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Volume 16, Number 22, Issue of November 15, 1996 pp. 7297-7307
Copyright ©1996 Society for Neuroscience

Organization of Octopus Arm Movements: A Model System for Studying the Control of Flexible Arms

Received May 30, 1996; revised Aug. 13, 1996; accepted Aug. 26, 1996.

Yoram Gutfreund¹, Tamar Flash², Yosef Yarom¹, Graziano Fiorito³, Idan Segev¹, and Binyamin Hochner¹

¹ Department of Neurobiology and Center for Neuronal Computation, Institute of Life Sciences, Hebrew University, Jerusalem 91904, Israel, ² Department of Applied Mathematics, The Weizmann Institute of Science, Rehovot 76100, Israel, and ³ Laboratorio di Neurobiologia, Stazione Zoologica ``A. Dohrn'' di Napoli, Napoli 80121, Italy

Octopus arm movements provide an extreme example of controlled movements of a flexible arm with virtually unlimited degrees of freedom. This study aims to identify general principles in the organization of these movements. Video records of the movements of Octopus vulgaris performing the task of reaching toward a target were studied. The octopus extends its arm toward the target by a wave-like propagation of a bend that travels from the base of the arm toward the tip. Similar bend propagation is seen in other octopus arm movements, such as locomotion and searching. The kinematics (position and velocity) of the midpoint of the bend in three-dimensional space were extracted using the direct linear transformation algorithm. This showed that the bend tends to move within a single linear plane in a simple, slightly curved path connecting the center of the animal's body with the target location. Approximately 70% of the reaching movements demonstrated a stereotyped tangential velocity profile. An invariant profile was observed when movements were normalized for velocity and distance. Two arms, extended together in the same behavioral context, demonstrated identical velocity profiles. The stereotyped features of the movements were also observed in spontaneous arm extensions (not toward an external target). The simple and stereotypic appearance of the bend trajectory suggests that the position of the bend in space and time is the controlled variable. We propose that this strategy reduces the immense redundancy of the octopus arm movements and hence simplifies motor control.

Key words: movement control; muscular-hydrostat; kinematics; octopus; cephalopods; motor program; flexible arm; arm extension; reaching movements

This article has been cited by other articles:

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