SUMMARYLocust can jump precisely to a target, yet they can also tumble during the trajectory. We ... more SUMMARYLocust can jump precisely to a target, yet they can also tumble during the trajectory. We propose two mechanisms that would allow the locust to control tumbling during the jump. The first is that prior to the jump, locusts adjust the pitch of their body to move the center of mass closer to the intended thrust vector. The second is that contraction of the dorsolongitudinal muscles during the jump will produce torques that counter the torque produced by thrust. We found that locusts increased their take-off angle as the initial body pitch increased, and that little tumbling occurred for jumps that observed this relationship. Simulations of locust jumping demonstrated that a pitch versus take-off angle relationship that minimized tumbling in simulated jumps was similar to the relationship observed in live locusts. Locusts were strongly biased to pitch head-upward, and performed dorsiflexions far more often than ventral flexions. The direction and magnitude of tumbling could be c...
The rectification properties of electrical synapses made by the segmental giant (SG) neurone of c... more The rectification properties of electrical synapses made by the segmental giant (SG) neurone of crayfish (Pacifastacus leniusculus) were investigated. The SG * To whom offprint requests to should be sent
The nervous systems of animals evolved to exert dynamic control of behavior in response to the ne... more The nervous systems of animals evolved to exert dynamic control of behavior in response to the needs of the animal and changing signals from the environment. To understand the mechanisms of dynamic control requires a means of predicting how individual neural and body elements will interact to produce the performance of the entire system. AnimatLab is a software tool that provides an approach to this problem through computer simulation. AnimatLab enables a computational model of an animal's body to be constructed from simple building blocks, situated in a virtual 3D world subject to the laws of physics, and controlled by the activity of a multicellular, multicompartment neural circuit. Sensor receptors on the body surface and inside the body respond to external and internal signals and then excite central neurons, while motor neurons activate Hill muscle models that span the joints and generate movement. AnimatLab provides a common neuromechanical simulation environment in which...
Welcome and Acknowledgements Welcome to CNS*2007! The international Computational Neuroscience me... more Welcome and Acknowledgements Welcome to CNS*2007! The international Computational Neuroscience meeting (CNS) has been a premier forum for presenting experimental and theoretical results exploring the biology of computation in the nervous system for the last 16 years. The meeting is organized by the Organization for Computational Neurosciences (OCNS), a non-profit organization governed by an international executive committee and board of directors. A separate program committee is responsible for the scientific program of the meeting. Participants at the meeting are from academia and industry. The meeting not only provides a venue for research presentation and discussion by senior scientists but actively offers a forum for promoting and supporting young scientists and students from around the world. Welcome to Toronto! This meeting is being held in Canada for the first time, and the timing has been coordinated with the first ever Canadian summer school in Computational Neuroscience (organized by André Longtin in Ottawa). This meeting is made possible by the contributions of many individuals. I would like to thank the administrative and computing staff at the Toronto Western Research Institute for their help and support. In particular, I would like to express my appreciation to Poonam Bains and Crystal Leverman, whose help was invaluable from the very early planning stages to the present. I would also like to thank the cadre of student helpers (Darrell, Ernest, Eunji, Jesse, Marija, Raquel, Tariq) as well as key people at various junctures (Fernanda Saraga, Mary Pugh, Martin Wojtowicz, Melanie Woodin). Finally, I would like to thank OCNS executive, board and program committee members for their advice and input in many ways. In particular, I am indebted to Ranu Jung, Bill Holmes and Linda Larson-Prior for their help and support regarding the multitude of small and large details that are involved in organizing such a meeting. Thank you all! We look forward to a scientifically exciting and fun time. And please do not hesitate to ask us local folk for any help you might need!-Frances
SUMMARYThe neural circuitry and biomechanics of kicking in locusts have been studied to understan... more SUMMARYThe neural circuitry and biomechanics of kicking in locusts have been studied to understand their roles in the control of both kicking and jumping. It has been hypothesized that the same neural circuit and biomechanics governed both behaviors but this hypothesis was not testable with current technology. We built a neuromechanical model to test this and to gain a better understanding of the role of the semi-lunar process (SLP) in jump dynamics. The jumping and kicking behaviors of the model were tested by comparing them with a variety of published data, and were found to reproduce the results from live animals. This confirmed that the kick neural circuitry can produce the jump behavior. The SLP is a set of highly sclerotized bands of cuticle that can be bent to store energy for use during kicking and jumping. It has not been possible to directly test the effects of the SLP on jump performance because it is an integral part of the joint, and attempts to remove its influence pre...
