Self-recognition mechanism between skin and suckers prevents octopus arms from interfering with each other.
Controlling movements of flexible arms is a challenging task for the octopus because of the virtually infinite number of degrees of freedom (DOFs) [1, 2]. Octopuses simplify this control by using stereotypical motion patterns that reduce the DOFs, in the control space, to a workable few [2]. These movements are triggered by the brain and are generated by motor programs embedded in the peripheral neuromuscular system of the arm [3-5]. The hundreds of suckers along each arm have a tendency to stick to almost any object they contact [6-9]. The existence of this reflex could pose significant problems with unplanned interactions between the arms if not appropriately managed. This problem is likely to be accentuated because it is accepted that octopuses are "not aware of their arms" [10-14]. Here we report of a self-recognition mechanism that has a novel role in motor control, restraining the arms from interfering with each other. We show that the suckers of amputated arms never attach to octopus skin because a chemical in the skin inhibits the attachment reflex of the suckers. The peripheral mechanism appears to be overridden by central control because, in contrast to amputated arms, behaving octopuses sometime grab amputated arms. Surprisingly, octopuses seem to identify their own amputated arms, as they treat arms of other octopuses like food more often than their own. This self-recognition mechanism is a novel peripheral component in the embodied organization of the adaptive interactions between the octopus's brain, body, and environment [15, 16].
Department of Neurobiology, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel; School of Marine Sciences, Ruppin Academic Center, Michmoret 40250, Israel.
Nir
N
Nesher
Department of Neurobiology, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel; The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel.
Guy
G
Levy
BioMimetic and Cognitive Robotics, Department of Psychology Brooklyn College, the City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, USA.
Frank W
FW
Grasso
Department of Neurobiology, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel; The Interdisciplinary Center for Neural Computation, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel. Electronic address: benny.hochner@mail.huji.ac.il.
Binyamin
B
Hochner
D000818:Animals; D005121:Extremities / Q000502:physiology*; D005247:Feeding Behavior; D009068:Movement; D049831:Octopodiformes / Q000502:physiology*; D011597:Psychomotor Performance; D012018:Reflex; D012867:Skin / Q000378:metabolism