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Stable phase-shift despite quasi-rhythmic movements: a CPG-driven dynamic model of active tactile exploration in an insect.

Harischandra N, Krause AF, Dürr V - Front Comput Neurosci (2015)

Bottom Line: The effect of proprioceptor ablations could be simulated by changing the amplitude and offset parameters of the joint oscillators, only.We found that the phase-lead of the distal scape-pedicel (SP) joint relative to the proximal head-scape (HS) joint was essential for producing the natural tactile exploration behavior and, thus, for tactile efficiency.Based on our modeling results, we propose that a constant phase difference is coded into the CPG of the antennal motor system and that proprioceptors are acting locally to regulate the joint movement amplitude.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Cybernetics, Faculty of Biology, Bielefeld University Bielefeld, Germany ; Cognitive Interaction Technology Center of Excellence (CITEC), Bielefeld University Bielefeld, Germany.

ABSTRACT
An essential component of autonomous and flexible behavior in animals is active exploration of the environment, allowing for perception-guided planning and control of actions. An important sensory system involved is active touch. Here, we introduce a general modeling framework of Central Pattern Generators (CPGs) for movement generation in active tactile exploration behavior. The CPG consists of two network levels: (i) phase-coupled Hopf oscillators for rhythm generation, and (ii) pattern formation networks for capturing the frequency and phase characteristics of individual joint oscillations. The model captured the natural, quasi-rhythmic joint kinematics as observed in coordinated antennal movements of walking stick insects. Moreover, it successfully produced tactile exploration behavior on a three-dimensional skeletal model of the insect antennal system with physically realistic parameters. The effect of proprioceptor ablations could be simulated by changing the amplitude and offset parameters of the joint oscillators, only. As in the animal, the movement of both antennal joints was coupled with a stable phase difference, despite the quasi-rhythmicity of the joint angle time courses. We found that the phase-lead of the distal scape-pedicel (SP) joint relative to the proximal head-scape (HS) joint was essential for producing the natural tactile exploration behavior and, thus, for tactile efficiency. For realistic movement patterns, the phase-lead could vary within a limited range of 10-30° only. Tests with artificial movement patterns strongly suggest that this phase sensitivity is not a matter of the frequency composition of the natural movement pattern. Based on our modeling results, we propose that a constant phase difference is coded into the CPG of the antennal motor system and that proprioceptors are acting locally to regulate the joint movement amplitude.

No MeSH data available.


Antennal tip trajectories and joint angle time courses of an intact animal. HS and SP joint angles are shown by red and blue curves, respectively. (A) Data of a real animal as measured by Krause et al. (2013). In (B), the CPG includes the pattern generators modeled according to frequency components of the real data. (C) Simulations with the dynamic model being driven by a simple triangular waveform for each joint. Box-Whisker plots show joint angle distribution and the 5-to-95 percentiles of the working range. For this and the following figures, angle values are given in degrees.
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Figure 3: Antennal tip trajectories and joint angle time courses of an intact animal. HS and SP joint angles are shown by red and blue curves, respectively. (A) Data of a real animal as measured by Krause et al. (2013). In (B), the CPG includes the pattern generators modeled according to frequency components of the real data. (C) Simulations with the dynamic model being driven by a simple triangular waveform for each joint. Box-Whisker plots show joint angle distribution and the 5-to-95 percentiles of the working range. For this and the following figures, angle values are given in degrees.

Mentions: Stick insects show persistent elliptical antennal movement trajectories during walking. Here, we developed a 3D dynamic model of the active tactile system of the insect for the investigation of antennal motor control. In a first set of experiments, we tested the suitability of a purely CPG-driven model for simulating the natural antennal movement pattern during walking. For this, Figure 3 shows a comparison of the antennal tip trajectories and corresponding joint angle time courses of a representative experimental trial (Figure 3A) and of the model, using two driving signals of the pattern formation network. In Figure 3B, the driving signal is composed according to the frequency characteristics of the experimental joint angle time courses (single trial model, Mc). In Figure 3C, a triangular waveform was used. The latter was chosen because it could be generated by the simplest Fourier series that still captured the fast changes in movement direction observed in the experimental data. Even though the natural antennal movement sequence clearly has rhythmic components, its rhythmicity is varying with respect to amplitude and frequency even within individual trials. Thus, it can be considered as a quasi-rhythmic movement. This quasi-rhythmicity cannot be simulated with a constant triangular driving signal. On the other hand, the similarity of Figures 3A,B show that our model can indeed simulate experimental data quite well if the pattern formation network generates a sufficiently complex driving signal to the rhythm generating network. Note that due to the similarity in searching pattern in both antennae, only cases for the left antenna are shown in Figure 3 and the following figures.


