Whisker deafferentation and rodent whisking patterns: Behavioral evidence for a central pattern generator

Even in the absence of explicit stimulation, rats emit patterns of rhythmic whisking movements. Because of their stereotyped nature and their persiste nce after sensory denervation and cortical ablation, whisking movements hav e been assumed to reflect the output of a central pattern generator (CPG). However, identification of a movement pattern as the product of a CPG requi res evidence that its generation, patterning, and coordination are independ ent of sensory input. To provide such evidence, we used optoelectronic inst rumentation to obtain high-resolution records of the movement trajectories of individual whiskers in rats whose heads were fixed to isolate their expl oratory whisking from exafferent inputs. Unconditioned whisking patterns we re quantitatively characterized by a biometric analysis of the kinematics, rhythmicity, and coordination of bilaterally homologous vibrissa movements. Unilateral and bilateral sectioning of the infraorbital nerve, which inner vates the whiskers, was then performed to block reafferent inputs generated by the animal's own whisking movements. Unilateral sectioning of the nerve has no effect on whisking kinematics but is followed by a significant but relatively transient bilateral increase in whisking frequency. However, bil ateral deafferentation, when performed in a single-stage procedure, does no t disrupt the generation, patterning, or bilateral coordination of whisking patterns in the rat. These findings provide strong behavioral evidence for a whisking CPG and are discussed in relation to its possible location and properties.