Understanding how elephants use their trunk – sciencedaily
The elephant trunk (trunk) exhibits extraordinary kinematic versatility as it can handle a single blade of grass but also carry loads of up to 270 kilograms. Using motion capture technologies developed for the film industry, a team of scientists from the University of Geneva (UNIGE), Switzerland, demonstrate that the complex behaviors of the elephant trunk emerge from the combination of ‘a finite set of basic movements such as the propagation of an inward curvature and the formation of pseudo-joints. In addition, the Swiss team demonstrates that the speed of the elephant’s trunk obeys a mathematical law observed in the drawing movements of the human hand. These results are published in the journal Current biology.
Articulated bodies like the human skeleton are made up of joints in series, limiting the number of possible movements they can perform. Conversely, the elephant’s trunk is flexible over its entire length: the coordinated contractions of the muscles result in twisting, bending, lengthening, shortening and stiffening, without any bone support. These changes in shape rely on the constant volume of the self-supporting tissues of the tube, allowing a much greater variety of movement compared to the articulated appendages. Therefore, understanding how the elephant handles this complexity and manages to control the movement of its trunk is a difficult problem. To study this question, a multidisciplinary team led by Michel Milinkovitch, professor in the Department of Genetics and Evolution of the Faculty of Sciences at UNIGE and group leader at the Swiss Institute of Bioinformatics SIB, combined behavioral and motion capture with artistic medical imagery.
From Gollum to the elephant’s trunk
First, the researchers placed reflective markers along the trunks of two adult African elephants and recorded their trajectories in 3D with great precision using several infrared cameras positioned around the scene. This technology is borrowed from the film industry: Gollum in The Lord of the Rings or Na’vis in Avatar were brought to life by translating the movements of actors wearing motion capture markers to digitally created characters. The solution is to simplify
The Swiss team is now showing that elephants use a fundamental principle of simplification: sophisticated trunk trajectories are composed using a language of kinematic bricks. Indeed, the researchers identified a toolkit of about 20 basic simple movements (the equivalent of our words) that are combined by the trunk to produce a specific complex behavior, in the same way that a complex sentence is. made up of the combination of words. The items selected and combined depend on the task performed by the elephant. “When gripping and securing an object for transport, the proboscis exhibits localized flexion from its tip to its most basal parts, while when the elephant reaches a target in front of it, it extends and retracts specific parts of his trunk in a modular fashion, ”explains Paule Dagenais, researcher in the Milinkovitch team. The variation of the attributes of the objects induced transitions in the gripping strategies corresponding to different combinations of the 20 bricks. For example, when gripping a light wooden disc, the animal uses suction as a lifting force. On the other hand, suction is only used to secure the position of a heavier (metallic) disc while the trunk is wrapped around it to strengthen the grip.
Virtual joints, a mysterious mathematical law and biomimicry
When the target is placed more to the side, the strategy for reaching elephants is very particular: the continuous trunk forms rigid segments connected by virtual joints, momentarily giving the impression of an elbow and a wrist. “Further, we discovered that how much the trunk slows down when following a curve can be accurately predicted based on the local curvature of that path; remarkably, such a mathematical relationship between speed and curvature of the path also exists. for the human hand when drawing “, continues Michel Milinkovitch. Finally, using advanced computed tomography (CT), magnetic resonance imaging (MRI) and serial sections, the Swiss team characterized the anatomy African and Asian elephant trunks in unprecedented detail By analyzing these anatomical data in light of behavioral and kinematic results, the researchers were able to establish a strong link between the trunk muscular system and its biomechanical functions.
All of these results will serve as the basis for the development of a new concept of gentle robotic manipulation that would allow bio-inspired robots to sense, reach, grip, manipulate and release a whole range of payloads and objects of different shapes and sizes.
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