The Mechanics of Carpal Vibrissae of Rattus Norvegicus during Substrate Contact

Sinus hairs are tactile hairs of mammals, commonly also known as vibrissae or whiskers. The term “whisker” contemplates to the mystacial sinus hairs (mSH) in specific, which are situated around the snout of the animal. These mystacial sinus hairs can be moved actively to support and control sensing [1, 29]. The cyclic motion (whisking) of the mystacial sinus hairs was eponymous. In many species not only mSH can be found. Studies have demonstrated a variety of sinus hairs at multiple locations on the body surfaces of mammals [13, 27]. This contribution deals with carpal sinus hairs (cSH) at the forelimbs of rats. Although known for over 120 years – cSH first were discovered in some lemurs at the end of the 19 century [2, 5] – the knowledge of structure and function of cSH in mammals is very sparse in comparison to mSH. Carpal sinus hairs gain increasing interest since there is evidence on influences on the kinematics of the segmental chains of legs. One hypothesis is that cSH signals serve to adjust the stiffness of legs and to prepare them for the contact with different substrates or irregularities in the substrate – a function interesting for robotic locomotion. Studies on the locomotion of animals allow examining the influence of tactile information on walking parameters when mystacial and/or carpal sinus hairs are absent. Due to their small size it is very difficult to visualize the mechanical behavior of cSH during natural movement of a living rat with conventional methods. Therefore, we are proposing the use of a so called pedipulator – a mechanical gearing device which guides a dissected forelimb of a rat artificially on a natural trajectory. This approach shall help to understand the functionality of cSH and to interpret results from previous motions studies with living rats. Index Terms – sinus hair · vibrissae · carpal · locomotion · mechanics · pedipulation · touch