Strategy Change in Vibrissal Active Sensing during Rat Locomotion

During exploration, rats and other small mammals make rhythmic back-and-forth sweeps of their long facial whiskers (macrovibrissae) [1, 2 and 3]. These “whisking” movements are modulated by head movement [4] and by vibrissal sensory input [5 and 6] and hence are often considered “active” in the Gibsonian sense of being purposive and information seeking [7 and 8]. An important hallmark of active sensing is the modification of the control strategy according to context [9]. Using a task in which rats were trained to run circuits for food, we tested the hypothesis that whisker control, as measured by high-speed videography, changes with contextual variables such as environment familiarity, risk of collision, and availability of visual cues. In novel environments, functionally blind rats moved at slow speeds and performed broad whisker sweeps. With greater familiarity, however, they moved more rapidly, protracted their whiskers further, and showed decreased whisking amplitude. These findings indicate a strategy change from using the vibrissae to explore nearby surfaces to using them primarily for “look ahead.” In environments with increased risk of collision, functionally blind animals moved more slowly but protracted their whiskers further. Sighted animals also showed changes in whisker control strategy with increased familiarity, but these changes were different to those of the functionally blind strain. Sighted animals also changed their vibrissal behavior when visual cues were subsequently removed (by being placed in darkness). These contextual influences provide strong evidence of active control and demonstrate that the vibrissal system provides an accessible model of purposive behavior in mammals

Whisker touch guides canopy exploration in a nocturnal, arboreal rodent, the Hazel dormouse (Muscardinus avellanarius)

Dormouse numbers are declining in the UK due to habitat loss and fragmentation. We know that dormice are nocturnal, arboreal, and avoid crossing open spaces between habitats, yet how they navigate around their canopy is unknown. As other rodents use whisker touch sensing to navigate and explore their environment, this study investigates whether Hazel dormice (Muscardinus avellanarius) employ their whiskers to cross between habitats. We analysed high-speed video footage of dormice exploring freely in flat and climbing arenas in near darkness and using infrared light illumination. We confirm that, like rats and mice, dormice move their whiskers back and forth continuously (~10 Hz) in a motion called whisking and recruit them to explore small gaps (<10 cm) by increasing the amplitude and frequency of whisking and also the asymmetry of movement between the left and right whisker fields. When gaps between platforms are larger than 10-15 cm dormice spend more time travelling on the floor. These findings suggest that dormice can actively and purposively move their whiskers to gather relevant information from their canopy at night. As this species is vulnerable to threats on the ground, we also provide evidence that joining habitat patches between dormouse populations is important for promoting natural behaviours and movement between patches