Abstract
Whisking mediated touch is an active sense whereby whisker movements are modulated by sensory input and behavioral context. Here we studied the effects of touching an object on whisking in head-fixed rats. Simultaneous movements of whiskers C1, C2, and D1 were tracked bilaterally and their movements compared. During free-air whisking, whisker protractions were typically characterized by a single acceleration-deceleration event, whisking amplitude and velocity were correlated, and whisk duration correlated with neither amplitude nor velocity. Upon contact with an object, a second acceleration-deceleration event occurred in about 25% of whisk cycles, involving both contacting (C2) and non-contacting (C1, D1) whiskers ipsilateral to the object. In these cases, the rostral whisker (C2) remained in contact with the object throughout the double-peak phase, which effectively prolonged the duration of C2 contact. These “touch-induced pumps” (TIPs) were detected, on average, 17.9 ms after contact. On a slower time scale, starting at the cycle following first touch, contralateral amplitude increased while ipsilateral amplitude decreased. Our results demonstrate that sensory-induced motor modulations occur at various timescales, and directly affect object palpation.
Highlights
Rats explore their proximal environment through periodic and non-periodic protractions of their mystacial vibrissae
We considered the largest amplitude in a whisk cycle to be the onset of retraction, and so in cases where the second peak after touch was lower than the first one, this cycle was not considered as having a Touch Induced Pumps (TIPs)
We found that actively touching an object caused changes in whisking patterns on both the ipsilateral and contralateral sides, at two different timescales
Summary
Rats explore their proximal environment through periodic and non-periodic protractions of their mystacial vibrissae (whiskers). When a stationary rat whisks unobstructed, its whisker movements are generally highly periodic and bilaterally symmetric [11,12]. Periodicity in the motor output persists during sensory nerve inactivation [13], as well as following cortical ablation [13,14]. This suggests that a default periodic state of whisking is generated by a sub-cortical central pattern generator (CPG), rather than resulting from cycle-to-cycle feedback control. Periodicity and symmetry often break down during head movements [15] or contact [16,17], which suggests that both efferent and afferent signals can induce deviations from periodic whisking
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