned sensory input. For decades, this concept was applied almost exclusively to simple, innate, rhythmic movements with essentially identical cycles that repeat continually (e.g. respiration) or episodically (e.g. locomotion). But many natural movement sequences are not simple rhythms, as they include different elements in a complex order, and some involve learning. The concepts and experimental approaches of CPG research have also been applied to the neural control of complex movement sequences, such as birdsong, though this is not widely appreciated. Experimental approaches to the investigation of CPG networks, both for simple rhythms and for complex activity sequences, have shown that: (1) brief activation of the CPG elicits a long-lasting naturalistic activity sequence; (2) electrical stimulation of CPG elements alters the timing of subsequent cycles or sequence elements; and (3) warming or cooling CPG elements respectively speeds up or slows down the rhythm or sequence rate. The CPG concept has also been applied to the activity rhythms of populations of mammalian cortical neurons. CPG concepts and methods might further be applied to a variety of fixed action patterns typically used in courtship, rivalry, nest building and prey capture. These complex movements could be generated by CPGs within CPGs (‘nested’ CPGs). Stereotypical, non-motor, non-rhythmic neuronal activity sequences may also be generated by CPGs. My goal here is to highlight previous applications of the CPG concept to complex but stereotypical activity sequences and to suggest additional possible applications, which might provoke new hypotheses and experiments.
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Affiliation(s)
- Ari Berkowitz
- Department of Biology and Cellular & Behavioral Neurobiology Graduate Program, University of Oklahoma, Norman, OK 73019, USA
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Koutsikou S, Merrison‐Hort R, Buhl E, Ferrario A, Li W, Borisyuk R, Soffe SR, Roberts A. A simple decision to move in response to touch reveals basic sensory memory and mechanisms for variable response times. J Physiol 2018; 596:6219-6233. [PMID: 30074236 PMCID: PMC6292811 DOI: 10.1113/jp276356] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 07/13/2018] [Indexed: 01/28/2023] Open
Abstract
KEY POINTS Short-term working memory and decision-making are usually studied in the cerebral cortex; in many models of simple decision making, sensory signals build slowly and noisily to threshold to initiate a motor response after long, variable delays. When touched, hatchling frog tadpoles decide whether to swim; we define the long and variable delays to swimming and use whole-cell recordings to uncover the neurons and processes responsible. Firing in sensory and sensory pathway neurons is short latency, and too brief and invariant to explain these delays, while recordings from hindbrain reticulospinal neurons controlling swimming reveal a prolonged and variable build-up of synaptic excitation which can reach firing threshold and initiate swimming. We propose this excitation provides a sensory memory of the stimulus and may be generated by small reverberatory hindbrain networks. Our results uncover fundamental network mechanisms that allow animals to remember brief sensory stimuli and delay simple motor decisions. ABSTRACT Many motor responses to sensory input, like locomotion or eye movements, are much slower than reflexes. Can simpler animals provide fundamental answers about the cellular mechanisms for motor decisions? Can we observe the 'accumulation' of excitation to threshold proposed to underlie decision making elsewhere? We explore how somatosensory touch stimulation leads to the decision to swim in hatchling Xenopus tadpoles. Delays measured to swimming in behaving and immobilised tadpoles are long and variable. Activity in their extensively studied sensory and sensory pathway neurons is too short-lived to explain these response delays. Instead, whole-cell recordings from the hindbrain reticulospinal neurons that drive swimming show that these receive prolonged, variable synaptic excitation lasting for nearly a second following a brief stimulus. They fire and initiate swimming when this excitation reaches threshold. Analysis of the summation of excitation requires us to propose extended firing in currently undefined presynaptic hindbrain neurons. Simple models show that a small excitatory recurrent-network inserted in the sensory pathway can mimic this process. We suggest that such a network may generate slow, variable summation of excitation to threshold. This excitation provides a simple memory of the sensory stimulus. It allows temporal and spatial integration of sensory inputs and explains the long, variable delays to swimming. The process resembles the 'accumulation' of excitation proposed for cortical circuits in mammals. We conclude that fundamental elements of sensory memory and decision making are present in the brainstem at a surprisingly early stage in development.
