Right–Left Asymmetries in the Whisking Behavior of Rats Anticipate Head Movements

Abstract

Rats use rhythmic movements of their vibrissae (whiskers) to tactually explore their environment. This "whisking" behavior has generally been reported to be strictly synchronous and symmetric about the snout, and it is thought to be controlled by a brainstem central pattern generator. Because the vibrissae can move independently of the head, however, maintaining a stable perception of the world would seem to require that rats adjust the bilateral symmetry of whisker movements in response to head movements. The present study used high-speed videography to reveal dramatic bilateral asymmetries and asynchronies in free-air whisking during head rotations. Kinematic analysis suggested that these asymmetric movements did not serve to maintain any fixed temporal relationship between right and left arrays, but rather to redirect the whiskers to a different region of space. More specifically, spatial asymmetry was found to be strongly correlated with rotational head velocity, ensuring a "look-ahead" distance of almost exactly one whisk. In contrast, bilateral asynchrony and velocity asymmetry were only weakly dependent on head velocity. Bilateral phase difference was found to be independent of the whisking frequency, suggesting the presence of two distinct left and right central pattern generators, connected as coupled oscillators. We suggest that the spatial asymmetries are analogous to the saccade that occurs during the initial portion of a combined head-eye gaze shift, and we begin to develop the rat vibrissal system as a new model for studying vestibular and proprioceptive contributions to the acquisition of sensory data.

Active vibrissal sensing in rodents and marsupials

“…0.40, p , 0.001) of the expected polarity (i.e. turning to the left predicted greater protraction on the right, see inset example in figure 4), but the magnitude of the response was consistently less strong in all species than that reported previously (coefficient of linearity is 28 to 35 compared with 115 in Towal & Hartmann [25]). Thus, while HTA is clearly expressed under conditions of free exploration, and in all tested species, the modulation may be less strong than in the tactile search paradigm employed in the original study.…”

“…Values close to zero indicate similar whisk amplitudes on the two sides of the snout, and positive/negative values biases towards the left/right sides of the animal. This value was compared with [25] for rat, but for the differences in experimental paradigm.…”

“…High-speed video recordings show that the whisker movements of freely moving animals often diverge from the regular, bilaterally symmetric and synchronous motor patterns that are usually seen in head-restrained animals. Asymmetries, asynchronies and changes in whisk amplitude and timing have been noted, some of which appear likely to boost the amount of useful sensory information obtained by the animal [6,9,16,25]. Forms of whisking modulation that can be considered to be elements of active sensing control include the following.…”

“…First, it has been shown that during tactile search behaviour, whisking tends to be biased towards the direction in which the animal is turning its head [25]. That is, as the head moves in space, whisking movements appear symmetric around the future orientation of the head and are consequently asymmetric with respect to the current head orientation.…”

Biomechanics of the Vibrissa Motor Plant in Rat: Rhythmic Whisking Consists of Triphasic Neuromuscular Activity

“…Trained animals typically whisk for bouts of 1 s or more during which the vibrissae move predominantly in the horizontal plane (Bermejo et al, 2002) with great temporal regularity . Rhythmic whisking exhibits bilateral symmetry (Gao et al, 2001) in the absence of head movements (Towal and Hartmann, 2006) or contact with an object (Sachdev et al, 2003;Mitchinson et al, 2007). Thus, whisking may be described by a small number of possibly interdependent control parameters, which include frequency of whisking as well as amplitude and anteroposterior set point of both vibrissa and pad motion.…”