The development of whisker control in rats in relation to locomotion.

Adult rats sweep their large facial whiskers (macrovibrissae) back and forth in a rhythmic pattern known as "whisking". Here we examine how these whisker movements develop in relation to other aspects of exploratory behavior, particularly locomotion. We analyzed 963 high-speed video recordings of neonatal rats, from P1 (Post-natal day 1) to P21, and measured the emergence of whisker control and of head, body, and limb movements. Prior to P11, whisker movements were largely limited to unilateral retractions accompanying head turns. Between P11 and P13 bilateral whisking emerged alongside increased forward locomotion and improved control of the head. Contact-induced modulations of whisking symmetry, synchrony, and whisker spread emerge shortly thereafter but continue to develop until at least P18, coinciding with the emergence of adult-like locomotion patterns such as rearing. Overall, whisking develops alongside increasing locomotor competence indicating that active vibrissal sensing plays an important role in the exploratory behavior of the developing animal.