Cortical slices produce propagating waves when disinhibited or when treated with medium low in ma... more Cortical slices produce propagating waves when disinhibited or when treated with medium low in magnesium. The lowered magnesium unblocks the NMDA receptors allowing for long lasting synaptic depolarization. We describe two possible mechanisms for these oscillations: (i) depolarization block leading to an "elliptic burster" and (ii) after-hyperpolarization with persistent sodium leading to a "square-wave" burster. Predictions allowing us to distinguish these two possibilities are made.
1. The responses of the cockroach descending contralateral movement detector (DCMD) neurone to mo... more 1. The responses of the cockroach descending contralateral movement detector (DCMD) neurone to moving light stimuli were studied under both light- and dark-adapted conditions. 2. With light-adaptation the response of the DCMD to two moving 2° (diam.) spots of white light is less than the response to a single spot when the two spots are separated by less than 10° (Fig. 2). 3. With light-adaptation the response of the DCMD to a single moving light spot is a sigmoidally shaped function of the logarithm of the light intensity (Fig. 3a). With dark-adaptation the response of a DCMD to a single moving light spot is a bell-shaped function of the logarithm of the stimulus intensity (Fig. 3b). The absolute intensity that evokes a threshold response is about one-and-a-half log units less in the dark-adapted eye than in the light-adapted eye. 4. The decrease in the DCMD's response that occurs when two stimuli are closer than 10°, and when a single bright stimulus is made brighter, indicates...
Full list of author information is available at the end of the article Figure 1 Neuromechanical m... more Full list of author information is available at the end of the article Figure 1 Neuromechanical model. Body model is at left, showing thorax and left 5 th leg with hinges, CBCO stretch receptor, and Dep (red) and Lev (blue) muscles identified. Circuit is at right, with Dep MNs, INs, and muscles in red, and Lev in blue. Muscles and CBCO correspond to those shown in body diagram.
Creation of a dominance hierarchy within a population of animals typically involves a period of a... more Creation of a dominance hierarchy within a population of animals typically involves a period of agonistic activity in which winning and losing decide relative positions in the hierarchy. Among crayfish, fighting between size-matched animals leads to an abrupt change of behavior as the new subordinate retreats and escapes from the attacks and approaches of the dominant (Issa et al., 1999). We used high-speed videography and electrical recordings of aquarium field potentials to monitor the release of aggressive and defensive behavior, including the activation of neural circuits for four different tail-flip behaviors. We found that the sequence of tail-flip circuit excitation traced the development of their dominance hierarchy. Offensive tail flipping, attacks, and approaches by both animals were followed by a sharp rise in the frequency of nongiant and medial giant escape tail flips and a fall in the frequency of offensive tail flips of the new subordinate. These changes suggest that sudden, coordinated changes in the excitability of a set of neural circuits in one animal produce the changes in behavior that mark its transition to subordinate status.
