California sea lions employ task-specific strategies for active touch sensing

Describing the musculature of mystacial pads in harbour seals (Phoca vitulina) using diceCT

Pinnipeds have long, sensitive, moveable mystacial vibrissae. In other mammals, intrinsic muscles contribute to protracting the vibrissae. However, the mystacial muscles of pinnipeds have not yet been systematically described. Using traditional histological methods provides us with two-dimensional muscle images, but having the ability to visualise these structures in three dimensions would allow for a more comprehensive understanding of pinniped vibrissal anatomy, especially given the challenges posed by their large and extremely curved mystacial pad. We predicted that harbour seals would have large, regular intrinsic muscles due to their well-organised, moveable vibrissae. We adopted diffusible iodine contrast-enhanced computer tomography (diceCT) to describe, for the first time, the three-dimensional architecture of the mystacial vibrissal muscles found in harbour seals. Our observations show that their vibrissae are organised into grids within the mystacial pad. We identified both sling-shaped and oblique intrinsic muscles that connect one vibrissae to the next in the same row. We also identified extrinsic muscles, including the m. nasolabialis, m. maxillolabialis, m. levator nasolabialis and m. orbicularis oris. Contrary to our prediction, the intrinsic muscles were not very large, although they were regularly distributed throughout the pad. Rather, the extrinsic muscles, particularly the m. nasolabialis and m. maxillolabialis were large, deep and well-defined, running throughout the length of the mystacial pad. Therefore, we suggest that these extrinsic muscles, the m. nasolabialis and m. maxillolabialis, are responsible for driving vibrissal protraction underwater. These findings demonstrate the importance of three-dimensional visualisation techniques in advancing our understanding of mystacial anatomy and function in pinnipeds.

Haptic Perception and Its Relation to Action

Haptic perception uses signals from touch receptors to detect, locate, and mentally represent objects and surfaces. Research from behavioral science, neuroscience, and computational modeling advances understanding of these essential functions. Haptic perception is grounded in neural circuitry that transmits external contact to the brain via increasingly abstracted representations. Computational models of mechanical interactions at the skin predict peripheral neural firing rates that initiate the processing chain. Behavioral phenomena and associated neural processes illustrate the reciprocal relationship by which perception supports action and action gates experience. The interaction of sensation and action is evident in how features of surfaces and objects such as softness and curvature are encoded. By incorporating touch sensations in conjunction with motor control, biologically embedded prosthetics enhance user capabilities and may elicit feelings of ownership. Efforts to create virtual haptic experience with advanced technologies underscore the complexity of this fundamental perceptual channel and its relation to action.

Demonstrating a measurement protocol for studying comparative whisker movements with implications for the evolution of behaviour

BACKGROUND

Studying natural, complex behaviours over a range of different species provides insights into the evolution of the brain and behaviour. Whisker movements reveal complex behaviours; however, there does not yet exist a protocol that is able to capture whisker movements and behaviours in a range of different species.

NEW METHOD

We develop a new protocol and make recommendations for measuring comparative whisker movements and behaviours. Using two set-ups - an enclosure camera set-up and a high-speed video set-up - we capture and measure the whisker movements of sixteen different captive mammal species from four different animal collections.

RESULTS

We demonstrate the ability to describe whisker movements and behaviours across a wide range of mammalian species. We describe whisker movements in European hedgehog, Cape porcupine, domestic rabbit, domestic ferret, weasel, European otter and red fox for the first time. We observe whisker movements in all the species we tested, although movement, positions and behaviours vary in a species-specific way.

COMPARISON WITH EXISTING METHOD(S)

The high-speed video set-up is based on the protocols of previous studies. The addition of an enclosure video set-up is entirely new, and allows us to include more species, especially large and shy species that cannot be moved into a high-speed filming arena.

CONCLUSIONS

We make recommendations for comparative whisker behaviour studies, particularly incorporating individual and species-specific considerations. We believe that flexible, comparative behavioural protocols have wide-ranging applications, specifically to better understand links between the brain and complex behaviours.