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Affiliation(s)
- Stella Koutsikou
- School of Biological SciencesUniversity of Bristol24 Tyndall AvenueBristolBS8 1TQUK
- Medway School of PharmacyUniversity of KentAnson Building, Central AvenueChatham MaritimeME4 4 TBUK
| | - Robert Merrison‐Hort
- School of ComputingElectronics and MathematicsUniversity of PlymouthDrake CircusPlymouthPL4 8AAUK
| | - Edgar Buhl
- School of Biological SciencesUniversity of Bristol24 Tyndall AvenueBristolBS8 1TQUK
| | - Andrea Ferrario
- School of ComputingElectronics and MathematicsUniversity of PlymouthDrake CircusPlymouthPL4 8AAUK
| | - Wen‐Chang Li
- School of Psychology and NeuroscienceUniversity of St Andrews9 South StreetSt AndrewsFifeKY16 9JPUK
| | - Roman Borisyuk
- School of ComputingElectronics and MathematicsUniversity of PlymouthDrake CircusPlymouthPL4 8AAUK
| | - Stephen R. Soffe
- School of Biological SciencesUniversity of Bristol24 Tyndall AvenueBristolBS8 1TQUK
| | - Alan Roberts
- School of Biological SciencesUniversity of Bristol24 Tyndall AvenueBristolBS8 1TQUK
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Picton LD, Sillar KT, Zhang HY. Control of Xenopus Tadpole Locomotion via Selective Expression of Ih in Excitatory Interneurons. Curr Biol 2018; 28:3911-3923.e2. [PMID: 30503615 PMCID: PMC6303192 DOI: 10.1016/j.cub.2018.10.048] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Revised: 09/06/2018] [Accepted: 10/22/2018] [Indexed: 11/16/2022]
Abstract
Locomotion relies on the coordinated activity of rhythmic neurons in the hindbrain and spinal cord and depends critically on the intrinsic properties of excitatory interneurons. Therefore, understanding how ion channels sculpt the properties of these interneurons, and the consequences for circuit function and behavior, is an important task. The hyperpolarization-activated cation current, Ih, is known to play important roles in shaping neuronal properties and for rhythm generation in many neuronal networks. We show in stage 42 Xenopus laevis frog tadpoles that Ih is strongly expressed only in excitatory descending interneurons (dINs), an important ipsilaterally projecting population that drives swimming activity. The voltage-dependent HCN channel blocker ZD7288 completely abolished a prominent depolarizing sag potential in response to hyperpolarization, the hallmark of Ih, and hyperpolarized dINs. ZD7288 also affected dIN post-inhibitory rebound firing, upon which locomotor rhythm generation relies, and disrupted locomotor output. Block of Ih also unmasked an activity-dependent ultraslow afterhyperpolarization (usAHP) in dINs following swimming, mediated by a dynamic Na/K pump current. This usAHP, unmasked in dINs by ZD7288, resulted in suprathreshold stimuli failing to evoke swimming at short inter-swim intervals, indicating an important role for Ih in maintaining swim generation capacity and in setting the post-swim refractory period of the network. Collectively, our data suggest that the selective expression of Ih in dINs determines specific dIN properties that are important for rhythm generation and counteracts an activity-dependent usAHP to ensure that dINs can maintain coordinated swimming over a wide range of inter-swim intervals. Ih is strongly expressed in Xenopus locomotor-rhythm-generating dIN interneurons Ih is active at rest in dINs, contributing to their distinct electrical properties dINs normally lack a Na pump-dependent ultra-slow afterhyperpolarization (usAHP) Ih counterbalances dIN usAHPs to preserve tadpole rhythm generating capacity
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Affiliation(s)
- Laurence D Picton
- School of Psychology and Neuroscience, University of St Andrews, St Andrews KY16 9JP, UK
| | - Keith T Sillar
- School of Psychology and Neuroscience, University of St Andrews, St Andrews KY16 9JP, UK
| | - Hong-Yan Zhang
- Centre for Discovery Brain Sciences, Edinburgh Medical School, University of Edinburgh, Edinburgh EH16 4SB, UK.