The effect of superfused serotonin (5-HT; 50 M) on the synaptic responses of the lateral giant (L... more The effect of superfused serotonin (5-HT; 50 M) on the synaptic responses of the lateral giant (LG) interneuron in crayfish was found to depend on the social status of the animal. In socially isolated animals, 5-HT persistently increased the response of LG to sensory nerve shock. After social isolates were paired in a small cage, they fought and determined their dominant and subordinate status. After 12 d of pairing, 5-HT reversibly inhibited the response of LG in the social subordinate and reversibly increased the response of LG in the social dominant crayfish. The effect of 5-HT changed approximately linearly from response enhancement to inhibition in the new subordinate over the 12 d of pairing. If, after 12 d pairing, the subordinate was reisolated for 8 d, the response enhancement was restored. If the subordinate, instead, was paired with another subordinate and became dominant in this new pair, the inhibitory effect of 5-HT changed to an enhancing effect over the next 12 d of pairing. If, however, two dominant crayfish were paired and one became subordinate, the enhancing effect of 5-HT persisted in the new subordinate even after 38 d pairing. These different effects of serotonin result from the action of two or more molecular receptors for serotonin. A vertebrate 5-HT 1 agonist had no effect on social isolates but reversibly inhibited the response of LG in both dominant and subordinate crayfish. The inhibitory effects of the agonist developed approximately linearly over the first 12 d of pairing. A vertebrate 5-HT 2 agonist persistently increased the response of LG in isolate crayfish and reversibly increased the response of the cell in dominant and subordinate crayfish. Finally, although neurons that might mediate these effects of superfused 5-HT are unknown, one pair of 5-HT-immunoreactive neurons appears to contact the LG axon and initial axon segment in each abdominal ganglion in its projection caudally from the thorax.
Serotonin modulates afferent synaptic transmission to the lateral giant neurons of crayfish, whic... more Serotonin modulates afferent synaptic transmission to the lateral giant neurons of crayfish, which are command neurons for escape behavior. Low concentrations, or high concentrations reached gradually, are facilitatory, whereas high concentrations reached rapidly are inhibitory. The modulatory effects rapidly reverse after brief periods of application, whereas longer periods of application are followed by facilitation that persists for hours. These effects of serotonin can be reproduced by models that involve multiple interacting intracellular signaling systems that are each stimulated by serotonin. The dependence of the neuromodulatory effect on dose, rate, and duration of modulator application may be relevant to understanding the effects of natural neuromodulation on behavior and cognition and to the design of drug therapies.
Neuromechanical Modeling of Posture and Locomotion, 2015
Central pattern generators (CPGs) are oscillatory neuronal networks controlling rhythmic motor be... more Central pattern generators (CPGs) are oscillatory neuronal networks controlling rhythmic motor behaviors such as swimming, walking, and breathing. Multifunctional CPGs are capable of producing multiple patterns of rhythmic activity with different periods. Here, we investigate whether two cat rhythmic motor behaviors, walking and paw-shaking, could be controlled by a single multifunctional CPG. To do this, we have created a parsimonious model of a half-center oscillator composed of two mutually inhibitory neurons. Two basic activity regimes coexist in this model: fast 10 Hz paw-shake regime and a slow 2 Hz walking regime. It is possible to switch from paw-shaking to walking with a short pulse of conductance in one neuron, and it is possible to switch from walking to paw-shaking with a longer pulse of excitatory conductance in both neurons. The paw-shake and walking rhythms generated by the CPG model were used as input to a neuromechanical model of the cat hindlimbs to simulate the corresponding rhythmic behaviors. Simulation results demonstrated that the multifunctional half-center locomotor CPG could produce movement mechanics and muscle activity patterns typical for cat walking or paw-shake responses if synaptic weights in selected spinal circuits were altered during each behavior. We propose that the selection of CPG regimes and spinal circuitry is triggered by sensory input from paw skin afferents.
