Octopuses use a human-like strategy to control precise point-to-point arm movements. Sumbre, G., Fiorito, G., Flash, T., & Hochner, B. Curr Biol, 16(8):767-72, 2006.
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One of the key problems in motor control is mastering or reducing the number of degrees of freedom (DOFs) through coordination. This problem is especially prominent with hyper-redundant limbs such as the extremely flexible arm of the octopus. Several strategies for simplifying these control problems have been suggested for human point-to-point arm movements. Despite the evolutionary gap and morphological differences, humans and octopuses evolved similar strategies when fetching food to the mouth. To achieve this precise point-to-point-task, octopus arms generate a quasi-articulated structure based on three dynamic joints. A rotational movement around these joints brings the object to the mouth . Here, we describe a peripheral neural mechanism-two waves of muscle activation propagate toward each other, and their collision point sets the medial-joint location. This is a remarkably simple mechanism for adjusting the length of the segments according to where the object is grasped. Furthermore, similar to certain human arm movements, kinematic invariants were observed at the joint level rather than at the end-effector level, suggesting intrinsic control coordination. The evolutionary convergence to similar geometrical and kinematic features suggests that a kinematically constrained articulated limb controlled at the level of joint space is the optimal solution for precise point-to-point movements.
@Article{Sumbre2006,
  author   = {Germ\'an Sumbre and Graziano Fiorito and Tamar Flash and Binyamin Hochner},
  journal  = {Curr Biol},
  title    = {Octopuses use a human-like strategy to control precise point-to-point arm movements.},
  year     = {2006},
  number   = {8},
  pages    = {767-72},
  volume   = {16},
  abstract = {One of the key problems in motor control is mastering or reducing
	the number of degrees of freedom (DOFs) through coordination. This
	problem is especially prominent with hyper-redundant limbs such as
	the extremely flexible arm of the octopus. Several strategies for
	simplifying these control problems have been suggested for human
	point-to-point arm movements. Despite the evolutionary gap and morphological
	differences, humans and octopuses evolved similar strategies when
	fetching food to the mouth. To achieve this precise point-to-point-task,
	octopus arms generate a quasi-articulated structure based on three
	dynamic joints. A rotational movement around these joints brings
	the object to the mouth . Here, we describe a peripheral neural mechanism-two
	waves of muscle activation propagate toward each other, and their
	collision point sets the medial-joint location. This is a remarkably
	simple mechanism for adjusting the length of the segments according
	to where the object is grasped. Furthermore, similar to certain human
	arm movements, kinematic invariants were observed at the joint level
	rather than at the end-effector level, suggesting intrinsic control
	coordination. The evolutionary convergence to similar geometrical
	and kinematic features suggests that a kinematically constrained
	articulated limb controlled at the level of joint space is the optimal
	solution for precise point-to-point movements.},
  doi      = {10.1016/j.cub.2006.02.069},
  keywords = {16631583},
}
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