Stable phase-shift despite quasi-rhythmic movements: a CPG-driven dynamic model of active tactile exploration in an insect.

Harischandra N, Krause AF, Dürr V - Front Comput Neurosci (2015)

Antennal tip trajectories and joint angle time courses of an intact animal. HS and SP joint angles are shown by red and blue curves, respectively. (A) Data of a real animal as measured by Krause et al. (2013). In (B), the CPG includes the pattern generators modeled according to frequency components of the real data. (C) Simulations with the dynamic model being driven by a simple triangular waveform for each joint. Box-Whisker plots show joint angle distribution and the 5-to-95 percentiles of the working range. For this and the following figures, angle values are given in degrees.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4543877&req=5

Figure 3: Antennal tip trajectories and joint angle time courses of an intact animal. HS and SP joint angles are shown by red and blue curves, respectively. (A) Data of a real animal as measured by Krause et al. (2013). In (B), the CPG includes the pattern generators modeled according to frequency components of the real data. (C) Simulations with the dynamic model being driven by a simple triangular waveform for each joint. Box-Whisker plots show joint angle distribution and the 5-to-95 percentiles of the working range. For this and the following figures, angle values are given in degrees.
Mentions: Stick insects show persistent elliptical antennal movement trajectories during walking. Here, we developed a 3D dynamic model of the active tactile system of the insect for the investigation of antennal motor control. In a first set of experiments, we tested the suitability of a purely CPG-driven model for simulating the natural antennal movement pattern during walking. For this, Figure 3 shows a comparison of the antennal tip trajectories and corresponding joint angle time courses of a representative experimental trial (Figure 3A) and of the model, using two driving signals of the pattern formation network. In Figure 3B, the driving signal is composed according to the frequency characteristics of the experimental joint angle time courses (single trial model, Mc). In Figure 3C, a triangular waveform was used. The latter was chosen because it could be generated by the simplest Fourier series that still captured the fast changes in movement direction observed in the experimental data. Even though the natural antennal movement sequence clearly has rhythmic components, its rhythmicity is varying with respect to amplitude and frequency even within individual trials. Thus, it can be considered as a quasi-rhythmic movement. This quasi-rhythmicity cannot be simulated with a constant triangular driving signal. On the other hand, the similarity of Figures 3A,B show that our model can indeed simulate experimental data quite well if the pattern formation network generates a sufficiently complex driving signal to the rhythm generating network. Note that due to the similarity in searching pattern in both antennae, only cases for the left antenna are shown in Figure 3 and the following figures.

Bottom Line: The effect of proprioceptor ablations could be simulated by changing the amplitude and offset parameters of the joint oscillators, only.We found that the phase-lead of the distal scape-pedicel (SP) joint relative to the proximal head-scape (HS) joint was essential for producing the natural tactile exploration behavior and, thus, for tactile efficiency.Based on our modeling results, we propose that a constant phase difference is coded into the CPG of the antennal motor system and that proprioceptors are acting locally to regulate the joint movement amplitude.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Cybernetics, Faculty of Biology, Bielefeld University Bielefeld, Germany ; Cognitive Interaction Technology Center of Excellence (CITEC), Bielefeld University Bielefeld, Germany.

ABSTRACT
An essential component of autonomous and flexible behavior in animals is active exploration of the environment, allowing for perception-guided planning and control of actions. An important sensory system involved is active touch. Here, we introduce a general modeling framework of Central Pattern Generators (CPGs) for movement generation in active tactile exploration behavior. The CPG consists of two network levels: (i) phase-coupled Hopf oscillators for rhythm generation, and (ii) pattern formation networks for capturing the frequency and phase characteristics of individual joint oscillations. The model captured the natural, quasi-rhythmic joint kinematics as observed in coordinated antennal movements of walking stick insects. Moreover, it successfully produced tactile exploration behavior on a three-dimensional skeletal model of the insect antennal system with physically realistic parameters. The effect of proprioceptor ablations could be simulated by changing the amplitude and offset parameters of the joint oscillators, only. As in the animal, the movement of both antennal joints was coupled with a stable phase difference, despite the quasi-rhythmicity of the joint angle time courses. We found that the phase-lead of the distal scape-pedicel (SP) joint relative to the proximal head-scape (HS) joint was essential for producing the natural tactile exploration behavior and, thus, for tactile efficiency. For realistic movement patterns, the phase-lead could vary within a limited range of 10-30° only. Tests with artificial movement patterns strongly suggest that this phase sensitivity is not a matter of the frequency composition of the natural movement pattern. Based on our modeling results, we propose that a constant phase difference is coded into the CPG of the antennal motor system and that proprioceptors are acting locally to regulate the joint movement amplitude.

No MeSH data available.