Herberholz et al. Micro-neuroimaging in crayfish ducted in the absence of any commercial or finan... more Herberholz et al. Micro-neuroimaging in crayfish ducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The social rank of an animal is distinguished by its behavior relative to others in its community... more The social rank of an animal is distinguished by its behavior relative to others in its community. Although social-status-dependent differences in behavior must arise because of differences in neural function, status-dependent differences in the underlying neural circuitry have only begun to be described. We report that dominant and subordinate crayfish differ in their behavioral orienting response to an unexpected unilateral touch, and that these differences correlate with functional differences in local neural circuits that mediate the responses. The behavioral differences correlate with simultaneously recorded differences in leg depressor muscle EMGs and with differences in the responses of depressor motor neurons recorded in reduced, in vitro preparations from the same animals. The responses of local serotonergic interneurons to unilateral stimuli displayed the same status-dependent differences as the depressor motor neurons. These results indicate that the circuits and their intrinsic serotonergic modulatory components are configured differently according to social status, and that these differences do not depend on a continuous descending signal from higher centers.
Lateral excitation is a mechanism for amplifying coordinated input to postsynaptic neurons that h... more Lateral excitation is a mechanism for amplifying coordinated input to postsynaptic neurons that has been described recently in several species. Here, we describe how a postsynaptic neuron, the lateral giant (LG) escape command neuron, enhances lateral excitation among its presynaptic mechanosensory afferents in the crayfish tailfan. A lateral excitatory network exists among electrically coupled tailfan primary afferents, mediated through central electrical synapses. EPSPs elicited in LG dendrites as a result of mechanosensory stimulation spread antidromically back through electrical junctions to unstimulated afferents, summate with EPSPs elicited through direct afferentto-afferent connections, and contribute to recruitment of these afferents. Antidromic potentials are larger if the afferent is closer to the initial input on LG dendrites, which could create a spatial filtering mechanism within the network. This pathway also broadens the temporal window over which lateral excitation can occur, because of the delay required for EPSPs to spread through the large LG dendrites. The delay allows subthreshold inputs to the LG to have a priming effect on the lateral excitatory network and lowers the threshold of the network in response to a second, short-latency stimulus. Retrograde communication within neuronal pathways has been described in a number of vertebrate and invertebrate species. A mechanism of antidromic passage of depolarizing current from a neuron to its presynaptic afferents, similar to that described here in an invertebrate, is also present in a vertebrate (fish). This raises the possibility that short-term retrograde modulation of presynaptic elements through electrical junctions may be common.
SUMMARY Crayfish fight and form a dominance hierarchy characterized by a pattern of repeated agon... more SUMMARY Crayfish fight and form a dominance hierarchy characterized by a pattern of repeated agonistic interactions between animals with a consistent outcome of winner and loser. Once a dominance hierarchy is established, dominant animals display an elevated posture with both claws held laterally and forward,whereas subordinate animals display a more prone posture with both claws extended forward and down. Dominant animals behave aggressively towards the subordinate opponent, often approaching and attacking, whereas subordinate animals behave submissively by tailflipping and retreating. To evaluate whether the differences in social behavior are accompanied by differences in responses to non-social stimuli, we exposed socially naïve and experienced crayfish (Procambarus clarkii) to an unexpected touch in different social conditions. Socially naïve animals turned to confront the source of a unilateral touch with raised claws and elevated posture. Dominant animals also turned to face...
SUMMARY The neural systems that control escape behavior have been studied intensively in several ... more SUMMARY The neural systems that control escape behavior have been studied intensively in several animals, including mollusks, fish and crayfish. Surprisingly little is known, however, about the activation and the utilization of escape circuits during prey–predator interactions. To complement the physiological and anatomical studies with a necessary behavioral equivalent, we investigated encounters between juvenile crayfish and large dragonfly nymphs in freely behaving animals using a combination of high-speed video-recordings and measurements of electric field potentials. During attacks, dragonfly nymphs rapidly extended their labium, equipped with short, sharp palps, to capture small crayfish. Crayfish responded to the tactile stimulus by activating neural escape circuits to generate tail-flips directed away from the predator. Tail-flips were the sole defense mechanism in response to an attack and every single strike was answered by tail-flip escape behavior. Crayfish used all thre...
Rostral ganglia are required for induction but not expression of crayfish escape reflex habituati... more Rostral ganglia are required for induction but not expression of crayfish escape reflex habituation: role of higher centers in reprogramming low-level circuits.