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Ferrario A, Merrison-Hort R, Soffe SR, Borisyuk R. Structural and functional properties of a probabilistic model of neuronal connectivity in a simple locomotor network. eLife 2018; 7:33281. [PMID: 29589828 PMCID: PMC5910024 DOI: 10.7554/elife.33281] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Accepted: 03/25/2018] [Indexed: 11/13/2022] Open
Abstract
Although, in most animals, brain connectivity varies between individuals, behaviour is often similar across a species. What fundamental structural properties are shared across individual networks that define this behaviour? We describe a probabilistic model of connectivity in the hatchling Xenopus tadpole spinal cord which, when combined with a spiking model, reliably produces rhythmic activity corresponding to swimming. The probabilistic model allows calculation of structural characteristics that reflect common network properties, independent of individual network realisations. We use the structural characteristics to study examples of neuronal dynamics, in the complete network and various sub-networks, and this allows us to explain the basis for key experimental findings, and make predictions for experiments. We also study how structural and functional features differ between detailed anatomical connectomes and those generated by our new, simpler, model (meta-model).
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Affiliation(s)
- Andrea Ferrario
- School of Computing, Electronics and Mathematics, University of Plymouth, Plymouth, United Kingdom
| | - Robert Merrison-Hort
- School of Computing, Electronics and Mathematics, University of Plymouth, Plymouth, United Kingdom
| | - Stephen R Soffe
- School of Biological Sciences, University of Bristol, Bristol, United Kingdom
| | - Roman Borisyuk
- School of Computing, Electronics and Mathematics, University of Plymouth, Plymouth, United Kingdom
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Sakurai A, Katz PS. The central pattern generator underlying swimming in Dendronotus iris: a simple half-center network oscillator with a twist. J Neurophysiol 2016; 116:1728-1742. [PMID: 27440239 DOI: 10.1152/jn.00150.2016] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Accepted: 07/14/2016] [Indexed: 11/22/2022] Open
Abstract
The nudibranch mollusc, Dendronotus iris, swims by rhythmically flexing its body from left to right. We identified a bilaterally represented interneuron, Si3, that provides strong excitatory drive to the previously identified Si2, forming a half-center oscillator, which functions as the central pattern generator (CPG) underlying swimming. As with Si2, Si3 inhibited its contralateral counterpart and exhibited rhythmic bursts in left-right alternation during the swim motor pattern. Si3 burst almost synchronously with the contralateral Si2 and was coactive with the efferent impulse activity in the contralateral body wall nerve. Perturbation of bursting in either Si3 or Si2 by current injection halted or phase-shifted the swim motor pattern, suggesting that they are both critical CPG members. Neither Si2 nor Si3 exhibited endogenous bursting properties when activated alone; activation of all four neurons was necessary to initiate and maintain the swim motor pattern. Si3 made a strong excitatory synapse onto the contralateral Si2 to which it is also electrically coupled. When Si3 was firing tonically but not exhibiting bursting, artificial enhancement of the Si3-to-Si2 synapse using dynamic clamp caused all four neurons to burst. In contrast, negation of the Si3-to-Si2 synapse by dynamic clamp blocked ongoing swim motor patterns. Together, these results suggest that the Dendronotus swim CPG is organized as a "twisted" half-center oscillator in which each "half" is composed of two excitatory-coupled neurons from both sides of the brain, each of which inhibits its contralateral counterpart. Consisting of only four neurons, this is perhaps the simplest known network oscillator for locomotion.
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Affiliation(s)
- Akira Sakurai
- Neuroscience Institute, Georgia State University, Atlanta, Georgia
| | - Paul S Katz
- Neuroscience Institute, Georgia State University, Atlanta, Georgia
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