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Generation, coordination, and re-afferent signaling of rhythmic whisking in rodents


Exploratory "whisking" is a rhythmic motor activity that enables rodents to locate objects in their environment through physical contact with their mystacial vibrissae. How the nervous system generates this rhythmic movement, and how the resulting movement enables these animals to determine the position of objects remain unknown. There are ethological similarities between whisking and sniffing, which may suggest that these two exploratory activities have related underlying neural control circuits. We discuss the similar dynamics of these two active sensory behaviors, and how they shape their respective sensory inputs. We demonstrate that the motor patterns for these behaviors are coordinated by respiratory centers in the ventral medulla. Specifically, we identify a region in the ventral medulla that provides rhythmic input to the facial motoneurons to drive coordinated vibrissa protraction, and we show that this region is under direct control of the respiratory patterning circuitry. Because vibrissa-based object localization may require sensory signals of this self-generated movement, we consider the representation of whisking in the brainstem trigeminal sensory nuclei and their respective target thalamic nuclei. Specifically, there are two major parallel anatomical pathways from these nuclei to primary somatosensory cortex. We demonstrate that a single pathway simultaneously conveys sensory signals of whisking and touch. Neurons in this pathway are diversely tuned to these two sources of sensory input

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