SUMMARYLocust can jump precisely to a target, yet they can also tumble during the trajectory. We ... more SUMMARYLocust can jump precisely to a target, yet they can also tumble during the trajectory. We propose two mechanisms that would allow the locust to control tumbling during the jump. The first is that prior to the jump, locusts adjust the pitch of their body to move the center of mass closer to the intended thrust vector. The second is that contraction of the dorsolongitudinal muscles during the jump will produce torques that counter the torque produced by thrust. We found that locusts increased their take-off angle as the initial body pitch increased, and that little tumbling occurred for jumps that observed this relationship. Simulations of locust jumping demonstrated that a pitch versus take-off angle relationship that minimized tumbling in simulated jumps was similar to the relationship observed in live locusts. Locusts were strongly biased to pitch head-upward, and performed dorsiflexions far more often than ventral flexions. The direction and magnitude of tumbling could be c...
The rectification properties of electrical synapses made by the segmental giant (SG) neurone of c... more The rectification properties of electrical synapses made by the segmental giant (SG) neurone of crayfish (Pacifastacus leniusculus) were investigated. The SG * To whom offprint requests to should be sent
The nervous systems of animals evolved to exert dynamic control of behavior in response to the ne... more The nervous systems of animals evolved to exert dynamic control of behavior in response to the needs of the animal and changing signals from the environment. To understand the mechanisms of dynamic control requires a means of predicting how individual neural and body elements will interact to produce the performance of the entire system. AnimatLab is a software tool that provides an approach to this problem through computer simulation. AnimatLab enables a computational model of an animal's body to be constructed from simple building blocks, situated in a virtual 3D world subject to the laws of physics, and controlled by the activity of a multicellular, multicompartment neural circuit. Sensor receptors on the body surface and inside the body respond to external and internal signals and then excite central neurons, while motor neurons activate Hill muscle models that span the joints and generate movement. AnimatLab provides a common neuromechanical simulation environment in which...
Welcome and Acknowledgements Welcome to CNS*2007! The international Computational Neuroscience me... more Welcome and Acknowledgements Welcome to CNS*2007! The international Computational Neuroscience meeting (CNS) has been a premier forum for presenting experimental and theoretical results exploring the biology of computation in the nervous system for the last 16 years. The meeting is organized by the Organization for Computational Neurosciences (OCNS), a non-profit organization governed by an international executive committee and board of directors. A separate program committee is responsible for the scientific program of the meeting. Participants at the meeting are from academia and industry. The meeting not only provides a venue for research presentation and discussion by senior scientists but actively offers a forum for promoting and supporting young scientists and students from around the world. Welcome to Toronto! This meeting is being held in Canada for the first time, and the timing has been coordinated with the first ever Canadian summer school in Computational Neuroscience (organized by André Longtin in Ottawa). This meeting is made possible by the contributions of many individuals. I would like to thank the administrative and computing staff at the Toronto Western Research Institute for their help and support. In particular, I would like to express my appreciation to Poonam Bains and Crystal Leverman, whose help was invaluable from the very early planning stages to the present. I would also like to thank the cadre of student helpers (Darrell, Ernest, Eunji, Jesse, Marija, Raquel, Tariq) as well as key people at various junctures (Fernanda Saraga, Mary Pugh, Martin Wojtowicz, Melanie Woodin). Finally, I would like to thank OCNS executive, board and program committee members for their advice and input in many ways. In particular, I am indebted to Ranu Jung, Bill Holmes and Linda Larson-Prior for their help and support regarding the multitude of small and large details that are involved in organizing such a meeting. Thank you all! We look forward to a scientifically exciting and fun time. And please do not hesitate to ask us local folk for any help you might need!-Frances
SUMMARYThe neural circuitry and biomechanics of kicking in locusts have been studied to understan... more SUMMARYThe neural circuitry and biomechanics of kicking in locusts have been studied to understand their roles in the control of both kicking and jumping. It has been hypothesized that the same neural circuit and biomechanics governed both behaviors but this hypothesis was not testable with current technology. We built a neuromechanical model to test this and to gain a better understanding of the role of the semi-lunar process (SLP) in jump dynamics. The jumping and kicking behaviors of the model were tested by comparing them with a variety of published data, and were found to reproduce the results from live animals. This confirmed that the kick neural circuitry can produce the jump behavior. The SLP is a set of highly sclerotized bands of cuticle that can be bent to store energy for use during kicking and jumping. It has not been possible to directly test the effects of the SLP on jump performance because it is an integral part of the joint, and attempts to remove its influence pre...
