Why might rats exposed to more licking and grooming from their mothers show less fear and stress than rats not exposed to this grooming behavior?

Habituation to stress and response management

Explanation:

The grooming behavior in this case is acting like an external alteration mechanism. When rats are exposed to this mechanism, they became habitual to the other environmental stresses as the grooming always prevents a negative response. On the other hand, those rats who aren't exposed to this behavior show more fear because they take up stress easily and this promotes negative response over and over.