The Communicative Functions of Touch in Humans, Nonhuman Primates, and Rats: A Review and Synthesis of the Empirical Research

A meta-analysis examined emotion recognition within and across cultures. Emotions were universally recognized at better-than-chance levels. Accuracy was higher when emotions were both expressed and recognized by members of the same national, ethnic, or regional group, suggesting an in-group advantage. This advantage was smaller for cultural groups with greater exposure to one another, measured in terms of living in the same nation, physical proximity, and telephone communication. Majority group members were poorer at judging minority group members than the reverse. Cross-cultural accuracy was lower in studies that used a balanced research design, and higher in studies that used imitation rather than posed or spontaneous emotional expressions. Attributes of study design appeared not to moderate the size of the in-group advantage.

The mothers of infant rats show individual differences in the frequency of licking/grooming and arched-back nursing (LG-ABN) of pups that contribute to the development of individual differences in behavioral responses to stress. As adults, the offspring of mothers that exhibited high levels of LG-ABN showed substantially reduced behavioral fearfulness in response to novelty compared with the offspring of low LG-ABN mothers. In addition, the adult offspring of the high LG-ABN mothers showed significantly (i) increased central benzodiazepine receptor density in the central, lateral, and basolateral nuclei of the amygdala as well as in the locus ceruleus, (ii) increased alpha2 adrenoreceptor density in the locus ceruleus, and (iii) decreased corticotropin-releasing hormone (CRH) receptor density in the locus ceruleus. The expression of fear and anxiety is regulated by a neural circuitry that includes the activation of ascending noradrenergic projections from the locus ceruleus to the forebrain structures. Considering the importance of the amygdala, notably the anxiogenic influence of CRH projections from the amygdala to the locus ceruleus, as well as the anxiolytic actions of benzodiazepines, for the expression of behavioral responses to stress, these findings suggest that maternal care during infancy serves to "program" behavioral responses to stress in the offspring by altering the development of the neural systems that mediate fearfulness.