Cortical slices produce propagating waves when disinhibited or when treated with medium low in ma... more Cortical slices produce propagating waves when disinhibited or when treated with medium low in magnesium. The lowered magnesium unblocks the NMDA receptors allowing for long lasting synaptic depolarization. We describe two possible mechanisms for these oscillations: (i) depolarization block leading to an "elliptic burster" and (ii) after-hyperpolarization with persistent sodium leading to a "square-wave" burster. Predictions allowing us to distinguish these two possibilities are made.
1. The responses of the cockroach descending contralateral movement detector (DCMD) neurone to mo... more 1. The responses of the cockroach descending contralateral movement detector (DCMD) neurone to moving light stimuli were studied under both light- and dark-adapted conditions. 2. With light-adaptation the response of the DCMD to two moving 2° (diam.) spots of white light is less than the response to a single spot when the two spots are separated by less than 10° (Fig. 2). 3. With light-adaptation the response of the DCMD to a single moving light spot is a sigmoidally shaped function of the logarithm of the light intensity (Fig. 3a). With dark-adaptation the response of a DCMD to a single moving light spot is a bell-shaped function of the logarithm of the stimulus intensity (Fig. 3b). The absolute intensity that evokes a threshold response is about one-and-a-half log units less in the dark-adapted eye than in the light-adapted eye. 4. The decrease in the DCMD's response that occurs when two stimuli are closer than 10°, and when a single bright stimulus is made brighter, indicates...
Full list of author information is available at the end of the article Figure 1 Neuromechanical m... more Full list of author information is available at the end of the article Figure 1 Neuromechanical model. Body model is at left, showing thorax and left 5 th leg with hinges, CBCO stretch receptor, and Dep (red) and Lev (blue) muscles identified. Circuit is at right, with Dep MNs, INs, and muscles in red, and Lev in blue. Muscles and CBCO correspond to those shown in body diagram.
Creation of a dominance hierarchy within a population of animals typically involves a period of a... more Creation of a dominance hierarchy within a population of animals typically involves a period of agonistic activity in which winning and losing decide relative positions in the hierarchy. Among crayfish, fighting between size-matched animals leads to an abrupt change of behavior as the new subordinate retreats and escapes from the attacks and approaches of the dominant (Issa et al., 1999). We used high-speed videography and electrical recordings of aquarium field potentials to monitor the release of aggressive and defensive behavior, including the activation of neural circuits for four different tail-flip behaviors. We found that the sequence of tail-flip circuit excitation traced the development of their dominance hierarchy. Offensive tail flipping, attacks, and approaches by both animals were followed by a sharp rise in the frequency of nongiant and medial giant escape tail flips and a fall in the frequency of offensive tail flips of the new subordinate. These changes suggest that sudden, coordinated changes in the excitability of a set of neural circuits in one animal produce the changes in behavior that mark its transition to subordinate status.
