Limits...
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.


CPG configuration and the 3D skeletal model. (A) The CPG network consists of two oscillators per antenna and a single neck oscillator. Coupling strengths and phase differences are denoted by wij and ϕij, respectively (see Table 1). HS and SP stand for head-scape and scape-pedicel. (B) Two snap shots of the simulator show the skeletal model of the stick insect head and antennal system. Note the non-orthogonal, slanted joint axes (white) for each antennal joint. Scape and pedicel+flagellum are the proximal and the distal segments of each antenna, respectively. The external coordinate system is shown in the inset. The local coordinate systems for each antennal joint are shown in red, with their origins being located at the corresponding joint position.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4543877&req=5

Figure 1: CPG configuration and the 3D skeletal model. (A) The CPG network consists of two oscillators per antenna and a single neck oscillator. Coupling strengths and phase differences are denoted by wij and ϕij, respectively (see Table 1). HS and SP stand for head-scape and scape-pedicel. (B) Two snap shots of the simulator show the skeletal model of the stick insect head and antennal system. Note the non-orthogonal, slanted joint axes (white) for each antennal joint. Scape and pedicel+flagellum are the proximal and the distal segments of each antenna, respectively. The external coordinate system is shown in the inset. The local coordinate systems for each antennal joint are shown in red, with their origins being located at the corresponding joint position.

Mentions: The skeletal model underlying the forward dynamics simulation comprises the prothorax, the head and the two antennae. Each modeled antenna is composed of two segments: the scape and the pedicel-flagellum. Due to the passive nature of the joint between the pedicel and the flagellum, they are lumped together as a single segment in the model. The segments are connected via hinge joints, each one with a slanted axis of rotation and one degree of freedom (DOF, see Figure 1B). The head is connected to the prothorax via a neck joint with a vertical hinge joint axis. As a result, the single DOF of the neck allows for yaw rotations in the horizontal plane, only. Real stick insects have at least one other DOF in the neck, that is pitch. Though detailed motion analysis of the neck joints have not been carried out yet, Theunissen et al. (2015) found that stick insects adjust head pitch during climbing, so as to contribute to head stabilization. Since head pitch does not appear to be very rhythmical, we neglected it in the present version of the skeletal model, in order to simplify the control scheme.


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)

CPG configuration and the 3D skeletal model. (A) The CPG network consists of two oscillators per antenna and a single neck oscillator. Coupling strengths and phase differences are denoted by wij and ϕij, respectively (see Table 1). HS and SP stand for head-scape and scape-pedicel. (B) Two snap shots of the simulator show the skeletal model of the stick insect head and antennal system. Note the non-orthogonal, slanted joint axes (white) for each antennal joint. Scape and pedicel+flagellum are the proximal and the distal segments of each antenna, respectively. The external coordinate system is shown in the inset. The local coordinate systems for each antennal joint are shown in red, with their origins being located at the corresponding joint position.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 1: CPG configuration and the 3D skeletal model. (A) The CPG network consists of two oscillators per antenna and a single neck oscillator. Coupling strengths and phase differences are denoted by wij and ϕij, respectively (see Table 1). HS and SP stand for head-scape and scape-pedicel. (B) Two snap shots of the simulator show the skeletal model of the stick insect head and antennal system. Note the non-orthogonal, slanted joint axes (white) for each antennal joint. Scape and pedicel+flagellum are the proximal and the distal segments of each antenna, respectively. The external coordinate system is shown in the inset. The local coordinate systems for each antennal joint are shown in red, with their origins being located at the corresponding joint position.
Mentions: The skeletal model underlying the forward dynamics simulation comprises the prothorax, the head and the two antennae. Each modeled antenna is composed of two segments: the scape and the pedicel-flagellum. Due to the passive nature of the joint between the pedicel and the flagellum, they are lumped together as a single segment in the model. The segments are connected via hinge joints, each one with a slanted axis of rotation and one degree of freedom (DOF, see Figure 1B). The head is connected to the prothorax via a neck joint with a vertical hinge joint axis. As a result, the single DOF of the neck allows for yaw rotations in the horizontal plane, only. Real stick insects have at least one other DOF in the neck, that is pitch. Though detailed motion analysis of the neck joints have not been carried out yet, Theunissen et al. (2015) found that stick insects adjust head pitch during climbing, so as to contribute to head stabilization. Since head pitch does not appear to be very rhythmical, we neglected it in the present version of the skeletal model, in order to simplify the control scheme.

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.