Social facial touch in rats.

We know much about how rats use their whiskers to discriminate simple tactile properties, but little about how they are used in natural settings. Here we studied whisker motion during social interactions between rats in order to gain a better understanding of natural whisker use in this model system for sensorimotor integration. In the first set of experiments, an intruder was placed in a second rat's home cage. Anogenital sniffing immediately ensued; later in the trial, facial interactions occurred at least as frequently. Whereas much previous work has focused on the importance of anogenital sniffing during social interactions, these facial interactions were accompanied by some of the most intense whisker behaviors described to date. Whisker trimming increased biting but reduced boxing. In addition, whiskers were more protracted and whisking amplitude was larger in aggressive than in nonaggressive interactions. In a second set of experiments, rats interacted facially across a gap. As rats approached each other, whisking amplitude decreased and whiskers were more protracted. Whisker trimming disrupted facial alignment and reduced the frequency of interactions, indicating that whisker use, and possibly whisker protraction, is important for rats to orient themselves with respect to one another. We also found that females whisked with smaller amplitude when interacting with males than with females, and that they held their whiskers less protracted than males. The natural whisker use described here should further our understanding of this important somatosensory system during social interactions.