Vibrissal behavior and function
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Author: Prof. Tony J. Prescott, Dept Psychology, Univ of Sheffield, UK
Dr. Tony J. Prescott accepted the invitation on 20 February 2008 (self-imposed deadline: 20 December 2008).
This article will cover: overview of vibrissal behavior and function; behavioral evidence concerning the function of whiskers in rat behavior; development of vibrissal function; sensory modulation of whisking behavior; task-related differences in whisking behavior.
Contents |
Overview
Tactile hair, or vibrissae, are found on nearly all mammals except humans (Ahl, 1986). Vibrissae are found on various parts of the body, but those most studied are the facial or mystacial vibrissae, also called whiskers. Long facial whiskers, or macrovibrissae, are found in many mammalian species, projecting outwards and forwards from the snout of the animal to form a tactile sensory array that surrounds the head. For instance, in rats, the macrovibrissae form a two-dimensional grid of five rows on each side of the snout, each row containing between five and nine whiskers ranging between ~15 and ~50mm in length. These whiskers are continuously moving and actively controlled, being swept back and forth, at rates of up to twenty-five “whisks” per second with the forward movement of each whisker partially determined by its own intrinsic muscle (see Whisking Kinematics). Movements of the whiskers are also closely co-ordinated with those of the head and body allowing the animal to locate interesting stimuli through whisker contact, then investigate them further using both the macrovibrissae and an array of shorter, non-actuated microvibrissae on the chin and lips.
Brecht (1997) has provided a comparative morphological analysis of vibrissae systems in ten mammalian species including examples from marsupials, rodents, insectivores, pinnipeds, and primates, concluding that the presence of multiple rows of macrovibrissae increasing in length along the rostrocaudal axis, and of both macro- and micro- vibrissal arrays, are shared features of mammalian vibrissal sensing systems. Whisking, the repetitive independent movement of the vibrissae, is observed in a substantial sub-set of animals possessing prominent macrovibrissae. Other whisking rodents, in addition to rats, include mice, gerbils, chinchillas, hamsters and flying squirrels (Welker, 1964). However, there are several rodent genera that do not appear to whisk including guinea pigs, capybara, and gophers. Whisking behaviour has not been observed in carnivores (e.g. cats, dogs, racoons, pandas), although some families, such as pinnipeds (seals and walruses) have well-developed sinus muscles making the whiskers highly mobile.
The remainder of this article focuses the rat vibrissal system.
Behavioral evidence of vibrissal function
Experiments in adult rats involving whisker clipping, cauterization of the whisker follicle, section of the peripheral nerves, or lesion of critical structures in the vibrissal pathway, using appropriate controls for other sensory modalities such as vision and olfaction, have found significant deficits in a variety of behaviors including: surface discrimination, locating and orienting to stimuli, distance estimation and gap-crossing, thigmotaxis, exploration, maintenance of equilibrium, maze learning, swimming, predation, and fighting. Adults in which whiskers have been removed also show alterations of posture that have the effect of bringing the snout (and whisker stubs) into contact with surfaces of interest, whilst animals in which whiskers are plucked shortly after birth and repeatedly thereafter show pronounced behavioural compensations as adults.
Development of vibrissal function
Role of whisking in vibrissal function
Since rapid movement of the vibrissae consumes energy, it can be assumed that this conveys some sensory advantages to whisking animals. Likely benefits are that it: provides more degrees of freedom for sensor positioning, allows the animal to sample a larger volume of space with a given density of whiskers, and allows control over the velocity with which the whiskers contact surfaces. In addition, the ability to employ alternative whisking strategies in different contexts, may constitute an important gain. In other words, rats may “whisk” for the same reason that people carefully and continuously adjust the position of their fingertips whilst exploring objects with their hands, and adopt different exploratory strategies depending on the type of tactile judgement they are seeking to make (see Haptic Exploration). In both vibrissal and fingertip touch, then, better quality and more appropriate tactile information may be obtained by exerting precise control over how the sensory apparatus interacts with the world.
Sensory modulation of whisking behavior
Task-related differences in whisking behavior
| Invited by: | Prof. Tony J. Prescott, Dept Psychology, Univ of Sheffield, UK |
