Dynamic Model of the Octopus Arm. II. Control of Reaching Movements

Abstract

The dynamic model of the octopus arm described in the first paper of this 2-part series was used here to investigate the neural strategies used for controlling the reaching movements of the octopus arm. These are stereotypical extension movements used to reach toward an object. In the dynamic model, sending a simple propagating neural activation signal to contract all muscles along the arm produced an arm extension with kinematic properties similar to those of natural movements. Control of only 2 parameters fully specified the extension movement: the amplitude of the activation signal (leading to the generation of muscle force) and the activation traveling time (the time the activation wave takes to travel along the arm). We found that the same kinematics could be achieved by applying activation signals with different activation amplitudes all exceeding some minimal level. This suggests that the octopus arm could use minimal amplitudes of activation to generate the minimal muscle forces required for the production of the desired kinematics. Larger-amplitude signals would generate larger forces that increase the arm's stability against perturbations without changing the kinematic characteristics. The robustness of this phenomenon was demonstrated by examining activation signals with either a constant or a bell-shaped velocity profile. Our modeling suggests that the octopus arm biomechanics may allow independent control of kinematics and resistance to perturbation during arm extension movements.

Locomotion byAbdopus aculeatus(Cephalopoda: Octopodidae):walking the line between primary and secondary defenses

“…Although the nervous control of locomotion is poorly understood, these single-arm movements do not necessarily require complex control. Nervous control of reaching is decentralized and can proceed without involvement of the brain's motor control region [the peduncle lobe (Messenger, 1967;Williamson and Chrachri, 2004)], allowing for simple feed-forward movements capable of incorporating feedback (Gutfreund et al, 1996;Gutfreund et al, 1998;Matzner et al, 2000;Sumbre et al, 2001;Yekutieli et al, 2005a;Yekutieli et al, 2005b).…”

Embodiment design of soft continuum robots

“…Researchers have investigated this behaviour by directly extracting the muscle contraction patterns from live octopus and externally applying these patterns to several octopus arm models. [30][31][32] It was then observed that the body dynamics may be used to control the arm's motion in a closed-loop manner by embedding nonlinear limit cycles. 8 However, the final step of bridging the gap between these findings and a robotic application was missing in previous works.…”

Octopus-inspired sensorimotor control of a multi-arm soft robot

“…Aside from integrating preprocessed visual input from the visual system, the relatively small CNS controls the highly autonomous PNS. The CNS has been shown to only send movement initiation signals to the PNS [24]. The PNS takes a large part of motor control function by embedded local motor programs [25].…”