Comparative morphology of the whiskers and faces of mice (Mus musculus) and rats (Rattus norvegicus)

Abstract

Understanding neural function requires quantification of the sensory signals that an animal's brain evolved to interpret. These signals in turn depend on the morphology and mechanics of the animal's sensory structures. Although the house mouse (Mus musculus) is one of the most common model species used in neuroscience, the spatial arrangement of its facial sensors has not yet been quantified. To address this gap, the present study quantifies the facial morphology of the mouse, with a particular focus on the geometry of its vibrissae (whiskers). The study develops equations that establish relationships between the three-dimensional (3D) locations of whisker basepoints, whisker geometry (arclength, curvature), and the 3D angles at which the whiskers emerge from the face. Additionally, the positions of facial sensory organs are quantified relative to bregma-lambda. Comparisons with the Norway rat (Rattus norvegicus) indicate that when normalized for head size, the whiskers of these two species have similar spacing density. The rostral-caudal distances between facial landmarks of the rat are a factor of ∼2.1 greater than the mouse, while the scale of bilateral distances is larger and more variable. We interpret these data to suggest that the larger size of rats compared to mice is a derived (apomorphic) trait. As rodents are increasingly important models in behavioral neuroscience, the morphological model developed here will help researchers generate naturalistic, multimodal patterns of stimulation for neurophysiological experiments and allow the generation of synthetic datasets and simulations to close the loop between brain, body, and environment.

A primary sensory cortical interareal feedforward inhibitory circuit for tacto-visual integration

“…However, it is important to acknowledge that realistic trajectories each whisker takes during protraction are still unknown, as current approaches for recording whisker movements in 3D space only provided trajectories for a subset of whiskers 40 . However, the whisker emergence angles observed in our simulations at the intermediate position closely align with recently reported angles for mouse whiskers 65 . This implies that the starting positions/orientations for simulated whisker protraction are based on realistic parameters.…”

“…Specifically, for a ventrally directed curvature of the whisker, ζ w was defined as 0°. Thus, for a dorsally directed curvature ζ w was defined as 180°, for a rostral directed curvature ζ w was 90° and for a caudally directed curvature ζ w was −90° 65 , 95 .…”