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The Journal of Neuroscience, August 23, 2006, 26(34):8838-8846; doi:10.1523/JNEUROSCI.0581-06.2006
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Behavioral/Systems/Cognitive
RightLeft Asymmetries in the Whisking Behavior of Rats Anticipate Head Movements
R. Blythe Towal1 and
Mitra J. Hartmann1,2
Departments of 1Biomedical Engineering and 2Mechanical Engineering, Northwestern University, Evanston, Illinois 60208-3107
Correspondence should be addressed to Dr. Mitra J. Hartmann, Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3107. Email: m-hartmann{at}northwestern.edu
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 headeye 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.
Key words: vibrissa; vestibular; trigeminal; sensorimotor; whiskers; central pattern generator
Received Dec. 20, 2005;
revised June 8, 2006;
accepted July 13, 2006.
Correspondence should be addressed to Dr. Mitra J. Hartmann, Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3107. Email: m-hartmann{at}northwestern.edu
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