The effect of superfused serotonin (5-HT; 50 M) on the synaptic responses of the lateral giant (L... more The effect of superfused serotonin (5-HT; 50 M) on the synaptic responses of the lateral giant (LG) interneuron in crayfish was found to depend on the social status of the animal. In socially isolated animals, 5-HT persistently increased the response of LG to sensory nerve shock. After social isolates were paired in a small cage, they fought and determined their dominant and subordinate status. After 12 d of pairing, 5-HT reversibly inhibited the response of LG in the social subordinate and reversibly increased the response of LG in the social dominant crayfish. The effect of 5-HT changed approximately linearly from response enhancement to inhibition in the new subordinate over the 12 d of pairing. If, after 12 d pairing, the subordinate was reisolated for 8 d, the response enhancement was restored. If the subordinate, instead, was paired with another subordinate and became dominant in this new pair, the inhibitory effect of 5-HT changed to an enhancing effect over the next 12 d of pairing. If, however, two dominant crayfish were paired and one became subordinate, the enhancing effect of 5-HT persisted in the new subordinate even after 38 d pairing. These different effects of serotonin result from the action of two or more molecular receptors for serotonin. A vertebrate 5-HT 1 agonist had no effect on social isolates but reversibly inhibited the response of LG in both dominant and subordinate crayfish. The inhibitory effects of the agonist developed approximately linearly over the first 12 d of pairing. A vertebrate 5-HT 2 agonist persistently increased the response of LG in isolate crayfish and reversibly increased the response of the cell in dominant and subordinate crayfish. Finally, although neurons that might mediate these effects of superfused 5-HT are unknown, one pair of 5-HT-immunoreactive neurons appears to contact the LG axon and initial axon segment in each abdominal ganglion in its projection caudally from the thorax.
Serotonin modulates afferent synaptic transmission to the lateral giant neurons of crayfish, whic... more Serotonin modulates afferent synaptic transmission to the lateral giant neurons of crayfish, which are command neurons for escape behavior. Low concentrations, or high concentrations reached gradually, are facilitatory, whereas high concentrations reached rapidly are inhibitory. The modulatory effects rapidly reverse after brief periods of application, whereas longer periods of application are followed by facilitation that persists for hours. These effects of serotonin can be reproduced by models that involve multiple interacting intracellular signaling systems that are each stimulated by serotonin. The dependence of the neuromodulatory effect on dose, rate, and duration of modulator application may be relevant to understanding the effects of natural neuromodulation on behavior and cognition and to the design of drug therapies.
Neuromechanical Modeling of Posture and Locomotion, 2015
Central pattern generators (CPGs) are oscillatory neuronal networks controlling rhythmic motor be... more Central pattern generators (CPGs) are oscillatory neuronal networks controlling rhythmic motor behaviors such as swimming, walking, and breathing. Multifunctional CPGs are capable of producing multiple patterns of rhythmic activity with different periods. Here, we investigate whether two cat rhythmic motor behaviors, walking and paw-shaking, could be controlled by a single multifunctional CPG. To do this, we have created a parsimonious model of a half-center oscillator composed of two mutually inhibitory neurons. Two basic activity regimes coexist in this model: fast 10 Hz paw-shake regime and a slow 2 Hz walking regime. It is possible to switch from paw-shaking to walking with a short pulse of conductance in one neuron, and it is possible to switch from walking to paw-shaking with a longer pulse of excitatory conductance in both neurons. The paw-shake and walking rhythms generated by the CPG model were used as input to a neuromechanical model of the cat hindlimbs to simulate the corresponding rhythmic behaviors. Simulation results demonstrated that the multifunctional half-center locomotor CPG could produce movement mechanics and muscle activity patterns typical for cat walking or paw-shake responses if synaptic weights in selected spinal circuits were altered during each behavior. We propose that the selection of CPG regimes and spinal circuitry is triggered by sensory input from paw skin afferents.
Herberholz et al. Micro-neuroimaging in crayfish ducted in the absence of any commercial or finan... more Herberholz et al. Micro-neuroimaging in crayfish ducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The social rank of an animal is distinguished by its behavior relative to others in its community... more The social rank of an animal is distinguished by its behavior relative to others in its community. Although social-status-dependent differences in behavior must arise because of differences in neural function, status-dependent differences in the underlying neural circuitry have only begun to be described. We report that dominant and subordinate crayfish differ in their behavioral orienting response to an unexpected unilateral touch, and that these differences correlate with functional differences in local neural circuits that mediate the responses. The behavioral differences correlate with simultaneously recorded differences in leg depressor muscle EMGs and with differences in the responses of depressor motor neurons recorded in reduced, in vitro preparations from the same animals. The responses of local serotonergic interneurons to unilateral stimuli displayed the same status-dependent differences as the depressor motor neurons. These results indicate that the circuits and their intrinsic serotonergic modulatory components are configured differently according to social status, and that these differences do not depend on a continuous descending signal from higher centers.
Lateral excitation is a mechanism for amplifying coordinated input to postsynaptic neurons that h... more Lateral excitation is a mechanism for amplifying coordinated input to postsynaptic neurons that has been described recently in several species. Here, we describe how a postsynaptic neuron, the lateral giant (LG) escape command neuron, enhances lateral excitation among its presynaptic mechanosensory afferents in the crayfish tailfan. A lateral excitatory network exists among electrically coupled tailfan primary afferents, mediated through central electrical synapses. EPSPs elicited in LG dendrites as a result of mechanosensory stimulation spread antidromically back through electrical junctions to unstimulated afferents, summate with EPSPs elicited through direct afferentto-afferent connections, and contribute to recruitment of these afferents. Antidromic potentials are larger if the afferent is closer to the initial input on LG dendrites, which could create a spatial filtering mechanism within the network. This pathway also broadens the temporal window over which lateral excitation can occur, because of the delay required for EPSPs to spread through the large LG dendrites. The delay allows subthreshold inputs to the LG to have a priming effect on the lateral excitatory network and lowers the threshold of the network in response to a second, short-latency stimulus. Retrograde communication within neuronal pathways has been described in a number of vertebrate and invertebrate species. A mechanism of antidromic passage of depolarizing current from a neuron to its presynaptic afferents, similar to that described here in an invertebrate, is also present in a vertebrate (fish). This raises the possibility that short-term retrograde modulation of presynaptic elements through electrical junctions may be common.
SUMMARY Crayfish fight and form a dominance hierarchy characterized by a pattern of repeated agon... more SUMMARY Crayfish fight and form a dominance hierarchy characterized by a pattern of repeated agonistic interactions between animals with a consistent outcome of winner and loser. Once a dominance hierarchy is established, dominant animals display an elevated posture with both claws held laterally and forward,whereas subordinate animals display a more prone posture with both claws extended forward and down. Dominant animals behave aggressively towards the subordinate opponent, often approaching and attacking, whereas subordinate animals behave submissively by tailflipping and retreating. To evaluate whether the differences in social behavior are accompanied by differences in responses to non-social stimuli, we exposed socially naïve and experienced crayfish (Procambarus clarkii) to an unexpected touch in different social conditions. Socially naïve animals turned to confront the source of a unilateral touch with raised claws and elevated posture. Dominant animals also turned to face...
SUMMARY The neural systems that control escape behavior have been studied intensively in several ... more SUMMARY The neural systems that control escape behavior have been studied intensively in several animals, including mollusks, fish and crayfish. Surprisingly little is known, however, about the activation and the utilization of escape circuits during prey–predator interactions. To complement the physiological and anatomical studies with a necessary behavioral equivalent, we investigated encounters between juvenile crayfish and large dragonfly nymphs in freely behaving animals using a combination of high-speed video-recordings and measurements of electric field potentials. During attacks, dragonfly nymphs rapidly extended their labium, equipped with short, sharp palps, to capture small crayfish. Crayfish responded to the tactile stimulus by activating neural escape circuits to generate tail-flips directed away from the predator. Tail-flips were the sole defense mechanism in response to an attack and every single strike was answered by tail-flip escape behavior. Crayfish used all thre...
Rostral ganglia are required for induction but not expression of crayfish escape reflex habituati... more Rostral ganglia are required for induction but not expression of crayfish escape reflex habituation: role of higher centers in reprogramming low-level circuits.
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